A GUIDE FOR REDUCING
AUTOMOTIVE AIR POLLUTION
Prepared for the
OFFICE OF AIR PROGRAMS
ENVIRONMENTAL PROTECTION AGENCY
November 1971
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A GUIDE FOR REDUCING AUTOMOTIVE AIR POLLUTION
Prepared for the
OFFICE OF AIR PROGRAMS
THE ENVIRONMENTAL PROTECTION AGENCY
November 1971
By
ALAN M. VOORHEES & ASSOCIATES, INC.
Westgate Research Park
McLean, Virginia 22101
and
RYCKMAN, EDGERLEY, TOMLINSON & ASSOCIATES
12161 Lackland Road
St. Louis, Missouri 63141
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ACKNOWLEDGMENTS
This report was prepared pursuant to contract No. CPA 70-100 by
Alan M. Voorhees & Associates, Inc., and Ryckman, Edgerley, Tomlinson
& Associates, Inc., under the guidance of the staff of the Office of Air
Programs, Environmental Protection Agency. The text contained herein
is substantially that of the contractors.
The project team at Alan M. Voorhees & Associates, Inc. (AMV)
and Ryckman, Edgerley, Tomlinson & Associates, Inc. (RETA) consisted
of:
AMV RETA
Mr. Alan M. Voorhees Dr. Edward Edgerley, Jr.
Project Director Project Manager
Dr. SalvatoreJ. Bellomo Dr. Frederick Brunner
Project Manager & Coordinator Environmental Engineer
Mr. Robert L. Morris
Vice President
Mr. Edward Mierzejewski
Transportation Engineer
Mr. David McBrayer
Transportation Planner
Miss Sally D. Liff
Transportation Planner
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CONTENTS
Chapter
PREFACE vii
MANDATES FOR COPING WITH AIR POLLUTION . 1-1
The Need for Traffic Controls 1-1
Federal Legislation 1-1
A. National Environmental Policy Act of 1969 . . 1-1
B. 1970 Clean Air Act 1-2
C. Regulations Promulgated Pursuant to
Clean Air Act 1-3
D. 1970 Federal-Aid Highway Act 1-4
E. Urban Mass Transportation Assistance Act
of 1970 1-4
State Legislation 1-5
SUMMARY AND CONCLUSIONS 2-1
AIR POLLUTION REDUCTION THROUGH TRAFFIC
CONTROL 3-1
Basic Relationships 3-1
Techniques for Improving Traffic Flow 3-6
A. Freeways 3-6
1. Reverse Lane Operations 3-6
2. Driver Advisory Displays 3-7
3. Ramp Control 3-8
4. Interchange Design 3-9
B. Arterials 3-9
1. Alinement 3-9
2. Widening Intersections . 3-10
3. Parking Restrictions 3-12
4. Signal Progression 3-13
5, Reversible Lanes 3-14
6. Reversible One-Way Streets 3-14
7. Helicopter Reports 3-15
8. Miscellaneous 3-15
C. Downtown Distribution 3-15
1. Traffic Responsive Control 3-16
2. One-Way Street Operations 3-16
3. Loading Regulations. 3-17
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CONTENTS (Continued)
Chapter
4. Pedestrian Control 3-18
5. Traffic Operations Program to Increase .
Capacity and Safety (TOPICS) 3-18
Techniques for Reducing Pollution Concentration. . . 3-20
A. Staggered Work Hours 3-20
B. Roadway Concentration 3-22
C. Cross-Sections 3-22
D. Elevated, At-Grade, Depressed Roadways . . 3-26
Techniques for Reducing Auto Traffic 3-26
A. Transit Operations 3-27
1. Bus Lanes on City Streets 3-27
2. Bus Lanes on Freeways 3-27
3. One-Way Streets with Two-Way Buses . . 3-28
4. Park-Ride, Kiss-Ride 3-28
5. Service Improvements and Cost
Reductions 3-29
B. Regulation 3-30
1. Parking Bans 3-31
2. Auto-Free Zones 3-31
3. Gasoline Rationing 3-32
4. Idling Restrictions 3-32
5. Four-Day, Forty-Hour Week 3-32
C. Pricing Policy 3-33
1. Parking Policy . 3-36
2. Road User Tax 3-37
3. Gasoline Tax 3-37
4. Car Pool Incentives 3-38
D. Planned Unit Development 3-38
Appendix
A INTRODUCTION TO AIR POLLUTION A-l
Types of Pollutants and Their Sources . . A-l
A. Classification of Pollutants .. ........ A-l
B. Units of Air Pollution Measurement , .... . . . A-2
C. Classification of Sources .. , . A-3
Variations in Air Pollution Concentrations ...... A-3
A. Variations According to Location , A-4
B. Variations by Time Periods . A-5
II
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CONTENTS
Appendix
Meteorology ...................... A-8
Site Conditions Affecting Dispersion ......... A-10
A. Urban Heat Island Effect ....... • • • • A~10
B. Building Configuration ............. A-12
C. Roughness Effects . . . ............ A -13
GLOSSARY ....... ............... B-l
REFERENCES. ...... ......... ..... C-l
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TABLES
Table
2. 1 Techniques for Improving Traffic Flow, For
Reducing Pollution Concentration, and For Reducing
Auto Traffic 2-3
3.1 Typical Levels of Concentration of Pollutants in
Exhaust Gases 3-1
3. 2 Emission Factors For Gasoline Powered Motor
Vehicles 3-3
3.3 Emissions Versus Load Factor 3-12
3.4 Benefits of Traffic Management Scheme, Gateshead. . 3-19
A-l Estimated Emissions of Air Pollutants By Weight,
Nationwide, 1969 A-4
IV
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FIGURES
Figure Page
3. 1 Relative Emission of Carbon Monoxide During
Operating Cycle Between Stops 3-2
3. 2 Speed Adjustment Factors for Carbon Monoxide
and Hydrocarbons 3-4
3. 3 Typical Speed/Volume Curve Under Ideal Uninter-
rupted Flow Conditions on Freeways and Express
ways , 3-6
3. 4 Urban Intersection Approach Service Volume for
Two-Way Streets With No Parking 3-11
3. 5 Urban Intersection Approach Service Volume for
Two-Way Streets With Parking 3-11
3. 6 Typical Relationships Between Volume/Capacity Ratio
and Average Overall Travel Speed, . . Direction
of Travel on Urban and Suburban Arterial Streets . . 3-14
3. 7 Effects of Staggered Work Hours Hudson Terminal
Afternoon Passenger Volumes 3-21
3. 8 Carbon Monoxide Concentrations Depending Upon
Traffic Volumes 3-23
3. 9 Pollution Level Versus Distance to Edge of
Roadway , 3-24
3.10 Pollution Level Versus Height Above Roadway. . . . 3-24
3.11 Carbon Monoxide Concentrations for a Highway
Design 3-25
3.12 Supply-Demand Relationships 3-34
3.13 Effects of Parking Costs on Vehicular Air Pollution
Emissions 3-36
A. 1 Hourly Carbon Monoxide Concentrations on Weekdays
in Detroit Area A-5
A. 2 Hourly Carbon Monoxide Concentrations on Weekdays
in New York Area A-6.
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FKiUKES (Continued)
Figure Page
A. 3 Hourly Carbon Monoxide Concentrations on Weekdays
in Los Angeles Area A-6
A. 4 Concentrations of Nitric Oxide, Nitrogen Dioxide,
Hydrocarbon, and Oxidant During a Smoggy Day in
Cincinnati, Ohio A-7
A. 5 Urban Circulation and Dispersion After Sunrise .... A-ll
A. 6 Urban Circulation and Dispersion After Sunset A-12
VI
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PREFACE
This Guide is designed to aid transportation professionals and
state air pollution control agencies in selecting transportation controls
suggested in the regulations promulgated pursuant to the Clean Air Act
of 1970 . Actions considered here emphasize the reduction of traffic
volume and congestion, and can be implemented within five years. The
impact of the suggested actions is not fully understood. Research is now
underway on many aspects of the relationship of auto traffic to air pollution.
As results become known, the list of suggested actions almost certainly
will need revision.
Three other studies that will expand understanding in this area are
funded by the Environmental Protection Agency (EPA) and will complement
this Guide. One study discusses the legal, institutional, and administrative
problems of implementing traffic controls in selected cities. Another
covers the longer range air quality implications of transportation and land
use planning strategies. In addition, EPA is preparing information on the
effectiveness of motor vehicle inspection programs and of emission control
devices for in-use vehicles.
The Guide outlines the laws and regulations that require assessment
of the air pollution impact of transportation. It then discusses techniques
for improving traffic flow, for reducing the concentration of pollution and
for reducing auto traffic. The appendixes provide basic information on
air pollution.
Ronald A. Venez ia
Chief, Office of Land Use Planning
Office of Air Programs
Environmental Protection Agency
vn
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CHAPTER 1
MANDATES FOR COPING WITH AIR POLLUTION
THE NEED FOR TRAFFIC CONTROLS
Increasing public opinion and legislation indicate that serious efforts
to reduce the amount of air pollution caused by transportation are necessary.
Although such reduction will be highly dependent on controlling emissions
at their source, urban planning, transportation planning, and traffic
engineering can significantly improve air quality. Such measures should
complement a source control strategy for most effective emission reduction.
Measures that can be used include the improvement of traffic flow,
the dispersal of motor vehicle traffic in time and space, the reduction of the
overall amount of vehicular travel, and greater use of vehicles with low
emission characteristics. The implementation of these measures requires
coordination at all levels of government. Most of the traffic engineering
measures suggested in this Guide would be under the control of a traffic
engineer, who should work with appropriate air pollution control agencies.
Transportation planning measures typically involve city, county, and
regional agencies as well as state and Federal authorities.
FEDERAL LEGISLATION
A. National Environmental Policy Act of 1969
This act establishes a broad national policy directed toward improving
the relationship between man and his environment, and creates the Council
on Environmental Quality (CEQ). Section 102(2)(C) of the act is designed to
ensure that the environmental effects of all major proposed Federal legislation,
plans, and programs are properly considered. For any proposed action
significantly affecting the environment, a detailed statement must be submitted
analyzing the following points:
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"(i) the environmental impact of the proposed action,
(ii) any adverse environmental effects which cannot be
avoided should the proposal be implemented,
(iii) alternatives to the proposed action,
(iv) the relationship between local short-term uses of man's
environment and the maintenance of long-term
productivity, and
(v) any irreversible and irretrievable commitments of
resources which would be involved in the proposed
action should it be implemented. "
2
The Office of Management and Budget has established a framework
for communicating environmental information among Federal, state, and
local agencies. This framework, originally intended to implement require-
ments for coordination set forth in other Federal legislation, was amended
February 9, 1971, to include the coordination of environmental impact
analyses. In this framework, selected state, regional, and local planning
agencies are designated as "clearinghouses" to be notified by any state or
local agency intending to submit an application for Federal financial
assistance. The clearinghouse, in turn, notifies all potentially interested
persons and groups within its jurisdiction of the planned project. The
state or local agency requesting Federal aid may then obtain comments
from these persons and groups on the environmental impact of its project;
and these comments are included in the request to the Federal agency. If,
after reviewing the comments, the Federal agency determines there will be
a significant impact on the environment, it must submit an impact statement
to CEQ. The impact statement, reflecting all the comments received
through the clearinghouse process, becomes part of the public record.
B. 1970 Clean Air Act
This act calls for the establishment of primary (relating to health) and
secondary (relating to welfare) ambient air quality standards by the Admini-
strator of the EPA. The Administrator is also required to set standards of
1-2
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performance for new stationary sources of pollution and for motor vehicles.
The act requires states to prepare plans by January 30, 1972 for achieving
and maintaining the air quality standards within 3 years. The act authorizes
the Administrator to act if the states do not, and gives him powers of
enforcement.
The Senate Committee on Public Works, in hearings on the National
Air Quality Standards Act of 1970 (subsequently replaced by the Clean Air
3
Act Amendments of 1970) reported:
'Transportation policies must be developed or improved
to assure that the impact of pollution from existing moving
sources is reduced to the minimum compatible with the needs
of each region. Construction of urban highways and freeways
may be required to take second place to rapid and mass transit
and other public transportation systems. Central city use of
motor vehicles may have to be restricted. "
C. Regulations Promulgated Pursuant to Clean Air Act
The EPA set out requirements by which the states should prepare,
adopt, and submit implementation plans for air quality standard achievement.
The requirements define a "control strategy" by which a combination of
measures are designated to achieve the aggregate reduction of emission
necessary to achieve and maintain a national standard. The measures
might include:
1. Emission limitations.
2. Federal or state emission charges or taxes, or other
economic incentives or disincentives.
3. Closing or relocation of residential, commercial, or
industrial facilities.
4. Changes in schedules or methods of operating commercial
or industrial facilities or transportation systems. These
would include any short-term changes made in accordance
- with standby plans.
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5. Periodic inspection and testing of motor vehicle emission
control systems.
6. Emission control measures applicable to in-use motor vehicles,
including mandatory maintenance, installation of control
devices, and conversion to gaseous fuels.
7. Measures to reduce motor vehicle traffic, such as
commuter taxes, fuel rationing, parking restrictions or
staggered working hours.
8. Expanded use of mass transportation through measures
such as increased frequency, convenience, or capacity,
or by providing special bus lanes on streets and highways.
9. Any other land use or transportation control measures.
10. Any other variation of, or alternative to, the above measures.
D. 1970 Federal-Aid Highway Act
This act requires the Secretary of the Department of Transportation
(DOT) to promulgate guidelines by October, 1972 designed to ensure that
new highways will be consistent with a state's air quality implementation
plan. These guidelines will enable planners to predict and to minimize the
air quality impact of a proposed roadway. Highways should be designed,
located, and operated so as not to hinder the achievement of air quality
standards. The act also allows highway trust funds to be used for construction
of preferential bus lanes, bus passenger loading areas, and fringe transporta-
tion corridor parking facilities. Detailed information on the act is available
from the state representative of the Federal Highway Administration.
E. Urban Mass Transportation Assistance Act of 1970
This act amends the Urban Mass Transportation Act of 1964, placing
2
grant and loan applications under the "A-95" review process. In addition
1-4
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it requires that the applicant afford adequate opportunity for public hearings
for all parties interested in the economic, social, and environmental impact;
and must hold the hearings unless no one with significant economic, social,
and environmental interest has requested such hearings. If hearings are
/
held, the Secretary of DOT is required to ascertain that they were adequate
and that all harmful environmental impacts have been minimized. Detailed
information on the act is available from the Administrator, Urban Mass
Transportation Administration, Washington, D. C., 20590.
STATE LEGISLATION
Most state laws that relate to the measures described in this Guide
concern inspection systems and the reduction of emissions from individual
motor vehicles. Arizona, California, Colorado, Delaware, Florida, Kansas,
Louisiana, New Jersey, New Mexico, New York, North Carolina, Texas,
and Vermont require annual inspection and approval of motor vehicle emission
control systems. Nine additional states have the legal authority necessary to
conduct inspections. Twenty-two states require that control equipment
required by Federal law be maintained and not removed, but only half of
these are among those states which actually inspect annually.
New Jersey is now preparing to require all cars registered in the state
to be tested annually for carbon monoxide and hydrocarbon emissions. Cars
violating the standards will be barred from the roads after 2 weeks of grace
in which to make required repairs. New Jersey's Department of Environ-
mental Protection estimates that in the first year of operation, the inspection
system will reduce carbon monoxide emissions by 20 percent and hydrocarbon
emissions by 32 percent.
When inspection systems are included as part of a state's implementation
plan, EPA will review the pollution-reduction effectiveness of such systems.
1-5
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CHAPTER 2
SUMMARY AND CONCLUSIONS
The major points to be summarized from this Guide are:
1. Air pollution caused by automotive emissions is a serious
problem.
2. Corrective action must be taken.
3. Much improvement can be achieved through traffic
operation and transportation planning measures.
These measures, which supplement the efforts of government and
industry to reduce automotive emissions at the source, encompass the
following means of reducing harmful exposure to air pollutants:
1. Smoothing the flow of traffic.
2. Reducing concentrations of traffic, both geographically
and by time of day.
3. Reducing the total amount of travel.
The Guide lists and discusses a number of techniques. All have been
previously used, or at least proposed in the context of improving the capacity
and quality of urban transportation systems. Not all of the techniques will
apply to every city, but some should. Their aggregate impact will increase
the likelihood of improving air quality standards.
Table 2.1 lists the techniques with which this Guide is concerned.
While it is impossible to place a precise measure of effectiveness on each
technique, there is sufficient knowledge to assign an approximate value.
This, shown on the table as "Probable Effectiveness, " uses a scale of 1
(least effective) through 5 (most effective). The effectiveness of most
techniques in reducing air pollution varies from one city to another for
such reasons as the extent to which the technique is already in use, the
adequacy of the area's transportation system, or the micro-climate of the
area. The difficulty of implementing specific techniques depends on such
factors as:
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1. The existence of necessary legislation.
2. The willingness of state legislatures to pass new
legislation.
3. The ability of the appropriate government agencies to
administer transportation controls within the existing
institutional framework.
4. The existence of alternative transportation modes.
5. The costs of implementation.
6. The strong support of the public.
Although some measures must be applied on a state or even national
scale, some techniques may be most appropriately applied during severe
pollution episodes.
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TABLE 2. 1
TECHNIQUES FOR IMPROVING TRAFFIC FLOW, FOR REDUCING
POLLUTION CONCENTRATION, AND FOR REDUCING AUTO TRAFFIC
Techniques for Improving Traffic Flow
A. Freeways
1. Re verse-lane operations 3
2. Driver advisory displays 1
3. Ramp control 2
.4. Interchange design 2
B. Arterials
1. Alinement 1
2. Widening intersections 3
3. Parking restrictions 2
4. Signal progression 2
5. Reversible lanes 3
6. Reversible one-way streets 3
7. Helicopter reports 2
C. Downtown Distribution
1. Traffic responsive control 5
2. One-way street operations 3
3. Loading regulations 3
4. Pedestrian control 1
5. Traffic Operations Program to Increase
Capacity and Safety (TOPICS) 5
Techniques for Reducing Pollution Concentration
A. Staggered Work Hours 3
B. Roadway Concentrations 2
C. Cross-sections 2
D. Elevated, At-grade, Depressed Roadways 2
Techniques for Reducing Auto Traffic
A. Trans it Operat ions
1. Bus lanes on city streets 1
2. Bus lanes on freeways ' 1
3. One-way streets with two-way buses 1
4. Park-ride, kiss-ride 3
5. Service improvements and cost reductions 2
B. Regulation
1. Parking bans 4
2. Auto-free zones 4
3. Gasoline rationing 5
4. Idling restrictions 2
5. Four-day, forty-hour week 2
C. Pricing Policy
1. Parking policy 2
2. Road-user tax 5
3. Gasoline tax 5
4. Car pool incentives 2
D. Planned Unit Development 2
Based on traffic volume affected, pollution reduction, population exposure, and any adverse
pollution impact (e. g., more or lorger trips likely to be induced, or likely to cause traffic
congestion). Higher numbers indicate greater levels of effectiveness.
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CHAPTER 3
AIR POLLUTION REDUCTION THROUGH TRAFFIC CONTROL
An understanding of the basic relationships between air pollution
and transportation operating variables will indicate how traffic control can
be used to reduce pollutants. In this chapter, these relationships are set
forth, the implications are evaluated, and techniques are suggested for
the effective control of traffic.
BASIC RELATIONSHIPS
In simplified terms, the emission of the principal pollutants related
to urban vehicles -- carbon monoxide and hydrocarbons -- increases as
average speed decreases, and decreases as average speed increases. There
is some evidence that the reverse is true for oxides of nitrogen (i. e., that
NO emissions increase slightly as traffic speeds increase), but this rela-
ji
tionship has not yet been satisfactorily quantified. Table 3. 1, based on a
4
1967 British report, indicates a relationship between vehicle operation and
the level of pollutant emissions. These emissions are from uncontrolled
autos; it should be expected that today's emission rates from controlled
vehicles are lower.
Table 3. 1. TYPICAL LEVELS OF CONCENTRATION
OF POLLUTANTS IN EXHAUST GASES
Pollutant
Carbon monoxide,
% by volume
Hydrocarbons, ppm
Oxides of nitrogen, ppm
Idling
7.0
820
30
Accelerating
3.0
700
1,050
Cruising
4.0
500
650
Decelerating
3.0
4,400
20
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The same report considered the relative rates at which successive
sections of a length of roadway are polluted by carbon monoxide. The case
chosen for study was that of three cars stopping at traffic signals, idling,
accelerating to 30 mph, running at that speed, decelerating for a stop at a
traffic light 800 feet away, and repeating the cycle. The result is illustrated
in Figure 3. 1 which shows the highly localized peak just before the traffic
lights due to idling levels of carbon monoxide from stationary vehicles. The
o
o
u.
O
UJ
UJ
UJ
oc
6-1
5-
4-
3-
2-
1-
TRAFFIC LIGHTS
100
200
300
400 500
600
700 800
DISTANCE, feet
Figure 3.1. Relative emission of carbon monoxide during
operating cycle between stops.4
subsequent acceleration of the vehicles results in an immediate reduction in
local carbon monoxide pollution because, although the rate at which exhaust
gas is emitted is higher than when the engine is idling, the time the vehicle
spends in each successive unit of roadway diminishes as the vehicle gathers
3-2
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speed. When the car attains a uniform speed of 30 mph, there is a reduction
in power requirement and pollution; a further reduction in carbon monoxide
emission occurs when the vehicle begins to decelerate because the throttle
is still further closed.
The relative emissions of carbon monoxide while idling are more than
six times the cruising rate; however, exhaust concentrations of carbon
monoxide while idling are less than twice concentration while cruising.
This is merely a reflection of the fact that when idling, a much longer time
period is spent per unit of roadway.
CL £J
Another study ' indicates a direct correlation between increased
average vehicle speeds and decreased emissions of carbon monoxide and
hydrocarbons. See Table 3. 2 and Figure 3.2.
Table 3.2. EMISSION FACTORS*1 FOR GASOLINE
POWERED MOTOR VEHICLES
Emissions
Carbon Monoxide
Hydrocarbons
Evaporation
Crankcase
Exhausts
Nitrogen Oxides
(N02)
1960
120
2.7
4. 1
16
8
1965
120
2.7
2.:7
16
8.5
1970
95
2.7
0.9
12
9
1972
85
2.3
0.45
9.5
9
1974
75
1.8
0.22
7.2
7.5
1975
60
1.4
0.22
6
7
cL
Grams per vehicle mile at 25 mph.
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10
35
Figure 3.2. Speed adjustment factors for carbon monoxide
and hydrocarbons.5'6
The emission and speed adjustment factors of Figure 3. 2 are for
passenger cars, light-duty trucks, and gasoline-powered heavy-duty
vehicles, in proportion to their use. Allowance is made for deterioration
and scrapping of vehicles as they age, and their replacement by new
vehicles. The emission factors of Table 3. 2 are for urban driving
conditions with an average speed of 25 mph, beginning from a cold start.
To determine carbon monoxide and hydrocarbon emission factors for
average speeds other than 25 mph, use Figure 3. 2. For example, Table 3. 2
shows that the emission factor for hydrocarbon exhaust emissions in 1970
was 12 (at 25 mph). To determine the same factor at an average speed of
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10 mph, refer to Figure 3.2, which shows a hydrocarbon adjustment factor
of 1. 79 (approximately) for that speed. Multiplying the emission factor of
12 by the 1. 79 adjustment factor gives 21.4 as the emission factor at 10 mph.
CAUTION
The reader is cautioned that Figure 3. 2 is based on
average speed, not on constant or cruise speed where
acceleration and deceleration are not involved.
Increasing cruise speed much above 30 mph may
increase carbon monoxide and hydrocarbon emissions
per vehicle mile. Thus, the traffic engineering
recommendations contained in this Guide should not
be construed as recommendations for additional
urban freeways.
If the objective is to minimize the concentration of carbon monoxide
and hydrocarbons, any measure would be beneficial which would smooth
the flow of traffic by reducing rapid acceleration and deceleration of
vehicles. Some techniques for accomplishing this are described below.
The reader should clearly understand, however, that easing congestion
may have ancillary effects that would tend to under mime the goal of cleaner
air. The relationship between increased travel speed and increased trip
7
length has been well established. Furthermore, a reduction in congestion
may tend to induce more people to drive. If steps are not taken to reduce
auto travel, the net result of improved traffic flow might be more, longer,
and more dispersed trips with greater amounts of pollutants spread over
a wider area. Thus, it is strongly recommended that other measures set
forth below be used concomitantly with improved traffic flow techniques
to reduce the overall number and length of automobile trips in urban areas.
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TECHNIQUES FOR IMPROVING TRAFFIC FLOW
A. Freeways
Freeways have been the subject of numerous operational studies and
experiments. As a result, the techniques for improving traffic flow on
freeways are relatively well developed.
1. Reverse Lane Operations -- Under this type of operation, one or
more lanes are designated for movement in one direction during part of the
day and in the opposite direction during another part of the day.
Current examples of the use of this technique include Arlington
(Virginia), Detroit, Cleveland, Los Angeles, Boston, and Chicago. To
illustrate the effect of reverse-lane operations, assume that Figure 3. 3
represents the relationship between average speed and volume per lane for
a freeway operating under ideal conditions.
D
ui
HI
0.
V)
111
(D
<
CC
01
70
60
50
40
30
20
STABLE FLOW
-««*•- FORCED FLOW
A THREE LANES PEAK FLOW
I ONE LANE MINOR FLOW)
I I I
B TWO LANES EACH WAY
I I 1 I
c WITHOUT DRIVER ADVISORY DISPLAYS
I I I I I I I I I 1
D WITH DRIVER ADVISORY DISPLAYS
MINIMUM
£
UJ
>
§
5 10 15
AVERAGE LANE VOLUME, 100 passenger cars/hr.
20
MAXIMUM
Figure 3.3. Typical speed/volume curve under idea I uninterrupted
flow conditions on freeways and expressways.8
3-6
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In Figure 3. 3 speed is not a function of volume; speed and volume are
both functions of vehicle density. Movement along the curve from the upper-
left to the lower left represents constantly increasing vehicle density on
the freeway. The upper portion of the curve shows the relationship between
volume and speed up to a critical vehicle density. Beyond this point, a
further increase in density causes the speed to decrease rapidly, with a
simultaneous decrease in the average lane volume or rate of flow.
Assuming that in one direction there is a demand for 5, 000 trips per
hour during the peak period on a four-lane (two lanes each way) freeway,
the capacity of the facility will be exceeded and it may well be operating
at point B -- 10 miles per hour with extremely forced flow and long queues
of vehicles. If, however, it is feasible to allow the facility to operate with
three lanes in the peak direction and one lane in the minor flow direction,
operation could be at point A -- 1, 667 vehicles per hour per lane, 45 miles
per hour, with relatively smooth flow.
This increased average speed in the major direction of flow could
mean substantial reductions in carbon monoxide and hydrocarbon emissions
during the peak period, even if free flow was no longer achieved in the
reverse direction.
2. Driver Advisory Displays' -- When an expressway is closely paralleled
by one or more arterial streets which serve as alternative routes, the use
of driver advisory displays can improve the level of traffic flow. The
objective is relatively simple -- to advise motorists of the traffic conditions
on a freeway, thereby encouraging the use of alternative routes when the
freeway is congested. The technique has been used in conjunction with ramp
control measures on Chicago's Eisenhower Expressway.
To be operational, driver advisory displays must be placed well in
advance of the arterial which serves as an alternative to the expressway.
Each sign shows traffic conditions by means of color-coded arrows which
are automatically controlled from continuous expressway and ramp traffic
measurements.
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It is difficult to predict the consequences of driver advisory displays
since their only use to date has been in conjunction with ramp metering.
It is reasonable to assume that motorists will not be diverted from the
freeway unless it is congested. Even though driver advisory displays
probably will not divert sufficient traffic to permit the average peak-hour
speed to approach the design speed of the freeway, the displays could
mean the difference between operating at point C or point D in Figure 3. 3.
Although both points represent the same lane volume, D is in the stable
part of the curve at 42 miles per hour, while C is in the forced flow region
at 26 miles per hour. Emissions of carbon monoxide and hydrocarbons
would therefore be significantly reduced at point D.
For such an approach to improve the ambient air quality, the arterial
alternative to the freeway must have sufficient excess capacity to carry
diverted traffic at a high level of service; i.e., with little congestion.
3. Ramp Control -- To improve the operating conditions on congested
freeways, ramp control (frequently called ramp metering) is a technique
that is increasing in usage. Ramp control measures are presently utilized
in several locations, including Chicago's Eisenhower Expressway, the
John Lodge Freeway in Detroit, the Gulf Freeway in Houston, and the
Harbor Freeway in Los Angeles. The technique consists of monitoring
freeway traffic volumes and, by some form of traffic control (e. g., a signal)
regulating the number of vehicles that can enter the freeway via its ramp
system. When freeway volumes approach practical capacity, the number
of vehicles permitted to use entry ramps is limited. The technique has
been effective. From the point of view of reducing air pollution, it should
be noted that resultant traffic delays at ramps raise emissions there; but,
for the freeway as a whole, the amount of congestion and resultant pollution
are lowered. One advantage over the previous method described is that
ramp control is enforceable and not merely advisory.
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A study of the Eisenhower Expressway and the adjacent street system
failed to disclose any deterioration of surface street traffic operations
attributable to the ramp controls except at the entrance-ramp/arterial-street
terminals where queues interfered with traffic movements.
Apparently the variety of trip origins and destinations permitted
several alternative routes to absorb diverted traffic. In addition, it is
suspected that many diverted expressway trips are short in length, thereby
allowing the freeway to perform at a higher level for longer trips.
Similar findings were reported for the Harbor Freeway in Los Angeles,
where the effect of the added load on streets was too small to measure.
4. Interchange Design --In most urban areas, the critical determinants
of the level of service on freeways are the characteristics of interchanges
and weaving sections, because the capacity of a freeway lane is much less
when merging or weaving occurs than it is under uninterrupted flow conditions.
Certainly, the air quality impact should be a consideration of the highway
engineer when deciding on the design of new facilities, especially at interchanges.
B. Arterials
Arterials are the backbone of most urban street systems. Although
these systems are commonly obsolete for modern traffic demands, much
can be done to improve their effectiveness.
1. Alinement -- Due to the increased emission rate when vehicles
accelerate or decelerate, the best highway design from an air quality stand-
point is one in which the motorist can travel at a constant speed. Horizontal
alinement should be free from small radius curves, which would necessitate
braking and accelerating again.
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The vertical grade can have a very significant impact on the rate of
emissions. To maintain a constant speed, a vehicle is effectively accelerating
on an upgrade and decelerating on a downgrade. In the interests of air
quality, vertical grades should be as small as possible, consistent with good
drainage and design practice.
2. Widening Intersections — The width of the approach to an intersection
has proved to have the most bearing on its capacity. Figure 3.4 illustrates
the width/capacity relationship for an urban intersection used for two-way
operation with no parking permitted.
Example:
Consider the case of an urban arterial with two 12-foot
lanes in each direction (a 24-foot approach width) at
an intersection with an approach volume of 2, 200 vehicles
per hour of green time. As illustrated in Figure 3. 4,
the approach would be operating at a load factor of 1. 0--
very unstable, inducing considerable vehicle delay.
(Load factor is defined as the number of fully utilized
green intervals divided by the total number of green
intervals for the same period.) If an additional lane
were added in each direction (a 36-foot approach width)
operation could be at a load factor of 0. 0--free flowing,
with almost no intersection delay.
Thus, widening the approaches to intersections, which can be achieved
by minor construction, can greatly improve arterial street operations. The
favorable effect on air pollution is indicated in Table 3.3. Widening of
course is not always possible, particularly in intensively developed urban
areas.
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o
IT
10 20 30 40 'jO
CURB TO DIVISION LINE APPROACH WIDTH li
Figure 3.4. Urban intersection approach service volume for
two-way streets with no parking.8
1
.c
o
I
5?
o
c
I
u 10 20 30 40 50 60
CURB TO DIVISION LINE APPROACH WIDTH, ll
Figure 3.5. Urban intersection approach service volume for
two-way streets with parking-8
3-11
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Table 3. 3. EMISSIONS VERSUS LOAD FACTOR
Load
Factor
0.0
0.1
0.3
0.7
1.0
Overall Travel
Speed, mph
30
25
20
15
10
a
CO Emissions, g
gm/vehicle mile
76.5
85.0
102.0
136.0
178.5
a
HC Emissions, ^
gm/vehicle mile
11.0
12.0
13.5
17.2
22. 1
a 1972 vehicle mix.
3. Parking Restrictions -- Parking conditions at an intersection approach
have a pronounced effect on intersection capacity. Because motorists fear
sudden maneuvers or opening doors of parked cars, the width of roadway
influenced by a parked vehicle is much greater than its physical width.
Figure 3.5 illustrates the approach service volumes for two-way streets
with parking.
When compared with Figure 3.4, for the case with no parking, the
impact of parking on intersection performance is quite apparent.
Example:
Assume that an urban arterial consists of three 10-foot
lanes in each direction (a 30-foot approach width), with
parking in the curbside lane. An approach volume of
2, 000 vehicles per hour of green would overload the
intersection approach, causing it to operate in the
forced-flow region, with a load factor of approximately
1. 0 (see Figure 3. 5). If, as a remedial measure,
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parking is prohibited, a 30-foot approach width can
handle 2, 000 vehicles per hour of green time at a
load factor of 0. 1 -- providing a high level of service
and minimal delays (see Figure 3.4).
In addition to increasing the capacity of intersection approaches,
parking prohibition contributes to smooth traffic flow with less interference
along the route. In many cases local opposition may make parking prohibi-
tions politically unfeasible; e. g., local merchants may oppose discontinua-
tion of parking. A useful compromise is to prohibit parking only during
peak flow periods.
4. Signal Progression -- Signals along an arterial can be coordinated
to provide progressive movement if the timing of one signal relative to
the next is arranged to permit continuous movement of vehicles through
the system.
A progressive operation can best be achieved if:
1. There are relatively few turning movements.
2. The demand per cycle can be held slightly under
the capacity per cycle.
3. Midblock frictional elements are largely absent.
Figure 3. 6 compares typical and progressive arterial operations.
Figure 3. 6 is similar to Figure 3. 3, the speed-volume curve presented in
the section on freeways. Typically, the installation of a progressive
signal system might increase average overall speeds from 20 to 30 miles
per hour with concomitant reductions of carbon monoxide and hydrocarbon
emissions.
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.c
a
Q
LU
HI
a.
in
_i
UJ
-I
<
H
UJ
o
UJ
O
<
oc
UJ
TYPICAL INTERRUPTED FLOW;
UNCOORDINATED SIGNALS
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
VOLUME/CAPACITY RATIO
Figure 3.6. Typical relationships between volume/capacity ratio
and average overall travel speed, in one direction of travel
on urban and suburban arterial streets.8
5. Reversible Lanes -- The reversible-lane concept, previously
mentioned as a freeway technique, applies equally to arterial street
operations. The major advantage of reversible lanes is obvious --
additional capacity is provided in the major flow direction, allowing for
a smoother flow of traffic.
6. Reversible One-Way Streets -- An extension of the reversible lane
concept is to reverse the direction of flow of the entire street, in accordance
with directional peaking characteristics. To warrant reversing the direction
of flow of an entire street, flow in one direction should exceed 80 percent
of the total flow. In addition, adjacent streets must be capable of carrying
the minor flow traffic.
3-14
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7. Helicopter Reports -- Radio traffic report helicopter^ are b
a common sight over many large cities. A helicopter observer relays
current traffic conditions to radio listeners and advises them of the best
routes to take on a particular day. This technique has considerable
potential; i.t is responsive to the day-to-day peculiarities of travel demands
and traffic events. Its success depends on the ability 01 the observer to
advise the motorists properly, as well as the extent to which motorists
listen to the reports.
8. Miscellaneous -- There are numerous other arterial operating
improvements that will both facilitate traffic flow and reduce air pollution.
Improvements such as channelization, lane and other pavement markings,
and traffic signs can greatly upgrade traffic flow and in some measure
reduce emissions.
C. Downtown Distribution
The downtown street system is probably the most complex component of the
urban area road system. From a functional viewpoint, the nature of the
downtown street system is largely circulatory -- designed to service
adjacent land uses -- with the level of service to through traffic of secondary
concern. Traffic flow is interrupted frequently by pedestrian movements,
vehicle turning conflicts, traffic signals, and a high number of stop-start
transit vehicles in the traffic stream. A major portion of vehicle time is
spent idling, accelerating, and decelerating; the result is a relatively high
level of air pollutant emissions. Any operational techniques that can improve
the stop-start nature of downtown traffic flows can significantly reduce air
pollution levels in central cities. Due to the high daytime population
densities, reduction in downtown air pollution levels can benefit a relatively
large percentage of the population.
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1. Traffic Responsive Control -- Considerable attention has been
focused in recent years on computerized traffic control systems. North
American cities with computerized traffic control systems currently in
operation include Toronto, Ontario; San Jose, California; Charleston,
South Carolina; and Wichita Falls, Texas.
Several system designs are available, but certain basic features
are common to all. Traffic flow is measured by a series of sampling
detectors throughout the system network. On the basis of data received
from the sampling detectors, the computer selects, from a number of
programs, the optimal timing for the system.
Control over traffic signal hardware can be either directly from the
computer or through local controllers which are directed by the computer.
Traffic flow information is being received and signal timing revised
continually to meet the varying demands in a near optimal manner.
The Wichita Falls system reduced vehicle stops by 16. 3 percent,
average vehicle delays by 31. 1 percent, and accidents by 8. 5 percent.
Peak-hour average speeds on many downtown approach and exit streets
increased from 20 to over 30 miles per hour. The San Jose system yielded
similar results.
2- One-Way Street Operations -- One-way operation of a given street
is generally more efficient than two-way operation, in terms of total vehicles
per hour. The major advantages of one-way street operation are reduced
turning conflicts at intersections, reduced pedestrian/vehicle conflicts,
and ease of installing a progressive signal system. Major disadvantages of
one-way streets are longer trips for some vehicles, motorist confusion,
less desirable transit service, and the requirement for many additional
traffic control devices.
It is difficult to generalize about the effectiveness of one-way streets
in reducing air pollution. Although they definitely increase average network
speed, this effect is at least partially offset by the overall increase in vehicle
3-16
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miles caused by the necessity for many trips to take a path other than the
shortest. To evaluate the possible effect of a one-way system on air pollution,
a traffic assignment must be prepared to determine if the increase in speed
or the increase in vehicle mileage is the dominating factor. Undoubtedly,
there are many cases in which one-way street systems can effectively
reduce air pollution.
3. Loading Regulations -- In many downtown areas, the loading and
unloading of trucks and other commercial vehicles is a major impediment
to smooth traffic operations. The long-range solution to the conflict between
load ing/unload ing and street traffic is for new buildings to include off-street
loading facilities, as is now required in many cities. However, many
existing buildings must handle their deliveries and shipments from the
street. Even when off-street facilities are used, problems exist in moving
trucks out of (or into) the traffic stream.
An effective measure to alleviate the immediate problem is restricting
loading and unloading time periods. The easiest time restriction to enforce,
and the one of most value to reducing traffic congestion, is to prohibit
loading/unloading during morning and evening peak traffic hours. Since
the largest demand for loading space is from 10:00 a. m. to 4:00 p. m.,
peak hour restrictions are a reasonable measure.
Another measure that can minimize the conflicts between street traffic
and load ing/unload ing vehicles is the use of a street classification system,
designating certain streets (segregated as much as possible from the
arterial street system) as service streets.
While it is impossible to relate loading/unloading conditions to traffic
flow by any simple formula, it is possible to generalize that the quality of
traffic flow is benefited by minimizing conflicts between street traffic and
service vehicles. Inasmuch as exhaust emissions relate directly to quality
of traffic flow, it is certain that minimizing these conflicts is a positive
step in reducing air pollution.
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4. Pedestrian Control --In downtown areas, where pedestrian flows are
large, special controls may be used to minimize pedestrian/vehicle conflict.
Streets with extremely high pedestrian utilization can be closed to vehicular
traffic, either permanently or during a portion of the day. In so doing, it
may be necessary to provide additional capacity elsewhere in the street
system. Plans of this type are becoming popular in many large cities.
At some locations it may be desirable to use barriers to control
pedestrian movement, channelizing and concentrating pedestrian crossings
at specific points. A barrier can be a permanent fence or posts with
connecting chains located near the edge of the sidewalk. Signs directing
pedestrians to the proper crossing locations should be mounted on or near
the barrier.
5. Traffic Operations Program to Increase Capacity and Safety (TOPICS) --
The U.S. Congress, recognizing that good transportation is vital to a
desirable urban environment, directed the Secretary of Transportation to
develop a program by which the Federal Government could assist cities
in alleviating their backlog of transportation needs. The result was the
^Traffic Operations P_rogram to_Increase C_apacity and Safety (TOPICS). The
p'urpose of this program is to obtain maximum efficiency and safety from the
existing major street network through a systematic application of traffic
engineering techniques. These traffic engineering treatments would not
include construction of major new facilities, but rather the application of
more sophisticated signal control, parking restrictions, lane widening,
turn-lane additions, and other minor redesign and channelization requiring
a minimum of new right-of-way. Although air pollution reduction is not an
objective of the program, it is an important byproduct of improved traffic flow.
Since TOPICS is not a particular operations policy, but rather a
collection of systematic traffic engineering techniques, many of the actions
already identified under freeway, arterial, and downtown operations can be
implemented as part of an areawide TOPICS program. Since Federal funds
3-18
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have been available in the program only since January 1969, it is impossible
to assess the impact of TOPICS on an urban area. However, the results of
a similar program in the British County Borough of Gateshead produced
the benefits summarized in Table 3.4.
Table 3.4. BENEFITS OF TRAFFIC MANAGEMENT
SCHEME, GATESHEAD9
Item
Traffic Volume entering
cordon
Total vehicle hours within
cordon
Vehicle miles traveled
within cordon
Average speed per vehicle
within cordon
Pedestrian accidents
Vehicle accidents
1965
Before
78,325
9, 250
109, 900
11.9
37
27
1968
After
82, 080
7, 166
123,700
16.3
30
21
Change, %
+ 5
-23
+13
+37
-19
-22
In spite of a higher number of vehicles and an even larger increase
in vehicle miles within the cordon, average vehicle speeds increased from
11. 9 to 16. 3 miles per hour and total vehicle hours were reduced. Thus
the reduced emissions per mile would more than offset the increased mileage.
The benefits to be gained by TOPICS in reducing air pollution emissions
are very significant. Thus TOPICS should figure importantly in the resource
allocation strategy of each city.
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TECHNIQUES FOR REDUCING POLLUTION CONCENTRATION
The utilization and design of highways can be effective in reducing
the air pollution concentrations in the ambient air. If peak-hour traffic
concentrations were reduced by distributing traffic over a larger area and
over a longer period of time, the air space available to disperse pollutants
would be greater. Also, good design can improve the operational charac-
teristics of the transportation system and thus minimize the concentration
of air pollution to which people, plants and structures are exposed.
A. Staggered Work Hours
A possible means of reducing peak period traffic volumes and congestion
is to spread the demand for travel over a longer time period, thereby reducing
the magnitude of the peak period demand. So doing will reduce vehicle-hours
in the system, attendant air pollution, and maximum concentration of
pollutants. Staggering the morning rush is particularly important because
the wind speed early in the day is low and the atmosphere is generally stable --
conditions that inhibit the dispersion of pollutants. Delaying morning travel
peaks would result in cleaner air generally because of both these characteris-
tics. Delaying the morning rush hour in Los Angeles by one hour would
reduce oxidant concentrations by 24 percent.
Staggered work hours was first used in the United States during
World War II, when approximately 60 cities used the idea to alleviate the
critical problem of mass transportation capacity shortage. All cases
achieved some degree of success; many cities reduced peak period travel
demand by as much as 30 percent. All major staggered-hour plans were
terminated after the war.
The most publicized plan for staggered work hours in recent years
has been in the lower Manhattan area of New York City. In April 1970 about
50. 000 persons employed by 45 firms and government agencies in lower
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Manhattan began a program of staggered work hours, shifting from the-
traditional 9:00 to 5:00 schedule, principally to a new 8:30 to 4:30 schedule.
As of April 1971, there were about 60, 000 people representing 70 private
firms and governmental agencies on the new schedule. Public response to
the project, which is being sponsored by the Port of New York Authority and
the Downtown-Lower Manhattan Association, has been overwhelmingly
,., n
favorable.
A significantly changed pattern in peaking characteristics was evidence'
as a result of the staggered hours project. Figure 3. 7 indicates the effects
at the Port Authority's Hudson Terminal for the afternoon peak. Vehicular
counts were taken at the Brooklyn Battery Tunnel and the Battery Parking
Garage. Little change has been observed as a result of staggered hours,
primarily because the number of participants thus far is but a small
proportion of total area employment.
8,000
6,000
VI
It
w
a
iU
4,000
2,000
I I
FEBRUARY 1970 - 23,691
OCTOBER 1970-
23,786
1,000 PASSENGER
REDUCTION
4:30
4:45
5:00 5:15
TIME (p.m.)
5:30
5:45
Figure 3.7. Effects of staggered work hours, Hudson Terminal
afternoon passenger volumes.11
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B. Roadway Concentrations
A number of studies have been made of the air pollution distribution
pattern (vertically and horizontally) from roadways to understand the
effects of highways on pollution in adjacent buildings. Frankfurt-am-Ma in
12
was the subject of an investigation on the time and space distribution of
carbon monoxide emission concentrations.
Figure 3. 8 shows the carbon monoxide concentrations on both the
leeward and windward sides of a roadway at heights of 3, 16, and 33 meters
12
above the roadway.
Figures 3. 9 and 3. 10 provide additional information on the decrease
of carbon monoxide concentrations with distance vertically and horizontally
13
from a roadway in relation to the pollution level at the roadway. Such
information is useful in deciding where to build a structure in relation to
the highway so that pollution will not exceed a safe acceptable level.
Similarly, the curve showing the decline of pollution with height above
the roadway can be useful in determining air-rights construction.
14
A study was also made of the concentrations of CO resulting from
vehicles elevated above ground level on open structure. Each isopleth
(line of equal value) in Figure 3. 11 shows the recorded concentrations of
carbon monoxide emissions in parts per million for vehicles at an elevation
of 10 feet. The ambient level was presumed to be zero feet. Emissions
are a function of vehicular elevation and horizontal distance from the edge
of the roadway in feet. (Elevated roadways on solid fill cross-sections
would be expected to exhibit different characteristics. )
C. Cross-Sections
Concentrations of nitrogen oxides, hydrocarbons, and carbon monoxide
were measured at various levels above five different types of highways,
including an expressway with adjacent structures nearby, an expressway
3-22
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18
16
o
"
5
00
3'°
t-
I-
Leeward Side
meters
meters
0 400 800 1200
VOLUME, vehiclei/hour
(Wind speed approximately 2 meters/second)
1600
400 800
VOLUME, vehicles/hour
(Wind speed approximately 2 meters/second)
1200
1600
Figure 3.8. Carbon monoxide concentrations depending
upon traffic volumes.12
3-23
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100 .«*-
Pollution Lovel at Roadway
. so
o
I
60
. 40
20
8
Ambient Pollution Level
20 40 60 80 100 120 140 160 180
DISTANCE TO EDGE OF ROADWAY, feet
Figure 3.9. Pollution level versus distance to edge of roadway.
13
100
80
60
40
20
Pollution Level at Roadway
o
8
20 40 60 80
HEIGHT ABOVE ROADWAY, feet
100
Figure 3.10. Pollution level versus height above roadway.
13
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20-
8ASE
15-
LU
IU
§ 10-
5-
5.5
100
200
300
400
500
DISTANCE FROM ROADWAY, feet
NOTE. Lines shown on this diagram are septette for
carbon monoxide concentrations (parts per million
as shown).
Figure 3.11. Carbon monoxide concentrations for a highway design.
14
without these joint development structures, and an expressway boulevard.
The average concentration on the four lanes for the expressway without
joint development structures was 39 ppm; a similar concentration for a
boulevard expressway was 49 ppm, an increase of 26 percent.
Efforts to reduce air pollution by changing highway design may not
be aimed as much at reducing total emissions as at reducing concentrations
at various significant distances from the roadway. Emissions can be
reduced by the design of the highway itself, or by regulating the relationship
between the highway and the adjoining land use.
In a study soon to be released, the General Electric Company performed
comprehensive air quality monitoring in areas adjacent to highways. The
results of this study should substantially improve our knowledge of the basic
factors related to air quality and automobile emissions. In addition, the
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District of Columbia Department of Highways is sponsoring a project to
investigate the concentrations of carbon monoxide adjacent to freeways.
D. Elevated, At-Grade, Depressed Roadways
The decision to design a new highway as an elevated, at-grade or
depressed facility can have a major effect on its air pollution impact.
Arguments in favor of depressing highways in urban areas usually
point to reduced neighborhood disruption and noise. These arguments may
be valid, but depressing a highway affords little opportunity for local wind
currents to disperse the emissions. Thus, the motorists traveling on a
depressed highway, as well as persons in adjacent areas, may be exposed
to unusually high concentrations.
Elevated highways, on the other hand, promote rapid dispersal of
pollutants away from the motorist. By virtue of being elevated, they are
more exposed to wind currents which transport as well as disperse pollutants.
While this pollutant dispersal represents a positive factor for the motorist,
the highway design engineer must pay close attention to how it affects
adjacent land uses. It may benefit the motorist to have all the pollutants
transported away from an elevated highway, but if they are transported
directly into an adjacent building the result may be a serious detriment
to the occupants. In this regard, the highway designer would do well to
consult with local meteorologists to determine the micro-climate of the
desigii corridor. Needless to say, the aesthetic aspects and other environ-
mental impacts of elevated highways have to be considered.
TECHNIQUES FOR REDUCING AUTO TRAFFIC
Any program that focuses exclusively on improving traffic flow to
reduce air pollution is likely to be self-defeating. The objective of an
effective approach to reducing pollution related to the automobile must be
to reduce auto travel. Currently, the best ai preaches to this objective are:
3-26
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1. To improve public transportation service.
2. To juxtapose land uses in a manner to minimize the
requirements for vehicular travel.
3. To regulate the use of automobiles.
A. Transit Operations
The modal choice decision is influenced by the myriad characteristics
of competing modes. Of particular importance are the relative travel
time by the best transit and auto routes, the relative cost to the passenger
by transit and auto, and the relative service provided by transit and auto.
1. Bus Lanes on City Streets — A measure that can be taken to improve
the attractiveness of transit relative to the auto is to provide reserved
transit lanes on city streets. This is rarely easy to do because of the road
space thus reserved but usually not used to capacity, and the problems of
providing for turning movements and of enforcement. Nevertheless a
number of exclusive bus lanes are in existence and show good results. Both
speed and reliability of buses benefit from exclusive lanes, particularly if
signals are timed to facilitate their movement.
In corridors with high transit volumes, overall traffic flow may be
improved, in addition to improving transit service.
2. Bus Lanes on Freeways -- The speed and reliability of transit service
can be substantially improved by providing exclusive bus lanes on urban
freeways.
There are several operational projects in the early implementation
stage. Among these are the Shirley Highway (1-95) project from Northern
Virginia to Washington, D. C. Buses on the Shirley Highway use the
reversible lanes in the freeway median over a distance of nearly 9 miles
in both directions. With the completion of temporary lanes and the addition
of 30 new buses in the spring of 1971, express routes were carrying nearly
7, 500 passengers on 160 inbound runs during the morning peak by September
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1971, Buses save 30 minutes over automobiles for the same portion of the
Shirley Highway trip. There is insufficient data to determine the impact
of the bus lane on travel in the corridor; however, a 3-year Urban Mass
Transportation Administration demonstration and evaluation project is
in progress.
Another operation, the Blue Streak Demonstration Project, is being
tested in Seattle. This project consists of special buses using the Seattle
Freeway reversible roadway in the peak direction over an 8 mile distance
and an exclusive on-off ramp in the downtown area. A 475-car parking lot
was constructed at the end of the line. Within a month the lot was filled,
with many additional vehicles parked illegally. In summary, the public
response has been very favorable. Further evaluation of the project is
underway at the time of writing this Guide but it will be necessary to expand
the park-ride capacity in order to determine the full impact of the high-speed
bus service.
3. Qne-Way Streets with Two-Way Buses -- Bus operators generally are
of the opinion that one-way streets have an adverse effect on transit rider-
ship. Riders may have to walk farther and in any case can no longer alight
from and board buses on the same street. A one-way street system may
also have the effect of lengthening bus routes and travel time. By providing
a reverse-direction exclusive lane it is possible to retain two-way bus
operation on a one-way street, with potentially higher ridership than would
be obtained if buses ran on two one-way streets instead. There has been
limited .application of this technique, but it would appear to merit trial
where appropriate conditions exist.
4. Park-Ride, Kiss-Ride -- Because of the difficulty of providing effective
bus service in low density residential areas, one of the most promising
transit improvements is the provision of park-ride and kiss-ride facilities
in conjunction with express bus or other transit services. A park-ride
facility includes a parking lot and express bus ~;:op; a kiss-ride facility is
3-28
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a lane set aside for autos to discharge or load passengers without impeding .
traffic flow. Commuters are thus able to travel by car in less congested
areas where bus service would involve a long walk or wait (or both), but use
transit for the portion of the trip where traffic is more difficult and parking
expensive. Seattle's Blue Streak and Cleveland's rapid transit system are
examples of the effective use of this technique. Completion of the Blue
Streak evaluation will indicate the potential for reduced vehicular traffic
and attendant air pollution.
5. Service Improvements and Cost Reductions -- The effect that transit
operating policies have on the demand for auto trips is fundamental in any
effort to reduce auto travel through transit improvement. One of the most
ambitious efforts to identify the relationship between transit and auto demand
16
was a study performed for the U.S. Department of Transportation, using
data from the Boston metropolitan area. Based on origin-destination data
collected in 1963 and 1964, an econometric model of urban passenger travel
demands was developed using constrained multiple regression techniques.
The model measured the relationship between the number of trips by purpose
and mode and the socio-economic and land use variables that give rise to
travel demand. The major quantitative outputs of the study were demand
elasticities and cross-elasticities by mode and trip purpose.
Transit demand was found to be relatively inelastic with respect to
fare changes (i.e., a 1 percent increase in fare decreased ridership less
than 1 percent), indicating that transit usage would not be markedly increased
17 1R
by reducing fares. This finding has been corroborated by numerous studies '
of transit patronage before and after fare increases, although instances of
greater than 1. 0 elasticity (representing a more than proportionate loss of
riders in response to fare increases) have been seen recently,
A second major conclusion was that most of the cross-elasticities
are very low or negligible. The low cross-elasticities indicate that it is
difficult to reduce the number of auto travelers by improving transit service
or lowering fares. The demand for auto trips was found to be more sensitive
-------
to reductions in transit travel times than to reductions in fares. It was
estimated that the institution of a free transit system in Boston would result
in a 4 percent areawide reduction in automotive exhaust emissions.
The model reflected the fact that several elements are included in the
effect brought about by a change in service of a travel mode. For example,
a transit fare reduction will attract additional trips that consist of trips not
previously made at all, and trips diverted from auto. The trips diverted
from auto may not be typical auto trips, in terms of such factors as auto
occupancy. The reduction in number of auto trips may in part be offset
by new auto trips, induced because of road capacity vacated by the diverted
trips. All of these elements are influenced by the cost and service aspects
of the available modes. There is evidence that the elasticities are non-linear
and may also vary from city to city in ways not fully predictable. Thus
the findings described here, although generally indicative, do not apply
specifically.
In summary, it appears that the modal choice decision is more a factor
of the socio-economic characteristics of the traveler than of relative costs
and travel time. Nevertheless, changes in service and fares can have .useful
impact in attracting trips to transit from auto, thereby reducing the amount
of auto travel and resultant emissions. There is a greater likelihood of
inducing the auto traveler to use transit by improving the level of service
(travel time including waiting and walking) than by reducing fares. The
greatest diversion is likely to occur by increasing frequency, reliability,
and accessibility of service. Consequently, efforts to subsidize transit
operations might best be directed toward improving service rather than
reducing fares.
B. Regulation
There are several governmental policies that go beyond the normal
pricing policy in that they regulate traffic bv writ. Although they may be
difficult to implement in the political framework of decision making, there
3-30
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can be no doubt about their effectiveness in reducing traffic congestion and
air pollution. In any event, they may be useful measures to bear in mind
for possible implementation during emergency air episodes.
1. Parking Bans -- One such measure is to prohibit parking in downtown
areas -- thereby necessitating a switch to a transit mode on the part of
commuters. As in the case of a parking tax, through motorists would be
unaffected if not encouraged. A similar proposal, though less severe, is
to limit the number of downtown parking spaces to a certain "acceptable"
number. The impact of either measure may be in part to redistribute travel
to locations where parking is available. If this were to occur, there would
be a corresponding redistribution of pollution at some detriment to the new
locations.
2. Auto-Free Zones — Banning vehicles completely in certain parts of a
city has been tried in many locales. Tokyo has banned cars from 122 of its
busiest streets on Sundays, the busiest shopping day in Japan; air pollution
levels were -cut in half. New York City took similar action, resulting in
as much as a 90-percent reduction in carbon monoxide levels on some auto-
less streets. Unfortunately, such a ban tends to raise traffic levels,
congestion, and attendant pollution levels in adjacent areas. When an auto
ban was implemented in a section of Rome, disastrous traffic jams and air
pollution were created all around it. A similar ban in Florence, however,
had favorable results. A requirement in implementing auto-free zones,
therefore, is to plan carefully for traffic movement at the periphery of the
zone.
An interesting technique is being tried in Gothenburg, Sweden, where
planners found that 30 to 40 percent of downtown traffic was through traffic.
The solution was an old planning idea with a new twist. A ring road was
constructed around the center city -- an old planning idea. The new twist
was to erect barriers dividing downtown into quadrants so that cars could
-------
no longer drive through the central business district. On Ostra Hamngatan,
a street which still has the most intensive pedestrian exposure in the city,
the CO content in the air has been reduced from about 65 to 5 ppm.
3. Gasoline Rationing -- Another method of regulating vehicle travel in
urban areas is to ration gasoline. Basically, each vehicle would be alloted '
a certain amount of gasoline per unit time. It would be up to the vehicle
owner to limit his trips to those that he could accomplish within his gasoline
allotment.
Although it would be politically difficult to implement, gasoline rationing
would be effective in reducing automotive emissions. An advantage of the
idea is that it might have less tendency to redistribute trips, a characteristic
of localized measures.
4. Idling Restrictions -- Emission characteristics during acceleration,
and idling have been discussed. The concentration of carbon monoxide in
exhaust gases of an idling vehicle is nearly twice that of a cruising vehicle.
Thus, any regulatory measures aimed at restricting vehicle idling times
would be a positive step toward cleaner air. While it would be difficult to
construct and enforce a useful regulation to limit idling, it is conceivable
that a public information program could achieve driver cooperation in
shutting off auto engines wherever long delays are anticipated or encountered.
Stockholm, Sweden has initiated a program which prohibits idling or
warming of automobile engines in excess of 3 minutes while the vehicle is
parked. Drivers are informed of this prohibition by signs and by printed
notices placed on the windshield. Violations are punishable by law.
5. Four-Day, Forty-Hour Week -- Although the 4-day, 40-hour work
week presently encompasses a very small fraction of the labor force in
the United States, it appears to be gaining in popularity at an increasing
rate. At the latest count, over 100 firms around the United States had
switched to the 4-day week in one form or another. Some have adopted
a 36-hour week with 9-hour days.
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The possible effect of widespread implementation of the 4/40 concept
on traffic volume, congestion, and air pollution is difficult to predict,
although indications are favorable. One effect of lengthening the work day
would be similar to the staggered work hours concept: peaking of traffic
demand would be reduced by an amount dependent on the number of persons
changing over to 4/40. In addition, on 1 or more days, the total number
of work trips would be significantly reduced. This reduction would have a
primary pollutant-reducing effect because of trips no longer made; a
secondary effect is that trips made would be at improved traffic flow.
There is little knowledge of the overall effect on trip making patterns
that would result from a substantial changeover to 4/40. A new weekly
schedule may change the entire trip generating character of an area. In
particular, there might be greater overlap between downtown shopping
trips and work trips.
The idea generally seems very promising; progressive urban areas
might consider promoting 4/40 on the basis of expected improvements in
air quality.
C. Pricing Policy
One way to reduce emissions is to impose operating penalties or
disincentives, which would place special charges on traffic using congested
roads. The underlying theory upon which road pricing schemes are based
is rooted in classical micro-economic techniques. The vehicular volume
on a particular roadway is interpreted as the point of equilibrium between
the demand and supply functions of the given roadway. The demand function
represents the number of trips that would be made at a particular price.
(To the economist, the term "demand" has no significance unless a price
is stated. ) The "price" should include not only money cost, but also a
measure of travel time (which can be expressed in monetary terms),
comfort and convenience, and other pertinent factors. These can all be
3-33
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reduced to a common monetary denominator and included in the ' price of
travel.
The supply function, on the other hand, expresses the price per trip
as a function of the number of trips made. (Note that this supply function
is different from the typical industry supply curve used in the theory of the
firm: it is a price/volume curve where the price is the user cost of a trip'
as perceived by travelers. Thus, as the traffic on a highway increases,
travel time increases, operating costs increase, and correspondingly the
"price" increases as shown in Figure 3. 12.
o
1C
V - NO-TAX POINT OF EQUILIBRIUM
V •= TAX-ADDED POINT OF EQUILIBRIUM
SUPPLY
DEMAND
VOLUME, vehicles per unit time
Figure 3.12. Supply-demand relationship*.
Imposing a uniform tax effectively creates a new supply function.
Actually, a change in price structure redistributes income among consumers
and causes a shift in the demand curve. In this instance, any tax that results
in reducing the number of current users may induce new users to begin using
the roadway. For example, a highway toll ma^, reduce the number of low-
3-34
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income, drivers, while the resulting reduction in congestion will cause more
high-income drivers to use the facility. But assuming no demand shifts, the
new point of equilibrium will be at a volume V1 . Thus, the imposition of a
uniform tax results in a volume decrease of (V - V1), allowing the facility
to operate at a higher level of service in terms of speed.
Although this is an oversimplification of road pricing policy, it is
sufficient as a basis for discussing pricing mechanisms as a means of
reducing traffic congestion. The various pricing policies discussed below
may prove very useful in reducing traffic congestion, although there are
problems involved in their implementation.
Road-pricing policies can adversely affect the economic growth of
a region. A study of the Hampton Roads area of Virginia indicated that
pricing policies on river crossings could have a significant impact on
employment in the region. These effects might be offset if uniform
restraint measures were used over a wider area.
Measures that discourage auto travel to a downtown area may adversely
affect retail activity; but, time-selective parking policies should help to
offset such effects. Improvement of mass transit also will be important.
Another major objection to congestion pricing is the claim that it
is economically regressive. Most likely to be priced off the roadway are
the low-income motorists. Pricing them off the road may also mean
pricing them out of a job if no adequate alternative mode of transportation
exists. Rebates to those of low income might be an appropriate way to
alleviate this problem. Providing good transit service is equally relevant.
These problems are significant but the willingness of the public to
grapple with them is growing. The control of parking charges has had
some acceptance, and is being seriously considered for the new Metro
system in Washington, D. C. Road pricing has been very closely studied in
Great Britain, to the extent of devising a "black box" that can be installed
3-35
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in an automobile to record road-user charges. A current study in Venezuela
is examining the applicability of road pricing there. Germany taxes engine
displacement; Bermuda limits maximum size; and Great Britain heavily
taxes automobiles and motor fuels.
1. Parking Policy -- One way to implement a pricing policy is to
regulate parking charges in congested areas. Parking charges could be
maintained uniformly higher than the market rate, thereby reducing the
number of trips made throughout the day. Alternatively, parking charges
could be regulated under a variable charge strategy according to time of
day or location. For example, high all-day parking rates would discourage
commuting by automobile.
In Canberra, Australia, a theoretical simulation study showed that
increased parking costs would reduce vehicular travel by increasing car
19
occupancy and transit usage. This reduction in travel would reduce the
air pollution generated by vehicles. Figure 3. 13 shows that adding a $1. 00
parking cost would reduce air pollution in Canberra by approximately 30
and 40 percent in the town centers and central area, respectively.
so
a*
1
LU
O
s
DC
u
X
111
O
LU
cc
.25 .50 .75 1.00
9-HOUR PARKING COSTS,$ (Australian)
Figure 3.13. Effects of parking costs on vehicular air pollution emissions.
3-36
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Although some benefits might be realized from taxing parking space
in congested areas, any restraint based on parking restrictions alone will
affect only those who live and work in the particular area. The restraint
will not affect through traffic, which may even increase its use of street
capacity vacated by autos no longer parking.
2. Road User Tax -- Another pricing measure that could be used to
discourage auto trips is to implement a road-user tax. Charging autos to
travel through the dense city center would reduce traffic volume considerably.
Such a plan could be implemented by charging a toll for vehicles entering a
central cordon area. Other means of collection, such as a daily pass displayed
within the vehicle, have been proposed. As a means of implementing a pricing
policy, a road user charge has the advantage of being applied to moving
vehicles, not merely those that park in the area. Like higher parking
charges, however, the measure is selective toward those in a particular
area and therefore politically difficult to implement.
3. Gasoline Tax -- Increasing gasoline taxes as a means to discourage
auto trips into central areas has been suggested from time to time. Although
there is no information to substantiate any conclusion in this area, it does
appear that gasoline taxes would affect auto travel. Depending on the amount,
the tax could reduce trip making or encourage the use of more economical
autos. The British tendency toward small-displacement engines, which
taxes motor fuels heavily, is a case in point. The tax would have to be
applied over a wide region in order to discourage motorists from going to
outlying areas to buy their gasoline. Even more important, the gasoline tax
is not a direct out-of-pocket cost which the motorist must bear each time
he makes a trip. Therefore, his sensitivity to a gasoline tax would not be
as great as his sensitivity to a more direct toll system.
3-37
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4. Car Pool Incentives -- Typical urban-area auto occupancy for travel
to work is 1. 2 to 1. 3 persons per vehicle. Through car pooling, the same
number of employees could be accommodated in far fewer autos. Pricing
policy could be used to provide incentives for car pooling. Tolls could be
higher for low-occupancy vehicles. In particular, such a scheme might
prove worthwhile for cities where a large percentage of commuter traffic
utilizes bridges and tunnels where tolls already exist or could be implemented
easily. Note that uniform but higher tolls also would encourage car pooling.
D. Planned Unit Development
The evolution of planned unit development and new towns over the
past decade is encouraging to the air pollution abatement agencies. Planned
unit development brings various land uses together on a neighborhood level;
the new town ' concept does so on a town basis.
Locating residential areas near shopping and employment centers
minimizes the need for vehicular travel by locating major trip origins and
destinations near to each other.
Although their impact on air quality is long term, planned unit develop-
ments should be actively promoted by traffic engineers and air pollution
control officials. The Urban Planning Guide will explore this concept in
greater detail.
3-38
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APPENDIX A
INTRODUCTION TO AIR POLLUTION
-------
APPENDIX A
INTRODUCTION TO AIR POLLUTION
Recent legislation requires that the transportation professional
consider the air pollution impact of his plans. To do so, he must become
familiar with air pollution terminology and characteristics. The purpose
of this appendix is to provide this information.
TYPES OF POLLUTANTS AND THEIR SOURCES
A. Classification of Pollutants
Air pollutants are commonly classified as either gaseous or particulate.
Gaseous pollutants behave much like the air itself; they do not settle out.
Particulate pollutants may be either solid or liquid, and their performance
in the atmosphere varies according to chemical composition and size:
heavier particles settle close to the point of emission; and smaller, less-
dense particles travel great distances. Urban aerosols, formed by the
grinding or atomization of solids and liquids, are particulate matter ranging
-7
in size from approximately 6 x 10 to 1 micron; they include mist, smoke,
dust, fumes, and spray.
Air pollutants also can be categorized as either primary or secondary.
A primary pollutant is emitted directly into the atmosphere and initially
retains its form as emitted. A secondary pollutant is formed in the atmosphere
from reactions that may be chemical, photochemical, or biological.
A third way of classifying pollutants is by chemical composition --
either organic or inorganic. Many of the most common pollutants -- the
oxides of carbon, nitrogen, and sulfur -- are inorganic; organic pollutants
include hydrocarbons, aldehydes, and ketones.
A-l
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To classify an air pollutant properly all three classifications should
be used; for example, carbon monoxide is a primary, inorganic, gaseous
pollutant.
B. Units of Air Pollution Measurement
Air pollutants can be quantified in several ways: on the basis of
emissions from sources, according to concentrations in the ambient air,
or according to rates of exposure.
The source strength of air pollutants can be quantified in units of
mass or weight per unit volume, for example, grams per cubic meter of
air or pounds per cubic foot. Emissions may also be stated in terms of
weight per unit time, weight per unit weight of product, weight per BTU,
weight per unit area for area sources, or mass per unit distance for vehicles.
Concentrations of pollutants in the ambient air are normally reported
as mass or weight per unit volume of air, such as micrograms per cubic
meter. The unit parts per million (ppm), although used, is being discontinued.
Settleable particulate matter sometimes is expressed in terms of tons per
square mile per month or the currently recommended grams per square meter
per month; and suspended material as micrograms per cubic meter or Coh's
(Coefficient of Haze), a unit of measurement of visibility interference.
Also of concern in the expression of concentrations of air pollutants
is the quantity and duration of exposure experienced by plants, animals, or
humans. Called the dosage or rate of exposure, units indicate both concentra-
tion and time involvement, with levels stated in terms of micrograms per
cubic meter either per hour, 8-hour period, day, or year. In many cases,
the average concentration over a given period of time is of concern; in
other cases, the maximum concentration is more important.
When reviewing regulations or statements concerning concentrations
of air pollutants, it is important to understand the units used; that is, whether
they relate to the ambient air concentrations, to emissions, or to exposure
dosages.
A-2
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C. Classification of Sources
Pollutants emitted to the air in greatest abundance are carbon monoxide
(CO), oxides of sulfur (SO ), oxides of nitrogen (NO ), hydrocarbons (HC),
A
and particulate matter. Emission inventories of these five pollutants are
commonly divided into five source categories: transportation, fuel combustion
in stationary sources, industrial processes, solid waste disposal, and
miscellaneous. Nationwide emissions by category, presented in Table A. 1,
indicate that carbon monoxide is the major pollutant by weight, and that
transportation activities are the major carbon monoxide contributor.
Emissions of urban origin from stationary combustion and transportation
activities, account for greater than 75 percent of the total emissions in these
five pollutant categories. The motor vehicle is a major contributor to air
pollution. It contributes approximately 92 percent of the total transportation
carbon monoxide, about 50 percent of the hydrocarbons, and 40 percent of
20
the nitrogen oxides.
VARIATIONS IN AIR POLLUTION CONCENTRATIONS
Variations in pollutant concentration at or near ground level are a
function of both meteorological parameters and emissions, both of which
vary in time and space. Both fluctuate from place to place according to
daily and annual patterns; the latter also exhibit weekly variations. Thus,
pollutant concentrations are a function of location, time of day, day of the
week, and season of the year.
A-3
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Table A. 1. ESTIMATED EMISSIONS OF AIR POLLUTANTS
BY WEIGHT, a NATIONWIDE, 196921
Source
Transportation
Fuel combustion in
stationary sources
Industrial processes
Solid waste disposal
Miscellaneous
Total
CO
111.5
1.8
12. 0
7.9
18.2
151.4
Particulates
0.8
7.2
14.4
1.4
11.4
35.2
SO
X
1.1
24.4
7.5
0.2
0.2
33.4
HC
19.8
0.9
5.5
2.0
9.2
37.4
NO
X
11.2
10.0
0.2
0.4
2.0
23.8
Q
In millions of tons per year.
A. Variations According to Location
Variations according to location are the natural product of non-uniform
distribution of pollution sources; for example, freeway versus center city
traffic, and the random movements of air and weather patterns (rain and fog).
Figures A. 1, A. 2, and A. 3 illustrate significant variations in pollutant
concentrations (in this case, carbon monoxide) as they relate to location in
each of three large urban areas across the nation.
The many meteorological observations accumulated over decades
permit a fairly reliable estimate of the air pollution potential in various
sections of the United States. Regions with a clean sweep of winds within
the major storm tracks are least likely to develop high pollution conditions;
regions dominated by stagnant air masses and light winds are most likely
to experience high pollution conditions.
A-4
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B. Variations by Time Periods
Space heating and solar radiation are the two major factors influencing
seasonal variations in air pollution levels. Secondary pollutants, such as
photochemical oxidants, generally are worst in the late summer or autumn
when optimal combinations of solar radiation, temperature, and atmospheric
stagnations coincide.
Weekly variations in carbon monoxide are a function of the different
transportation and activity patterns associated with weekdays, weekends,
22
and holidays. A study revealed a distinct 20 percent decrease in the
average carbon monoxide concentrations during the weekend compared to the
higher weekday levels. In urban communities, where there are many week-
end travelers, the reduction is considerably less.
In general, meteorological conditions at night encourage the accumu-
lation of pollutants; those in the day encourage their rapid dispersion. Diurnal
variations in carbon monoxide concentrations are illustrated in Figures A. 1,
A. 2, and A. 3; Figure A. 4 shows diurnal variation in concentrations of
8
x
o
o
co
tc.
o
LODGE-FORD FREEWAY INTERCHANGE
GRAND CIRCUS PARK
GM TECHNICAL PARK. WARREN
2 -'
M
TIME OF DAY
Figure A.1. Hourly carbon monoxide concentrations on weekdays in Detroit area.'
22
A-5
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I
LU
Q
X
o
o
o
CD
tr
M
8 10 M
TIME OF DAY
Figure A.2. Hourly carbon monoxide concentrations on weekdays in New York area.
22
I
x
o
03
EC
16
14
12
10
PICO BOULEVARD
HARBOR - SANTA MONICA
FREEWAY INTERCHANGE
SANTA MONICA
MONROVIA
.AM
I
-PM.
I
M
10
10
M
TIME OF DAY
Figure A.3. Hourly carbon monoxide concentrations on weekdays in Los Angeles area. 22
A-6
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Z in
0.20 -
0.15
0.10
0.05
0.00
SEPTEMBER 9. 1963
20
15
10
I
cn
z
tu
U
§
o
12 2 4 6 8 10 12 2 4 6 8 10 12
M N M
(AM) HOUR OF DAY, EST
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METEOROLOGY
Meteorological and topographical conditions in some areas favor the
accumulation of pollutants. Lighter particles and gases as emitted by
vehicles diffuse only as rapidly as meteorological conditions permit. During
this diffusion, the nature of the pollutants may be changed by natural, physical
or chemical processes, such as solar radiation, rain, fog, and interaction
with the normal constituents of the atmosphere. Typical examples are the
oxidation of nitric oxide to nitrogen dioxide and the photochemical action
that forms oxidants.
In a dry atmosphere, the adiabatic lapse rate (rate of temperature
decrease with increase in elevatipnKs 1 C per 100 meters (5.4 F per 1,000
feet). When the actual lapse rate is greater than this theoretical rate, a
parcel of air that begins to rise continues to do so and the atmospheric
condition is called "unstable. " If, however, the actual lapse rate is less
than the adiabatic rate, the surface air remains near the surface and the
atmospheric condition is called "stable. "
An increase of temperature with altitude (an inversion) can occur at
any time, but is most common during the night arid early morning. An
inversion acts as a lid; it separates layers of air and prevents polluted air
from rising. If an inversion is accompanied by low winds, a layer of highly
polluted air may build up over a broad area.
Three major forces -- wind, heating, and cooling — cause shifts
from stable to unstable conditions and back again. Wind, in addition to
horizontal motion, usually has vertical eddies and, since rapid vertical
air motions tend to be adiabatic, helps to establish an adiabatic lapse rate.
The sun, which heats the surface more than the air, increases the lapse
rate and, thus, contributes to instability. Conversely, at night the ground
loses more heat by radiation than the air does, tending to make the surface
cooler than the air layers above; this cooling contributes to stability.
Usually there is a daily cycle from stability to instability and back again.
A-8
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When the cycle is broken and the atmosphere remains stable for a prolonged
period of time, a serious accumulation of pollutants is possible.
High pollution potentials are generally favored by light winds and clear
skies which promote the formation of temperature inversions. A buildup
of high pollution concentrations in the central core of the cities then occurs
as the result of this inversion "lid" coupled with a near-surface air movement
toward the center city. This air flow is the result of the heat island effect
in which the asphalt and concrete city heats up and acts like a chimney,
drawing in cooler air from the surrounding areas.
High pollution potential is defined as a stagnating anticyclonic condition
which, coupled with the continued operation of several sources, is conducive
to the occurrence of high concentrations of pollution. As defined, the high
pollution potential refers to developing meteorological factors only. The
National Meteorological Center in Suitland, Maryland prepares daily 36-hour
alerts. This information, called Air Stagnation Advisories (ASA), is
available through U.S. Weather Bureau Stations. Being an objective system,
the method has its shortcomings, the greatest of which is the lack of individual
appraisal-and forecasting for each city based on its local meteorology, and
areal distribution of pollution sources. The local air pollution control office
can provide the necessary in-depth knowledge of a specific urban community.
Within the space of a few miles, micro climatic conditions may con-
siderably influence the effects of pollution. A detailed survey of the meteoro-
logical terrain is needed to assess variations in local conditions; this is
particularly advisable when planning future communities and industrial areas.
For example, it used to be a rule of thumb to locate industrial areas down-
wind of a settlement with respect to the prevailing wind direction. Unfortunately,
in many instances the wind at times of stagnation or near-stagnation conditions
may be quite different from the most frequent wind. In some cases, the slight
draft under those conditions may be entirely opposite to the prevailing wind,
thereby causing a more severe pollution condition than would have been
anticipated.
A-9
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SITE CONDITIONS AFFECTING DISPERSION
The city in a general sense may be considered a collection of micro-
climates. The pattern and profile of the air motion in the total atmosphere
over an urban area are modified, sometimes considerably, in each of these
microclimates by the spatial arrangement and character of buildings and
other structures, by surrounding vegetation, and by roadway configurations.
Superimposed on this is the air movement resulting from traffic flow. In
addition, the relative influence of each of these factors depends on the
magnitude of the background air movement and solar heating conditions.
Factors found to be dominant at higher wind speeds may decline in significance
at the lower wind speeds which present the greater potential for severe
pollution episodes.
A. Urban Heat Island Effect
The combined effects of topography and urbanization decidedly influence
the radiation, moisture, and temperature conditions of a city. These in
turn modify the wind flow patterns. In an urbanized region, vegetation is
replaced by a vast man-made environment resulting in changes in moisture
conditions which in turn alter the heat distribution. The air is heated by
multiple sources including industries, automobiles, space heating, and
solar radiation.
It has been estimated that the automobile is an important artificial
heat source in the street canyons of a city. Very heavy traffic in parts of
London, for example, add an estimated 8 F to the air temperature. Bach
calculated that for the built-up area of Sheffield, England, the annual artificial
heat generation is about one-fifth of the direct solar radiation received. The
ratio is one-third for Berlin. Particulate matter, a byproduct of most
artificial heat generation, is 5 to 25 times greater in the urban area than
in the rural area.
A-10
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Temperatures in the urban heat island have been found to be on the
order of 5-8 C greater at night than in the surrounding rural areas. Side-
walks, roads, and concrete buildings have relatively high heat capacities and
conductivities. The daytime heat storage is greater than for grass-covered
fields or forests. The lack of evaporational cooling from the dry building
surfaces increases the stored solar energy. After sunset, the stored
daytime heat is released from buildings and pavements resulting in air
temperatures and winds in the city higher than those occurring in the
c\ r*
surrounding country. Munn notes that the heat storage ability of a city
is believed to be the major factor of the heat island formation, he adds that
the city is a collection of microclimates each dependent upon the character
of a built-up area within the entire city.
The heat island effect is found to be maximum in late summer and early
autumn when the skies are clear and winds are light. Figures A. 5 and A. 6
illustrate the morning and evening air circulation and dispersion models in
a city and in the surrounding country under anticyclonic conditions.
300 -
. 200 -
u
D
3
t 100 -
CITY COUNTRY
Figure A.5. Urban circulation and dispersion after sunrise.25
A -U
-------
. 200 -
Q
t 100 -
WEAK GEOSIHOHHIC WIND
SSSrote.***
±mm?m
HEAT ISLAND ST^\:j^;
Figure A.6. Urban circulation and dispersion after sunset.25
B. Building Configuration
The orientation of a building with respect to the winds produces
significant distortions in the local wind pattern. The significance of the
flow distortions becomes clear when vehicular emissions exist within an
area surrounded by buildings. Air currents can trap pollution, confining
it close to the buildings. Pollutants emitted from building roof vents may
also become trapped. Hence, roadway vehicular emissions and emissions
from roof tops can be conveyed into windows, doorways, and air intake
systems.
As background wind speeds decrease, the effect of the vertical
temperature profile (lapse rate) increases and becomes a major controlling
factor in the atmospheric dispersion of vehicular emissions in the urban
street canyon.
A-12
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During periods of light winds and clear skies, air flow around buildings
is, to a great degree, the result of convective updrafts coupled with winds
flowing into the center of the urban heat island. The updrafts remove
pollutants from the area of the building more effectively than strong
horizontal winds if no inversion exists.
The upward dispersion of vehicular emissions is often restricted in
the early morning hours by the presence of a stable layer existing from the
ground to roof level. The pollutants are trapped in or below this layer.
This phenomenon is most pronounced in the walled street canyons of urban
centers.
Various building configurations and orientations alter the air flow
pattern considerably. Rows of tall buildings lining urban streets modify
the microclimate by changing the topography and general aerodynamic
boundaries. In these street canyons, the dispersion of the pollutants is
determined by the turbulent wake of the traffic, by the differential heating
of building tops and streets, and by the generalbackground air movement.
Wind speeds at street level may be only 40 percent of the wind speed above
the roofs of the buildings.
More open roadway planning with the buildings set back will alleviate
this canyon effect. While traffic volume along a roadway section has the
most direct relationship to emissions, the higher mid-afternoon wind speeds
are the most effective factor in reducing the urban street canyon air pollution
concentrations. This effect is gradually lost later in the afternoon as the
overall wind speeds start to decrease and traffic volume once again peaks.
C. Roughness Effects
As noted above, the background wind is also modified by the texture
and height of surrounding features: buildings, trees, grass, brush, and
streets. For example, as wind passes from an orchard to an open field,
the wake effect is similar in many ways to that behind a building. Within
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approximately one-quarter mile the original near-surface wind speed is
reestablished. There is an updraft in the air movement as it encounters
a rougher surface, such as a row of trees.
Thus, a wide tree-covered green belt along both sides of a major
traffic artery provides more rapid dispersion of vehicular emissions. In
an urban area, similar transitions can be arranged -- between roadway
and green belt, park and buildings, parking lots and streets, and low- and
high-rise buildings. The resulting turbulence can lead to more dispersion
and dilution.
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APPENDIX B
GLOSSARY
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APPENDIX B
GLOSSARY
Aerosol
Air pollution
Ambient air quality
Anticyclone
Arterial
At-grade roadway
BTU
Channelization
A dispersion cf solid or liquid particles of
microscopic size in gaseous media. Examples
are smoke, fog, and mist.
The presence of unwanted material in the air
in sufficient amount and under such circum-
stances as to interfere significantly with
comfort, health, or welfare of persons, or
with full use and enjoyment of property.
A physical and chemical measure of the
concentration of various chemicals in the
outside air. The quality is usually determined
over a specific time period (for example,
5 minutes, 1 hour, 1 day).
An area of relatively high atmospheric
pressure. In the northern hemisphere, the
wind blows spirally outward in a clockwise
direction.
A major through street, four lanes or more
with no (or only limited) access control.
Roadway which is at the same level with
adjacent land.
British thermal unit. A measure of heat,
Specifically, 1 BTU is the amount of heat
required to raise the temperature of 1
pound of water 1°F at or near 39. 2°F.
Facilitating the flow of traffic by separating
or regulating conflicting traffic movements
of intersections at grade by use of markings,
signs, raised islands, etc.
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Coh
Cordon area
Cross-elasticity
Depressed roadway
Diurnal
Downtown distribution
system
Dust
Elasticity
Elevated roadway
Emissions
Episode
Forced-flow conditions
Gas
Coefficient of haze. A unit of measurement
of visibility interference.
An area surrounded by an imaginary line at which
surveys are undertaken for traffic analysis.
The change in demand for one mode resulting
.from a change in the explanatory variables
of an alternative mode. (Compare with
elasticity.)
Roadway which is below adjacent land.
Daily, especially pertaining to actions or
events that are completed within 24 hours
and that .recur every 24 hours.
The local streets in the downtown area that
serve adjacent buildings and facilities.
A term loosely applied to solid particles,
predominantly larger than colloidal,
capable of temporary suspension in air or
other gases.
The percentage change in demand resulting from
a I -percent change in one of the explanatory
variables, everything else remaining constant.
(Compare with cross-elasticity.)
\
Roadway which is above adjacent land.
The total substances discharged into the air
from a stack, vent, tail pipe, carburetor,
or other source.
The occurrence of stagnant air masses during
which air pollutants accumulate, so that the
population is exposed to an elevated concen-
tration of airborne contaminants.
Roadway traffic flow above the capacity of
the roadway, usually bumper-to-bumper
stop-and-go traffic.
One of the three states of aggregation of
matter, having neither independent shape nor
volume, and tending to expand indefinitely.
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Geostrophic wind
Inversion
Major /minor direction
Microeconomic
Midblock frictional elements
Mode
Month
Peak traffic demand
People movers
Queue
Right-of-way
Smog
Wind that exists in a region approximately 300
to 1000 meters above the surface of the earth
and is generally not influenced by surface
friction. Its speed constitutes a balance of
the forces from the pressure gradient and
rotation of the earth.
A layer of air in which temperature increases
with height.
Applies to a roadway at those times when
traffic flow in one direction (major) is two
(or more) times the flow in the other (minor).
Usually occurs during morning and afternoon
rush hours.
The economics over a small section of the
total economy, usually referring to only a
small number of items.
Those traffic hinderanees causing delays in
traffic flow between intersections, such as
parked cars, pedestrian crossings, truck
loading zones, and driveways.
Method of transportation such as bus, auto,
walking, rapid transit, or taxi.
For reporting analysis of ambient air on
a monthly basis, results are calculated to
a base of 30 consecutive 24-hour periods.
That traffic flow on an individual street or
in an entire area which is the greatest.
Usually the peak traffic demand is considered
over a short period of time (15-60 minutes)
per day.
Moving walkways, escalators, small
automated cars on fixed routes, etc.
A standing or slow moving line of autos
or people.
The land occupied by a roadway.
A combination of smoke and fog. Extensive
atmospheric contamination by aerosols
arising partly through natural processes
and partly from human activities. Often
used loosely for any air contamination.
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Smoke
Solid-fill cross-section
Topography
Traffic assignment
Vapor
V/C ratio
Weaving
Weaving section
Year
Small gas-borne particles that are produced
by incomplete combustion, consisting
predominantly of carbon and other combustible
material, and present in sufficient quantity
to be detectable independently in the presence
of other solids.
An elevated section of roadway on earth fill.
The configuration of a surface, including its
relief and the position of its natural and
man-made features.
A modeling process whereby trips from all
origins to all destinations are assigned to specific
routes, based on travel time and other factors.
The gaseous phase of matter that normally
exists in a liquid Or solid state.
The ratio of volume, or number of vehicles,
using a roadway to the capacity of that roadway.
The crossing of traffic streams moving in
the same general direction, accomplished by
merging and diverging.
A length of roadway designed to accommodate
weaving: at one end, two roadways merge;
and at the other, they separate.
For reporting analysis of ambient air on a
yearly basis, results are calculated to a base
of 12 30-day periods.
B-4
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APPENDS
REFEEZNC]
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APPENDIX C
REFERENCES
1. EPA. Requirements for Preparation, Adoption, and Submittal of
Implementation Plans. Federal Register. 36:158, August 14, 1971.
2. U.S. Office of Management and Budget. Circular No. A-95. Revised
February 9 and July 26, 1971.
3. U.S. Congress, Senate. National Air Quality Standards Act of 1970.
91st Cong., 2ndSess., Rept. 91-1196, p. 2, 1970.
4. Ministry of Transport (Great Britain). Cars for Cities. Her
Majesty's Stationery Office. London, 1967.
5. EPA. Air Pollutant Emission Factors. Preliminary Document,
April 1971.
6. Cernansky, N. P. and K. Goodman. Estimating Motor Vehicle
Emission on a Regional Basis. Presented at APCA Meeting, June 1970.
7. Bellomo, S.J., R. B. Dial, and A.M. Voorhees. Factors, Trends,
and Guidelines Related to Trip Length, 1970.
8. Highway Research Board. Highway Capacity Manual. Special Report
No. 87, 1965.
9. Leonard, J. H. Benefits from TOPICS - Type Improvements. Civil
Engineering-ASCE, 41:2, pp. 62-66, February 1971.
10. Kauper, E. K. and C. J. Hopper. The Utilization of Optimum
Meteorological Conditions for the Reduction of the Los Angeles
Automotive Pollution. APCA Journal, X:246-250, June 1960.
11. Downtown-Lower Manhattan Association and the Port Authority of
New York. Staggered Work Hours in Lower Manhattan - First Anniversary
Report. April 1971.
12. Georgii, H. W., E. Busch, and E. Weber. Investigation of the Time
and Space Distribution of Carbon Monoxide in Frankfurt-am-Main.
Report No. 11 from Institute of Meteorology and Geophysics,
Frankfurt-am-Main University.
13. Tippets, Abbet, McCarthy, and Stratton. Air Rights Potentials in
Major Highways--Criteria for Joint Development. October 1969.
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14. Environmental Systems Laboratory. Environmental Analysis
Findings for Proposed 1-66 Through Arlington County (Virginia).
Sunnyvale, Calif. 1970.
15. Sturman, G. M. The Effects of Highways on the Environment.
U.S. Senate Committee on Public Works, May 1970.
16. Domencich, T. A. and G. Kraft. Free Transit. D. C. Heath and
Co., Lexington, Mass. 1970.
17. Lassow, W. Effect of the Fare Increase of July 1966 on the Number
of Passengers Carried on the New York City Transit System.
Highway Research Record No. 213, 1968.
18. Curtin, J. F. Effect of Fares on Transit Riding. Highway Research
Record No. 213, 1968.
19. Golenberg. M. and R. Keith. The Effect of Land Use Planning and
Transport Pricing Policies in Express Transit Planning. Highway
Research Record No. 305, 1970.
20. HEW, U.S. Public Health Service. Nationwide Inventory of Air
Pollutant Emissions, 1968. NAPCA Publication AP-73, August 1970.
21. The Mitre Corp. Environmental Trends: Radiation, Air Pollution,
Oil Spills. MTR-6013. May 1971.
22. Colucci, J.M. and C. R. Begeman. Carbon Monoxide in Detroit,
New York, and Los Angeles Air. Environmental Science and
Technology. 3:1, p. 41-47, January 1969.
23. Stern, Arthur C., ed. Air Pollution, Vol. 1, 2nd ed., Academic
Press, New York, 1968.
24. Brunner, F.A. and K. B. Schnell, Jr. Air, Pollution Patterns in an
Urban Street Canyon. Paper presented at ASCE National Environmental
Engineering Meeting, St. Louis, Missouri. October 1971.
25. Bach, W. An Urban Circulation Model. Arch. Met. Geoph. Biokl.,
Series B. 18:155-168, 1970.
26. Munn, R. E. Descriptive Micrometeorology. Academic Press.
New York, 1968.
C-2
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The following are not referenced to the text:
Beesley, M. E. and G. J. Roth. Restraint of Traffic in Congested Areas.
The Town Planning Review, 33:3, October 1962.
Carmody, D. J. Modesto's One-Way Streets: 2nd Year Report. Street
Engineering, 5:3, March 1960.
Chamber of Commerce of the United States. One-Way Business Streets.
Washington, July 1954.
Crocker, B. B. and K. B. Schnelle, Jr. Introduction to Air Pollution Control.
American Institute of Chemical Engineers, 1969.
Fisher, N. W. F. Automotive Air Pollution -- An Economic Analysis.
Pollution Control - Thirteen Autumn Forum, Economic Society of Australia
and New Zealand, Victorian Branch, May 11, 1971.
Gersten, M. C. and J. M. Kahan. Buses Get Exclusive Use of Median.
Civil Engineering - ASCE, 40:7, pp. 68-72, July 1970.
Halitsky, J. Gas Diffusion Near Buildings. Meteorology and Atomic
Energy, 1968. U.S. Atomic Energy Commission, Section 5-5, May 1969.
Hanna, S. R. Turbulence and Diffusion in the Atmospheric Boundary Layer
Over Urban Areas. Presented at Syracuse University. February 1970.
Highway Research Record No. 47: Traffic Congestion as a Factor in Road
User Taxation, 6 Reports. 1964.
I. B. M., The San Jose Traffic Control Project -- Final Report. 1967.
Institute of Traffic Engineers. A Report of Technical Committee 3-D on
Reserved Transit Lanes. Traffic Engineering, 29:10, pp. 37-40, July 1959.
Institute of Traffic Engineers. Traffic Engineering Handbook. Washington,
1965.
Kennedy^ N., J.H. Kell, and W. S. Homburger. Fundamentals of Traffic
Engineering. Institute of Transportation and Traffic Engineering, Berkeley,
California, 1966.
Magill, Pi L., R. F. Holden and C. Ackley. Air Pollution Handbook.
McGraw-Hill Book Company, Inc., New York, 1956.
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McDermott, J. M. Operational Effects of Automatic Ramp Control on
Network Traffic. Highway Research Record Number 202, 1967.
Myers, S. Fail Safe Planning To Control Automotive Air Pollution. National
Planning Conference of the American Society of Planning Officials, New
Orleans, Louisiana, 1971.
On the Way to a Four-Day Week. Time. March 1, 1971.
Poor, R. 4 Days 40 Hours. Bursk and Poor Publishing, Cambridge,
Massachusetts, 1970.
Roth, G. J. An Economic Approach to Traffic Congestion. The Town
Planning Review, 36:1, April 1965.
Russell, G. L. Ramp Control on Freeways in California. Highway Research
Record Number 279, 1969.
Santerre, G. L. An Investigation of the Feasibility of Improving Freeway
Operation by Staggering Working Hours. Texas Transportation Institute,
January 1967.
Scorer, R. Air Pollution, Pergamon Press, Ltd., London, England, 1968.
Smith, Wilbur & Associates. Motor Trucks in the Metropolis. August 1969.
Smith, .Wilbur & Associates. The Potential for Bus Rapid Transit, prepared
under commission from Automobile Manufacturers Association, February 1970.
Voorhees, Alan M. & Associates, Inc. and Hammer, Green , Siler Associates.
The Hampton Roads Joint Transportation Study. October 1970.
Voorhees, Alan M. & Associates, Inc. Feasibility and Evaluation Study of
Reserved Lanes for Buses and Car Pools. Prepared for U.S. Department
of Transportation, January 1971.
Wallace, McHarg, Roberts, and Todd and Whittlesey, Conklin, and Rossant
and Alan M. Voorhees & Associates, Inc. The Lower Manhattan Plan.
Prepared for the New York City Planning Commission.
Wilshire, R. L. The Benefits of Computer Traffic Control. Traffic
Engineering, 39:4, April 1969.
Wohl, M. and B. Martin. Traffic Systems Analysis for Engineers and
Planners. McGraw-Hill, New York, 1967.
U.S. Department of Health, Education and Welfare. Air Pollution Engineering
Manual, 1967.
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