EPA-450/3-74-003-d
October 1973
VEHICLE BEHAVIOR
IN AND AROUND
COMPLEX SOURCES
AND RELATED COMPLEX
SOURCE CHARACTERISTICS
VOLUME IV -
PARKING FACILITIES
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air aiid Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-74-003-d
VEHICLE BEHAVIOR
IN AND AROUND
COMPLEX SOURCES
AND RELATED COMPLEX
SOURCE CHARACTERISTICS
VOLUME IV - PARKING FACILITIES
by
Scott D. Thayer
Geomet, Inc.
50 Monroe Street
Rockville, Maryland 20850
Contract No. 68-02-1094
Task Order No. 3
EPA Project Officer: Edwin Meyer
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, N. C. 27711
October 1973
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This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers. Copies are
available free of charge to Federal employees, current contractors
and grantees, and nonprofit organizations - as supplies permit - from
the Air Pollution Technical Information Center, Environmental Protection
Agency, Research Triangle Park, North Carolina 27711, or from the
National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22151.
This report was furnished to the Environmental Protection Agency by
Geomet, Inc. , 50 Monroe Street, Rockville, Maryland, in fulfillment
of Contract No. 68-02-1094. The contents of this report are reproduced
herein as received from Geomet, Inc. The opinions, findings, and con-
clusions expressed are those of the author and not necessarily those
of the Environmental Protection Agency. Mention of company or product
names is not to be considered as an endorsement by the Environmental
Protection Agency.
Publication No. EPA-450/3-73-003-d
11
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ABSTRACT
The report presents a general methodology for interpreting parameters
which characterize a complex source into descriptions of traffic behavior
in and around the source. The methodology is implemented in quantitative
fashion for the fourth of seven types of complex source, municipal parking
facilities; the information generated, relating parking facility parameters
to the associated traffic behavior, will now be used by the sponsor to
generate guidance for studying the impact of new parking facilities on
air quality,,
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CONTENTS
Page
Abstract Hi
List of Figures v
List of Tables vi
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Characteristics of Parking Facilities 7
V Parking Facility Parameters 15
VI Traffic Parameters, Values and Derivations 30
VII Analysis 35
VIII Results 38
IX Data Sources 51
IV
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FIGURES
No. Page
1 Typical Sloping Floor Garage Designs 12
2 Typical Ramp Garage Designs 12
3 Ninety Degree Double-Stall Attendant-Parking Uses about 170 15
Square Feet Per Car.
4 The 45-Degree Interlock Layout Allows Driver to Return Via the 20
Adjacent Aisle if all Stalls are Occupied in an Aisle.
5 Reservoir Space 23
6 Storage Rate 23
7 Variation in Parking Garage Use 26
8 Accumulation of Parked Cars for a Large Customer-Parking 26
Garage Averaged Over Three Months
9 Mid-Week-Day's Movements in a Typical Parking Garage 27
10 Garage in Threatre Area near Business District 27
11 Late Opening and Closing Stores 28
12 Generalized Methodology 39
13 Generalized Methodology Applied to Parking Facilities 40
14 Isopleths (m sec'l) of Mean Autumn Wind Speed Averaged Through 45
the Afternoon Mixing Layer
15 Isopleths (m sec"^) of Mean Winter Wind Speed Averaged Through 46
the Afternoon Mixing Layer
16 Isopleths (m x 10^) of Mean Autumn Afternoon Mixing Heights 47
17 Isopleths (m x 102) of Mean Winter Afternoon Mixing Heights 48
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TABLES
No. . Page
1 Suggested Unit Parking Dimensions 13
2 Area Per Car in Lots Employing Customer-Parking 18
3 Area Per Car in Lots Employing Attendant-Parking 18
4 Vehicle Exhaust Emissions at Idle in Grams Per Minute 31
5 Base Running Times by Operating Mode at two Example Parking 33
Garages
6 Total (Vehicles Entering Plus Vehicles Exiting) Use Rates 37
for Two Sizes of Parking Garage for Differing Conditions
7 Key to Stability Categories (after Turner 1970) 43
vi
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SECTION I
CONCLUSIONS
1. A general methodology has previously been developed which permits
relating parameters descriptive of traffic behavior associated with
developments (complex sources) to the available descriptive characteristics
of the complexes themselves. These relationships are subsequently to be
used by the sponsor to develop guidance for relating the complex's
characteristics to air quality.
2. The methodology has been successfully applied to the fourth (parking
facilities) of seven types of complexes, with quantitative results presented
in this task report.
3. It is now appropriate to proceed to the next type of complex, and
apply the methodology appropriately.
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SECTION II
RECOMMENDATIONS
It is recommended that, as planned, the project officer employ this
methodology to develop guidance for relating the traffic characteristics
of parking facilities to typical and peak air pollution concentrations.
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SECTION III
INTRODUCTION
INTRODUCTION
OBJECTIVE AND SCOPE
The ability.to estimate traffic characteristics for proposed developments
and the resulting effects on air quality is an important prerequisite for
promulgating State Implementation Plans which adequately address themselves
to the maintenance of NAAQS. Prior to estimating the impact of a develop-
ment (complex source) on air quality, it is necessary that traffic charac-
teristics associated with, the source be identified and related to parameters
of the development which can be readily identified by the developer a priori.
The purpose of this study is to identify traffic characteristics associated
with specified varieties of complex sources and to relate these character-
istics to readily identifiable parameters of the complexes. The end
product of this task will then be used to develop an Air Pollution Technical
Document which will provide guidance to enable control agencies to relate
readily identifiable characteristics of complex sources to air quality.
The work is being performed in seven sub-tasks. Each sub-task is devoted
to examining vehicle behavior and its relationship to readily obtainable
parameters associated with a different variety of complex source. The
seven categories of complex sources are:
1. Shopping centers (Report No. EF-263)
. 2. Sports complexes (stadiums) (Report No. EF-265)
3. Amusement parks
4. Major highways
5. Recreational areas (e.g., State and National Parks)
6. Parking lots (e.g., Municipal) (the present report No. EF-266)
7. Airports (Report No. EF-264)
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This, the fourth task report, describes the methodology developed, and
the analysis and results of its application to parking facilities.
APPROACH
Due to internal constraints, the sponsor has been forced to impose a tight
schedule on this project, permitting only two to three weeks for the analysis
and reporting of each sub-task. Accordingly, the employment of readily
available traffic design information for each type of complex has been
suggested as the general approach.
The approach was designed to permit the development of answers to the
following questions posed by the sponsor, using available traffic design
and behavior data, and available data on parameters of the complex:
1. How much area is allotted or occupied by a single motor vehicle?
2. How much or what percentage of the land occupied by the complex source
(and the source's parking facilities) can potentially be occupied by vehicles?
What is the usual percentage?
3. What portion of the vehicles within the complex are likely to be
running at any given time during a 1-hour period? During an 8-hour period?
We are interested in both peak and typical circumstances here.
4. What is the typical and worst case (slowest) vehicle speed over
1-hour and 8-hour periods?
5. How are moving and parked vehicles distributed within the complex
property? (e.g., uniformly?)
6. What are the design parameters for each type of complex which are
likely to be known by the prospective developer beforehand?
7. Which ones of the design parameters in number 6 can be most successfully
related to traffic and emissions generated by the complex? What is,the
best estimate for relationships between readily obtainable parameters and
emissions?
8. What are the relationships of parking "lot" design to parking densities
and vehicle circulation? What represents a typical design a,nd/or a design
which has highest parking densities, lowest vehicle speeds, longest vehicle
operating times?
9. What meteorological conditions (i.e., atmospheric dilutive capacity)
are likely to occur during periods of peak use? What use level is likely to
occur during periods of worst meteorology (i.e., atmospheric dilutiv*
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The technical approach developed and implemented in this report consists
of, first, structuring a methodology for describing engine operating modes
which considers both the principal modes in automobil.e operation in and
around complexes, and the emission significance of each mode. In our analysis
this leads to an important emphasis on engine operating time, with only
secondary significance attached to operating speed and distance.
For the complex being studied, an analysis is made of the typical movements
of vehicles, and their movements under conditions of congestion, caused by
peak traffic loads or by awkward design elements of the complex, or both.
This highlights the traffic operational modes which have greatest effect
on running times, and assists in seeking out the elements or parameters
of the complex which influence these running times most.
The running times in critical modes are usually found to be dependent on
the usage rate of the complex as a percent of capacity. In addition,
absolute values of usage as a function of time are needed as a direct input
for estimating emissions. Therefore, data on usage patterns of the complex
by season, day of the week, and hour of the day are collected and related
to capacity parameters. The results are used in two important ways:
1. To develop quantitative relationships between running times and various
percent-usage parameters; and
2. To provide general usage patterns from which the usage pattern for
a complex of interest can be inferred, if no measured data are available.
Basic parametric values are then derived which define typical base line
running times and use rates; these are used both to provide a point of
departure for the peak case calculations, and as input to the estimate of
typical conditions.
For any parameter of capacity (e.g., entrance, exit), resulting increases
in running time for each mode are estimated as they may be functions of
the exceedance of that capacity. The base running time is then used in
conjunction with typical use rates to generate typical combinations of
running times and numbers of vehicles running. Finally, peak (1-hour and
8-hour) use rates are compared to capacities in order to calculate, using
the above derived functionalities, the associated peak values of number of
vehicles running, and running times.
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It may often be possible, in addition, to develop and provide qualitative
guidelines which can provide further insight into factors which may aggravate
or alleviate congestion. These are provided separately from the quantitative
relationships.
Finally, the meteorological conditions associated with the occurrence of
the peak "(vehicle number) (running time)" values are defined; in addition
periods of the most adverse meteorological conditions are determined, and
the use rate data examined to determine associated use rates and running
times.
The methodology is considered to be completely general, and to apply to
all the complex sources of concern here, with the possible exception of
the "major highway" case cited in the section titled Objective and Scope.
That special case is recognized in the work statement as a potentially
unusual one, requiring different treatment in the context of the other
six sources.
The remainder of the report describes the implementation of this methodology
for parking facilities, and the results obtained.
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SECTION IV
CHARACTERISTICS OF PARKING FACILITIES
Literature on parking facilities is extensive, and covers such varied and
inclusive areas as trip generation, facility type selection and design,
operational considerations, and functional data. Section IX lists some
of the voluminous literature on the subject, emphasizing those studies
which were most directly applicable to this subtask.
In general terms, parking facilities are classified by size (number of
parking spaces), lots (flat) or buildings (garages), location (core or
fringe), and whether self-parking or attendant-operated.
It will not be our intent here to cover all facets of all parking facility
types, but rather to give a broad picture of most types, and focus on
the more significant ones for detailed analyses. While our eventual focus
will be on attendant-operated multi-story parking garages, the principles of
analysis will be readily seen to be applicable to study of any type of
lot; where important differences exist, they are pointed out.
The material which follows is generally extracted and/or adapted from the
principal parking documents listed in Section IX on Data Sources, and is
intended to set a background stage for the parameter derivation and analysis
which follows.
All cities are expanding their downtown parking supply to meet rising off-
street parking demands. Even the central business districts of older cities
attract an increasing number of visitors by car and are acquiring additional
off-street parking.
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Downtown's off-street parking demands have increased more rapidly than
its daytime population, and reflect the increasing auto-orientation of
both urban residents and downtown land uses. Parking indices - required
spaces per thousand feet of gross floor area - average five for banks and
bus depots; four for libraries, governmental buildings, and grocery stores;
three for department stores; nearly two for offices; and less than one for
furniture stores and hotels.
Supply and use of downtown parking spaces and characteristics of downtown
parkers vary with city size - the more populous the city the higher the
percentage of total spaces in garages. In larger cities, a higher proportion
of downtown trips are made to or from work; consequently, average durations
and walking distances are longer and parking turnover is less. The maximum
accumulation of parkers occurs about noon in all cities.
Parking spaces needs depend on downtown's daytime population, the proportion
of CBD (Central Business District) trips made by automobile for work and
non-work purposes, and public parking policies. Comparisons between parking
space supply and "realized" demand (i.e. the number of parkers actually
accommodated in the area) show a slight space surplus when the entire central
business district is considered. Core areas of most CBD's, however, usually
have a deficiency.
Because more downtown travelers will come from auto-oriented suburban areas
in future years, downtown parking space demands and space needs will continue
to rise in all cities.
Downtown parking space demands car be estimated from a "parking space factor"
applied to central business district person trip destinations by auto.
for an urbanized population of 100,000, approximately 0.16 spaces are
desirable for each CBD destination by auto; when urban population reaches
one million, 0.26 spaces are desirable for each destination.
Values associated with convenient access and parking for workers, shoppers,
and other components of downtown's daytime population are increasingly
recognized. Downtown parking has become a vital community concern - an
integral part of the urban transport system.
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Cities, therefore, nave expanded their downtown space supply in recent
years through various combinations of public and private approaches although
the vast bulk of all off-street parking in the United States has been
developed by private enterprise.
Today, many parking facilities are being constructed to serve department
stores, office buildings, and financial institutions. Even in cities with
existing or proposed rapid transit, the number of downtown department stores
for which convenient parking has been provided is continuing to rise.
The development of off-street parking facilities near outlying radia free-
way interchanges and rapid transit or commuter railroad stations in larger
urban areas will help afford maximum convenience to users and achieve more
efficient use of trunk-line highway and transit routes. Such facilities
are particularly desirable in urban regions of more than two million popu-
lation, where they may equal about one third of the downtown parking supply.
Their success requires fast and frequent express transit or highway service,
short distance between parking lots and transit stops, easy access to and
from major traffic arteries, ample parking capacity for downtown-oriented
travelers, and reasonable parking costs. They often could be coordinated
with commercial and civic developments at major interchange points.
Parking space requirements for the nation's city centers can be predicted
with reasonable accuracy, once the important factors influencing parking
demands are identified and assessed. These factors relate closely to city
size, downtown intensity and land use, and vehicle ownership. Parking
characteristics, patterns, and demands are surprisingly similar among cities
in the same population groupings.
This consistent behavior of parkers suggests a systematic approach to the
dimensioning of downtown's parking needs. The existing parking space
supply provides the logical point of departure. In turn, parking char-
acteristics and habits reflect the socio-economic aspects of downtown
parkers, and provide bases for evaluating locations and usage of proposed
facilities. Finally, supply-demand comparisons serve to measure parking
space deficiencies and needs.
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Such information is an outgrowth of downtown parking surveys conducted in
many of the nation's cities. These surveys are essential for the intelligent
planning of off-street facilities, and include inventories of existing curb,
lot, and garage spaces. Motorists are interviewed to obtain information
on length of stay, distances walked, trip purposes, average fee paid,
orgin of trip, place of parking, and downtown destination. The block-by-
block assessment of demands and deficiencies is a straight-forward process,
once the survey is completed.
Business trips account for one third of all downtown parkers regardless
of city size. In small communities, about one third of all parkers are
shoppers as compared with about one tenth in large cities. In the largest
urban areas, all-day employee-parkers comprise about 40 per cent of the
total and consume about 70 per cent; of available "space-hours."
Accompanying this increase in downtown work trips is a decrease in parking
turnover (parkers per space per day), a lengthening of average parking
duration, and a rise in average walking distances. With outlying shopping
areas developing as cities expand, most convenience goods may be purchased
close to home. Therefore, more downtown shoppers seek specialized com-
modities, make less frequent shopping trips, and stay longer.
This is an appropriate point to introduce a fundamental concept in this
analysis of parking facilities, which differentiates this complex source
from the others being studied (shopping centers, airports, sports arenas,
etc.). In those other cases it is possible to define the automotive trips
which are generated by the existence of the source itself. In the case
of parking facilities per se, the trips are generated by the existence of
other trip generation sources in the area (businesses, stores, and entertain-
ment), and any given parking facility provides only a service function along
with other similar facilities. As a matter of fact, the subject of trip
generation as it relates to the complex of activities which comprise an
urban area represents a principal area of study in the field of urban
transportation, and is far too large and complex a topic to be condensed
here. For parking facilities, the key parameters will be shown to be
parking capacity and use rate.
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Parking garages may be classified by their general type - above ground,
underground, or integral - or by their means of interfloor travel - ramp
or elevator-mechanical. Ramp garages permit either self-parking or
attendant operation, while mechanical garages require attendants.
Underground Facilities - Underground parking garages are normally developed
on sites where property is publicly owned, land is very expensive, and/or
certain esthetic values must be preserved. Although ventilation, illumination,
and utility relocation costs are high, these facilities are usually developed
with little or no land costs, since the surface can be retained for other
uses. Where high-rise buildings are located on garage sites, development
costs closely conform with those for above-ground multideck structures.
Mechanical Garages - These garages utilize some form of electric or
hydraulic elevators and machinery to position cars in stalls. They permit
construction of a greater number of levels and adapt to small and irregular
properties. An often critical disadvantage, however, is their inability
to accommodate heavy peak-hour incoming or outgoing movements.
Ramp Garages - Ramp garages provide either (1) parallel floors with ramp
connections at one or more locations, or (2) sloping floors which permit
parking on both ramp surfaces and builiding floors (see Figure 1 and 2).
Sloping floor garages have\continuous grades, and cars are driven in an
elongated spiral pattern to\ipper floors and brought down by the same
system of aisles. Some designs feature spiral ramps which facilitate
rapid descent from upper floors\ Facilities may incorporate one or more
levels of underground or basementNnarking, and take advantage of topography
to provide multilevel entrances or e^its.
Design Standards
The size, dimension, and over-all weight bYmodern automobiles and trucks
have been key factors in determining off-streot parking standards. Through-
out the United States, building codes are constantly being revised to
accommodate necessary live loads required in final designs for both multi-
deck and roof level parking garages.
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-I.
31
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Figure 1. TYPICAL SLOPING FLOOR GARAGE DESIGNS
(1) Conventional Single Sloping Floor; (2) Single Sloping Floor with Express
Exit Ramp; and (3) Double Sloping Floor.
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Figure 2. TYPICAL RAMP GARAGE DESIGNS
(1) Straight Ramp; (2) Spiral Ramps; (3) Directional Ramps with Retail
area; and (4) Straight Ramps with Retail Area.
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Modern design standards for self-parking garages pertaining to access
points, unit parking dimensions, column spacings, floor heights, and ramp
grades are briefly summarized herein. Only general criteria are presented,
for the detailed design of parking garages is a complex study in itself.
Attendent-served garages differ slightly in some characteristics, e.g.,
stall spacings.
Entrance and Exit Lanes - Access points between garages and surrounding
streets should avoid back-ups and congestion. At least one outbound lane
usually should be provided for each 300 spaces and one inbound lane for
every 500 spaces. Lanes should be 12 feet wide except at points of ticket
issuance or cashier collection, where they should taper to about 10 feet.
Unit Parking Dimensions - The parking unit (including two parking stalls
and an aisle) varies with the "parking angle." Although angle parking is
sometimes more readily acceptable to many shoppers and business-trip
parkers, greater space economy is usually achieved from 90-degree parking.
Suggested unit parking dimensions for 45, 60, and 90-degree parking are
given in Table 1.
Minimum stall widths should be 8.5 feet for angle parking, 9 feet for
90-degree parking, and approximately 10 feet for parallel parking. The
length of a stall (measured on an axis parallel with the vehicle after
it is parked) should be 18 feet. For parallel parking, this length should
range from 22 to 24 feet.
Table 1. SUGGESTED UNIT PARKING DIMENSIONS
ANGLE OF PARKING
45°
60°
90°
DIRECTION OF AISLES
One-Way
One-Way
Two-Way
UNIT PARKING
DIMENSION
48 to 53 feet
57 to 60 feet
62 to 65 feet
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Column Spacing and Clear-Span Construction - Traditionally, columns have
been spaced at intervals of three parking spaces. This results in a 28.5-
foot spacing, assuming 90-degree parking and 18-inch-columns. Because
columns are located three feet in from aisles, a parking unit of 62 feet
requires an over-all minimum column spacing of 31 by 28.5 feet. For larger
columns, this spacing should be increased accordingly to maintain adequate
clearances.
The "column-free" or "clear-span concept" has been widely used to provide
spans up to approximately 65 feet for 90-degree parking. Various theories
and revisions in materials, design concepts, and building methods have aided
in making this concept a reality. These include "ultimate strength" design,
pre-stressed concrete, post-tensioned construction, and new steel and concrete
products with greater tensile and compressive strengths which permit longer
spans with less deflection.
Floor Heights - Floor-to-floor heights usually depend on construction
methods. A minimum clear height of approximately 7.5 feet will normally
dictate a 9.5 to 10-foot floor-to-floor height.
Ramp Grades - A maximum grade of five per cent should be used for sloped
portions of sloping floor garages where ramps provide direct access to
stalls. Where conventional interfloor ramps are used (either straight or
helical), grades should not exceed 10 to 13 per cent; grades of seven to
eight per cent are preferable. Parking should not be permitted directly
off conventional interfloor ramps.
Lighting Intensity - Garage illumination should approximate three to five
foot-candles in parking areas, and 30 foot-candles in cashiering and waiting
areas.
A general comment on parking facility design stems from an overall appreciation
of a wide variety of comments made in the literature on design and operation:
good design and good operating procedures, which are aimed at effective,
economical and profitable operation of a facility, all contribute to the
type of operation which minimizes running time of automobiles in the facility,
and hence pollutant emissions.
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SECTION V
PARKING FACILITY PARAMETERS
The basic parameters which concern us here are the type and size (number
of spaces) of the facility, its physical characteristics, parking facility
use rates, and their variation with season, day of the week and hour of
the day.
Parking facility developers have a large amount of general information
available on parking demand, parking facility design, and use rate charac-
teristics as functions of the type of district (business, shopping, enter-
tainment). In addition, the literature strongly indicates that almost
all urban areas of reasonable size have been subjected to individual studies
in some detail, so that the key parameters and data which are treated in
this section and in the later Analysis Section should be available to, or
derivable by, the developer.
Some parking lots permit self-parking, others have attendant-parking.
Attendant-parking is used at most commercially operated lots because it
permits more efficient use of space. A commonly used plan of attendant-
parking is shown in Figure 3.
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Figure 3. NINETY DEGREE DOUBLE-STALL ATTENDANT-
PARKING USES ABOUT 170 SQUARE FEET PER CAR. IT
IS OFTEN THE ONLY FEASIBLE PARKING PLAN WHERE
LAND COST IS HIGH.
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A self-parking lot offers a minimum of inconvenience and a maximum of
ease. Although the following principles of parking lot design and
operation pertain largely to self- or customer-parking, they apply
also to the development of attendant-parking lots.
Parking lot sizes, measured in terms of cars accommodated, generally
range from twenty-five to five hundred or more. Lots that accommodate
from one hundred to two hundred cars are efficient and practical. A few
small lots, strategically sited, will usually serve better than a single
large one.
Parking lots of large capacity can cause congestion on bordering streets,
especially during peak-traffic hours. If capacity is small and the number
of lots large, the potential traffic congestion tends to spread over several
areas and thus minimize its effect.
If attendant-operated, moderately-sized lots develop better operational
efficiency than large ones. Parking and unparking of cars is accomplished
much more rapidly in lots of low capacity. The distance traveled by attendants
is shorter, service is faster.
For efficient land use, the self-parking lot should provide three hundred
square feet for each car space. Depending on design features, three hundred
square feet is an acceptable standard for quickly estimating capacity for
possible development of a convenient parking facility. A smaller per-car
space area will necessitate narrower stalls and aisles. A higher figure
will allow wider stalls and aisles, more maneuvering space, greater safety
and convenience, and simpler, faster operation.
To minimize conflicts with street traffic, parking lot exits and entrances
should be well-defined and as few in number as practicable to provide for
peak-hour operation. They should be at least fifty feet from intersections.
When the lot fronts on a heavy-traffic street, separate entrances and
exits are best.
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Where possible, parking lot openings should be oriented to favor right-
hand turns for entering and exiting traffic. Where such design is not
possible and there is.considerable street traffic, it may be necessary to
prohibit left turns into and out of the parking lot.
Reservoir space at entrances and exits is of particular importance in
lots on busy traffic streets. Space to accommodate accumulation of incoming
cars prevents back-ups into traffic lanes if claim-ticket issuance delay,
a confused driver, or other conditions temporarily block entering lanes.
Area within the parking lot to accommodate some cars at the exit permits
groups of leaving cars to take advantage of gaps in traffic.
Single-lane entrances to parking lots should be at least fourteen feet
wide. Exits should be a minimum of ten feet. A combined entrance-exit
should be not less than twenty-six feet wide. A1 should have suitable
curb returns.
The minimum area required to park a car is one hundred and forty-four
square feet-a rectangle, eighteen feet long, and eight feet wide. These
dimensions are minimum size for self-parking lots. Stalls eight and one-
half feet wide are preferable. Most shopping centers use nine-foot widths
as a concession to woman shopper and driver. No reduction in the eight-
foot stall is recommended because of the trend towarder wider frames and
doors.
Comparison of per-car area required in lots using self-parking, and those
using attendant-parking shows that driver-parking requires almost twenty-
five percent more space. Tables 2 and 3 give this comparison for a number
of lots. Table 2 shows the area per car for eleven parking lots that
use driver-parking. Area requirements vary from a maximum of three hundred
and seven to a minimum of one hundred and ninety-six square feet, with
an average of two hundred and forty-three square feet.
Table 3 shows similar information for twenty-four lots employing attendants.
The per-car areas vary from two hundred and fifty-one to one hundred and
twenty-seven square feet, averaging two hundred square feet per car.
\ -17-
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Table 2. AREA PER CAR IN LOTS EMPLOYING CUSTOMER-PARKING
Parking Area
In Square feet
20,000
30,000
39,360
33,550
32,800
60 ,000
61 ,224
14,644
23,834
27,780
44,160
Table 3.
Parking Area
in Square Feet
24,645
25,725
11,620
16,200
17,925
19,236
33,575
29,335
27,109
15,500
32,640
12,780
15,225
13,800
16,900
25,320
17,289
15,380
12,000
9,900
10,150
19,792
8,180
7,656
Number of Cars
65
100
137
121
128
251
260
65
no
130
225
Average
AREA PER CAR IN LOTS EMPLOYING
Number of Cars
98
110
50
70
78
85
147
133
128
75
163
65
78
73
85
135
95
86
70
58
60
118
55
60
Average
Area per Car
1n Square Feet
307
300
.283
277
256
239
235
225
216
213
196
243 square feet
ATTENDANT-PARKING
Area per Car
in Square Feet
251
234 .
232
231
229
226
221
220
211
206
200
196
195
189
187
187
182
178
171
170
169
167
148
127
200 square feet
-IB-
-------
Varying the angle of parking changes the length of curb and width of aisle
required for each car. The parking angle determines the efficiency of
lot design because it governs the car space area.
Normally the most efficient use of space is obtained when parking stalls
are laid out perpendicular to the aisles. This plan provides more stalls
per unit area and permits parking and unparking in either direction. Angled
parking yields, fewer stalls for a given length of parking curb and permits
parking and unparking in one direction only. However, angle parking is
more convenient. Drivers find it easier to maneuver in and out of angled
stalls; also it is easier to spot empty spaces.
Back-in parking requires narrower aisles than drive-in, but backing in
requires more maneuvering ability than drive-in angle parking and takes
more time. Most designers are reluctant to use back-in parking in customer-
parking facilities because its difficulty may neutralize the driver-convenience
that so often motivates parking lot development.
For space-saving, however, back-in parking is often used in lots with parking
attendants. Twenty of the twenty-four attendant-operated lots reported
in Table 3 use back-in parking. The average area per car of these twenty
lots is one hundred and ninety-seven square feet. The average area of
the remaining four lots that employ head-in attendant-parking, is two
hundred and twenty-four square feet per car.
Lots with angled stalls require continuous aisles because unparking cars
are always headed in their original direction. The best aisle-plan for
such is a series of continuous one-way aisles that alternate in direction.
This requires that the angled stalls be laid out in an interlocked rather
than herringbone pattern. See Figure 4. One-way aisles are desirable
because they are most economical of space and eliminate head-on and side-
swipe accidents.
When ninety-degree parking is used, cars can unpark to the right or left
and may use the aisle in either direction. Two-way aisles reduced travel
distance-parking and unparking cars can take the most direct route to
their destinations. Some lots may necessitate a few dead-end aisles to use
all available area. In those cases, ninety-degree parking must be used.
-19-
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Figure 4. THE 45-DEGREE INTERLOCK LAYOUT ALLOWS DRIVER
TO RETURN VIA THE ADJACENT AISLE IF ALL STALLS ARE OCCUPIED
IN AN AISLE. STALL-BUMPER LAYOUT IS FAIRLY SIMPLE; EVEN
IF THE BUMPERS ARE NOT ESPECIALLY EFFECTIVE, THERE IS LITTLE
CHANCE FOR COLLISION DAMAGES.
-20-
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Circulation aisles within the parking lot should be laid out to reduce
travel distance and the number of turns. A poorly designed system of
aisles, requiring excessive travel and turning for drivers to find an
empty stall, develops confusion and hazard. Directional signs, prominently
displayed, can help create orderly and safe inter-lot circulation.
Parking lot aisles should be as wide as practical. Wide aisles permit
the entering driver to spot empty stalls quickly and encourage quick,
easy parking. The faster an entering car is parked, the less it contributes
to congestion.
Parking facility characteristics are given in the following summary material:
Facility Size
Minimum Capacity
Maximum Capacity
.Maximum Number of Levels
Entrances and Exits
Number
Width of Lanes
Reservoir Space
Inbound
. Capacity
Lane Width
Number .of Lanes
Outbound
Lane Width
Number of Lanes
' i. ..'.
Celling Height
Main Floor .
Storage Floors
Ramps
Slope
Width
' Straight Ramps
.Curved Ramps, inside lane
Curved Ramps, outside lane
Curvature
200 cars
500 cars
500 cars
1, with multiple lanes. As far from
street intersections as possible,
oriented to favor right turns.
12 feet
Fraction of average peak
inbound flow as determined from
Figures 5 and 6
12 feet
4
12 feet
at least 2
12 feet
7 feet, 6 inches
15 per cent maximum
11 feet
12 feet
10 feet, 6 inches
32 foot diameter to inside lane edge
-21-
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Parking Stalls
Type
Attendant-parking back-in
Self-parking . drive-in
Angle of Parking 90 degrees
Length 18 feet
Width
Attendant-parking 8 feet
Self-parking 6 feet, 6 inches
Access Aisles
Width
Attendant-parking 22 feet
Self-parking 24 feet
Curbs
Height 6 inches, maximum
Width 18 inches, mimimum
The average time required for an attendant to park one car and return to
reservoir area for another is the rate of storage or rate of parking.
It can be computed from the formula,
p = 60N
as shown in Figure 6. P is the parking rate in cars an hour. N is the
number of attendants. And T is the average time in minutes required by
an attendant to park a car and return to the reservoir area for another.
The best physical arrangement of reservoir space is in the form of lanes
leading from the entrance to the ramp. As cars come into the garage,
they are directed into successive lanes. Drivers are asked to drive into
the garage as far as possible, thus filling the reservoir area one lane
at a time. After cars are ticketed, they are moved out of the reservoir
area to storage floors in order of arrival, one lane at a time, where several
lanes are used.
Appearance of the reservoir area in an attendant-operated garage is important.
It, the cashier's booth, and the waiting room are the only parts of the
garage that customers see. The reservoir lanes should be kept well-cleaned
and properly lighted. They should also provide adequate space for safe
pedestrian movement.
-22-
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STORAGE RATE 1.10 ARRIVAL RATE
0 20 40 CO 80 100 120 HO 160 180 200 220 240
AVERAGE NUMBER or CARS ARRIVING DURING PEAK HOUR
Figure 5. RESERVOIR SPACE
0 20 40 60 80 100 120 140 160 180 200 220 240
AVERAGE NUMBER OF CARS ARRIVING DURING PEAK HOUR
Figure 6. STORAGE RATE
-23-
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Width of reservoir lanes should be enough to permit customers to get out .
of their cars comfortably and without danger from moving cars in the adjacent
lane. Twelve-foot lanes are recommended. White-painted walkways will
serve the dual purpose of directing pedestrians along the safest path and
adding to the well-kept appearance.
Layout
Layout sketches comparable to those in Figures 1 and 2 are useful in helping
define the running times required for Section VI on Traffic Parameters.
Trip Generation
As indicated in the preceding section, the concept of trip generation is
relevant to the activities (business, shopping, entertainment) in the area
served by the parking facility of interest (along with others in the area),
and not to the facility itself.
Trip generation thus governs the overall flow of traffic into and out of
parking facilities, uut the specific use rates are as strongly governed
by the parking capacity (number of spaces) of the individual facility.
It is important to note that, while parking facilities associated with other
complex sources (shopping centers, e.g.) may encounter demands which exceed
their capacity, a parking facility per se, subject to any degree of control,
will almost never be subject to a capacity exceedance. In fact, it will
rarely reach capacity. In other words, whether self-parking or attendant
parking is involved, when there is any degree of control attempts to enter
will be turned away (as by "sorry-full" signs) whenever occupancy approaches
capacity. Thus, where other complexes are responsive to some extent to
trip generation concepts, a parking facility's parking capacity is the
principal determinant as regards its use rate.
Note that the absolute magnitude of trip generation does play a part, but
that it operates on a higher level of consideration - city planners are
concerned with trip generation for a broader metropolitan area, consisting
of a variety of use purposes (work, shopping, entertainment) and severed
by a number of types and sizes of parking facility. Thus, given that a
.determination is made that general trip generation studies by city planners
-24-
-------
show sufficient requirements to suggest that need for a parking facility,
the techniques of this report can be used to study that facility's traffic
characteristics, and fluctuations in overall trip generation will cause
corresponding fluctuation in use rate of a given facility.
Spaces and Use Rates
Characteristic space data has been given earlier in this section. Here
we will show some general data on typical hourly, daily and seasonal
use rates, and some more specific, but still characteristic, data on
diurnal variations in use rates.
These data are representative examples of information obtained through
analysis of parking garages - on the rate of inbound and outbound
movements, peak hours, and variations in use rates by hour, day and month.
The peak use occurs during the Christmas shopping period. The remainder
of the annual cycle ranges from the low point during mid-winter (usually
February) to a secondary peak in late spring (usually April). Variation
by month and season is illustrated in Figure 7a.
The cycle by days of the week is seen in Figure 7b, and for an average
business-oriented day (little or no evening activity), the hourly variation
in use is represented in Figure 7c.
Figures 8, y, 10, and 11 present data on entrance and exit rates as a
function of time of day for, respectively: Figure 8 the overall average
weekly pattern by hour of the day; Figure 9 an average midweek day with
little or no evening activity; Figure 10 a combination of the usual
daytime pattern of workers, visitors and shoppers, with theater traffic
in the evening; Figure 7 the usual daytime pattern, with evening shopping.
Example data for times spent in various steps in parking and unparking
in an attendant-parking facility are as follows (actions marked with an
asterisk are relevant to running times):
-25-
-------
MONTHS OF THE YEAR
DAYS OF THE YEAR
HOURS OF THE BUSINESS DAY
w
I*.
c
H
i>
W
u
u
e-
12
11
10
9
8
6
5
4
2
1
0
MONTHLYr,; 13 m AVI RAC.I M H R
irzz-^r ,{i^: *tr^r^V^:^';
3 N^333^1
IBIlllilff
tftillifiilt
llllplllfilf
i
a.
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22
20
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h
Q 12
u.
O ,/>
UJ O
u °
u
w
su 6
f> '.! i
GO o c ci c* v. v
r^ooTTTc'i-^.weo
o o
c.
Figure 7. VARIATION IN PARKING GARAGE USE
CARACF. CAPACITY = 136 CARS-.
700
6
Fi
gure 8. ACCUMULATION OF PARKED CARS FOR A LARGE CUSTOMER-PARKING
GARAGE AVERAGED OVER THREE MONTHS.
-26-
-------
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J
a
7.
0 nn
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u 10 S
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Figure 9. MID-WEEK-DAY
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TIME
'S MOVEMENTS IN A TYPICAL PARKING GARAGE
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NOON 12J4567891011
TIME
Figure 10. GARAGE IN THREATRE AREA NEAR BUSINESS DISTRICT.
-27-
-------
100-
-CAFACITY=>94 CARS.
-500
8 9 10 II NOON 1
8 .9 10 11 13
TIMS
Figure 11. LATE OPENING AND CLOSING STORES
PARKING
Attendant accepts car, gets in and starts it*
Drives on main floor to ramp*
Drives on ramps (average of 2 levels at 12 seconds a level)*
Average delay on ramps*
Drives on storage floor*
Maneuvers into parking stall (back-in)*
Stops car and gets out*
Notes location of car on office portion of Identification
ticket
Walks to elevator (plus 6 seconds average wait for elevator)
Rides to main floor in elevator
Walks to Cashier's booth to deliver identification ticket
8 seconds
4 seconds
24 seconds
15 seconds
6 seconds
18 seconds
6 seconds
31 seconds
45 seconds
20 seconds
8 seconds
185 seconds
-28-
-------
UNPARKING
Attendant accepts identification ticket at Cashier's booth
Walks to elevator
Rides to storage floor in elevator
Walks to parking stall
Checks identification of car
Gets in car and starts it*
Unparks and drives on storage floor*
Drives on ramps*
Average delay on ramps*
Drives on main floor*
Stops car in delivery area and gets out*
Accepts customer's ticket and delivers car to him*
The data presented 1n this section are employed subsequently
on Traffic Parameters, on Analysis, and Results.
5 seconds
8 seconds
20 seconds
45 seconds
20 seconds
8 seconds
8 seconds
(
24 seconds
15 seconds
6 seconds
6 seconds
10 seconds
175 seconds
in the sections
-29-
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SECTION VI
TRAFFIC PARAMETERS, VALUES AND DERIVATIONS
CONCEPT OF EMISSIONS PER UNIT TIME
In municipal parking facilities, maximum vehicle speeds rarely exceed 10 mph,
and average speeds are much lower. The usual procedure for estimating motor
vehicle emissi&ns as a function of vehicle speed is not very accurate at
these low speeds due to:
a. Difficulty in estimating average operating speed; and
b. Variation in observed emission rates per unit distance travelled
with slight change in average operating speed.
For parking facilities, analysis shows that traffic operations and their
related emissions are better considered in units of time (grams/minutes)
rather than units of distance (grams/mile), for the following reasons:
1. The variations in emission per unit time at different speeds are
relatively significant at the lowest speeds;* and
2. Traffic movement in a parking facility can be described more accurately
and more easily in terms of minutes of running time, than in terms of
average speed, particularly when engine idling can predominate during
congested periods.
Values for atuomotive pollutant emissions in grams/minute at idle are avail-
able from A Study of Emission from Light Duty Vehicles in Six Cities.10
They are summarized in Table 4. These test data compare well with emission
factors calculated from the current edition of AP-42,12 when converted to
grams/minute at various speeds and then extrapolated to zero speed.
*Less than 50 percent increase from idle to 15 mph.
-30-
-------
Table 4. VEHICLE EXHAUST EMISSIONS AT IDLE IN
GRAMS PER MINUTE*
Pollutant Emissions, gm/min
Carbon monoxide 16.19
Hydrocarbons ' 1.34
Oxides of Nitrogen 0.11
*These values do not include emissions due to the cold start of engines
or to evaporation of gasoline at the end of a trip ("hot soak"). If
subsequent investigation of the relative magnitude of these emissions,
compare to the totals generated by the methodology of this report,
indicates that they are significant, appropriate values for each cold
start and hot soak can be inserted as the total emissions for the start
and stop modes, respectively. Since data for cold start and hot soak
emissions would be reported per occurrence, there is no need to deter-
mine an associated running time or emission period for the modes.
In applying the recommended procedure of emission estimation, total emissions
from the parking facility at any time would be the product of the number
of vehicles, times average vehicle running time, times the appropriate
emission factor from Table 4.
ETotal = (V) (RT) (EF)> where
V = Traffic volume during period of concern
RT = Average running time, minutes
EF = Emission factor, grams/minute.
Operational Modes in Parking Facilities
For purposes of analysis, traffic movement in a parking facility has been
divided into eight characteristic operational modes. These are summarized
below.
Approach (A) - The time or distance along the immediate access road that
total traffic movement is strongly affected by the vehicles entering and
exiting the parking facility. Because, as discussed in Sections IV and V,
trip generation is caused by the urban activities and not the parking
facility, we suggest a small, nominal value for this, of the order of
the average time to traverse a city block.
-31-
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Entrance (I) - Movement through the entranceway, including waiting time
in a entrance queue.
Movement in (MI) - Driving time (or distance) from the entranceway to
the average parking space (third floor in a five-floor garage, e.g.).
Stop (S) - Parking of the vehicle and shutoff of the engine.
Start (St) - Starting of the engine and egress from the parking space.
Movement out (MO) - Driving time or distance from the parking space to
the exitway.
Lxit (E) - Movement through the exitway, including waiting time in a exit
queue.
Departure (D) - The time or distance along the immediate access road that
movement continues to be influenced by traffic from the parking facility.
See the note above on the Approach mode.
The average running time in each of these modes can be quantified for
a specific parking facility as a function of its physical dimensions,
traffic control devices, traffic volume, and type of operation.
Base Running Time
There is an average minimum vehicle running time for each parking facility
that is associated with periods of low or zero traffic congestion. This
concept of a minimum or base running time is important because it usually
is the most common (typical) operating condition at the parking facility,
and because at most facilities it is expected to be exceeded only during
periods of relatively high entrance or exit volumes. The base running time
can usually be determined from a plan of the facility, with additional
knowledge of any traffic control devices, probable driving pattersn, and
operational customs.
liase running times for two example parking facilities have been constructed,
uoth by time measurement during typical driving cycles, and by estimates
based on dimensions of the facilities, entrance/exit configurations, and
expected driving patterns. Total base running times and average times in
each operational mode are shown in Table 5. Certain of the self-parking
times are longer because of idling periods which exist during self-parking,
but not in the attendant case, since the engines are shut off while cars
are stopped.
-32-
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Table 5. BASE RUNNING TIMES BY OPERATING MODE AT
TWO EXAMPLE PARKING GARAGES
Operational Mode
Approach
Entrance
Movement in
Stop
Start
Movement out
Exit
Departure
Total BRT
Base Running Time, Minutes
Attendant-Operated
0.5
0.2
0.8
0.3
0.1
0.9
0.1
0.5
3.4
Self-Parking
0.5
0.3
1.0
0.3
0.1
1.0
0.5
0.5
4.2
Relationship Between Running Time and Traffic Volume
As traffic volume in or out increases, running times may become longer
due to congestion. Some of the constraints to movement that contribute
to the longer running times are:
Queues at entrances and/or exits due to approaching
entrance/exit capacity
* Queues created as vehicles attempt to exit onto uncontrolled
access roads
o Increased time required to find space as parking space
capacity is approached techniques for estimating increases
in running times are discussed in the Analysis section.
Identification of Critical Modes for Parking Facilities
The following discussion is more relevant to self-parking facilities than
to attendant-parking, because of the fact that attendant operation involves
shut-off of engines while standing in the entrance mode, and no idling
at exit for payment.
-33-
-------
Examination of the eight operational modes that were identified indicates
that for parking facilities, running times in some modes are relatively
constant, but that times in others may increase from the base running time
during peak usage conditions. For parking facilities, the three modes
whose times may be most affected by traffic congestion, in order of
decreasing impact, are:
1. Exit
2. Movement to a parking space
3. Entrance
Exit and entrance times are functions of the egress and ingress capacities,
respectively, of the individual parking facility exit/entrance ways. As
these capacities are approached or exceeded, running times in the two
modes increase. Waiting times in the resulting queues become the primary
factors in determining total running times. However, because of diurnal
variations in the number of vehicles entering and leaving shopping centers,
egress and ingress capacities generally are not exceeded simultaneously.
Movement time into a parking space, the remaining critical mode, is a
function of the number of free parking spaces. The time in this mode
increases somewhat with parking facility usage, until the number of
parked cars approaches the capacity of the facilities. Then, in controlled
facilities, no further entrance is permitted.
The parameters developed above are analyzed further with the parking facility
parameters in the Analysis section, and findings employed in the Methodology
section.
-34-
-------
SECTION VII
ANALYSIS
In this section we make the necessary interpretation and inferences for
converting the data of the section titled Parking Facility Parameters
into the relationships needed for input to the methodology of the section
titled Results. In the section titled Traffic Parameters, Values and
Derivations, we identified the entrance/exit capacities, and the parking
capacities, as the parking parameters which could, under conditions of
exceedance, increase either, or both, the vehicle running times and the
number of vehicles running.
We require information on parking capacity, entrance/exit capacities, use
_
rates, and running times. - v *
PARKING SPACE CAPACITY
Parking capacities are fixed input values for any specified facility, and
are given in Section V as ranging from 200 to 500 and up. It is important
to emphasize here that controlled parking facilities almost never let parking
reach capacity, and that of the order of 80%, or possibly on rare occasions
90%, of the capacity is as much as is ever reached.
ENTRANCE/EXIT CAPACITY
Characteristic entrance capacities are derivable by considering the factors
given in Section V for attendant-parking. Characteristic values for lots
in the 500 to 700-space size are in range of 100 to 150 cars per hour.
They may be increased during peak periods by increasing the number of
attendants, as by overlapping shifts, for example. Generally the operation
will be planned to minimize the posibility of any exceedance of entrance/
exit capacity, essentially by adjusting the capacity to meet the demand
rate, or alternatively by adjusting the demand rate (i.e., stopping attempted
entrances for a period) to match the capacity.
-35-
-------
Use rates are exemplified by the data given in Section V. The number
of vehicles running during any given 1 -hour or 8-hour-period is equal to
the sum of the vehicle entrances and vehicle exits during that period.
If the entrance times and exit times approximate each other, then the
total figure may be used; otherwise the "in" mode time must be paired
with the numbering of entering cars, and the "out" mode with the exiting
cars. Example totals from the figures of Section V are given in Table 6.
The peak monthly use rate occurs in December (9% compared to the 8.3%
monthly average use rate) ; the day of the week peak is on Saturday (22%
compared to the 14% average); and the peak one hour period may occur at
various times, depending on the type of neighborhood. Where shopping
governs, the peak usually occurs early on Saturday afternoon. If shopping
and entertainment are combined, then the peak may shift into late afternoon
or early evening. The peak 8-hour period will generally run from around
10:00a.m. to 6:p.m.
ENTRANCE/EXIT CAPACITY EXCEEDANCE
While it has been pointed out that such exceedances will rarely occur
in attendant-parking facilities, they may occur in self-parking facilities.
First, running times in queues at under capacity may be calculated by the
equation given in previous reports in this series:
RT = b(^-) , where
I o
a . utilization factor
b = average service time, min/veh (inverse of gate capacity)
For those periods when flow exceeds capacity, the queue continues to
build during each time increment by the amount that traffic volume
exceeds capacity. Average running time for this (unlikely) situation
can be estimated by a stepwise procedure as given in the first report in
this series, EF-262 on Shopping Centers.
-36-
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Table 6. TOTAL (VEHICLES ENTERING PLUS VEHICLES EXITING) USE RATES
FOR TWO SIZES OF PARKING GARAGE FOR DIFFERING CONDITIONS
Half-Hour
Period
6:00-6:30a.
6:30-7:00a.
i 7:00-7:30a.
7:30-8:00a.
! 8:00-8:30a.
1 8:30-9:GOa.
'9:uO-9:30a.
9:30-10:00a.
10:00-10:30a.
.10:30-11:003.
11:00-11:303.
I1:30-I2:00p.
12:00-12:30p.
12:30-1 :00p.
1:00-1 :30p.
l:30-2:00p.
'2:00-2:30p.
2:30-3:00p.
3:00-3:30p.
3:30-4:00p.
4:00-4:30p.
4:30-5:00p.
5:00-5:30p.
5:30-6:00p.
6:00-6:30p.
6:30-7:00p.
7:00-7:30p.
7:30-8:00p.
8:00-8:30p.
8:30-9:00p.
9:00-9:30p.
9:30-10:00p.
10:00-10:30p.
10:30-11 :00p.
11:00-11 :30p.
11:30-12:003.
Large Size
(approx. 700 spaces)
Average
Weekly Pattern
0
0
2
2
12
9
46
34
78
112
120
118
115
136
141
135
160
140
135
130
154
130
109
102
70
20
6
4
4
0
0
0
0
0
0
0
Midweek
Day
0
o -
0
0
7
13
43
15
70
90
72
73
100
122
95
106
110
110
103
89
122
118
112
78
70
12
7
0
0
0
0
0
0
0
0
0
Medium Size
(approx. 500 spaces)
Business/
Theater
0
2
0
3
8
19'
13
17
20
37
39
38
38
37
52
43
56
66
64
63
73
65
60
70
57
75
55
80
66
90
74
63
27
0
0
0
Evening
Shopping
0
7
4
2
32
23
47
37
31
43
40
40
35
24
25
18 -.
14
29
38
31
28
46
51
44
58
24
25
22
37
43
35
27
26
42
38
0
-------
SECTION VIII
RESULTS
THE METHODOLOGY
In general terms, the methodology proceeds as described in the first para-
graph which follows. We wish to emphasize that this description is of
the technique, shown in schematically in Figure 12, in its most general
form, and as such will provide the starting for each of the complexes to
be studied in subsequent tasks. Differences in implementation are expected
to arise in the case of each complex.
Starting from the physical, geographic, and demographic characteristics
of the complex, we use the concepts of operational traffic modes to generate
best estimates of typical and peak trip generation rates, and of base
running times for cars associated with the complex. We also define the
parameters of the complex which significantly and adversely impact traffic .
behavior. The typical trip rates and base running times provide the data
for typical conditions for the required time periods. Quantitative rela-
tionships are defined or estimated for the controlling parameters of the
complex and of the affected traffic modes, and these in turn are superimposed
on the base running times to generate peak running times. The peak running
times are then associated with peak trip generation rates to create the
peak information for the required time periods. We next see how this
generality becomes more specific for a given type of complex.
In the case of parking facilities, trip generation is not relevant, as
discussed in V and VII; as shown in Figure 13, the methodology proceeds
from basic information about a given parking facility (see the section
titled "Parking Facility Parameters"), via traffic behavior data (see
the section titled "Traffic Parameters, Values and Derivations"), and
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OriaracteristicN,
Parameters V
af Complex J
Trip
Jeneration
Analysis
/"Peak
/ Trip
V Generation,
x^
rExceedance ]
Values )
TypicalN
Trip )
kGeneration I
^Values ^/
Peak
-H Running
Times
Peak Values^X
of Numbers of \
Cars Running, andr*-
Base Running / ;
Time ^/
Base
Running
Time
f Peak Values
of Numbers of
Cars Running, anc}
Peak Running
Times
rpical Values'
of Numbers of
Cars Running, and)
Base Running
Times
Figure 12. GENERALIZED METHODOLOGY
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Characteristics Parameters
of Parking Facility
PhysicalN
Layout \
Operational I
Information/
^/
'Number of N,
Entrance and \
I Exit Gates and I
Gate Capacity /
Number of\
Parking )
Spaces^/
(Demographic)
\Envi ronmeny
Typical and \^
Peak Values of \
Vehicles Enter- I
and Leaving/
fBase
Running
Time
(Gate\
I Exceedance )
/Typical and
' Peak Vehicles
Running, and Base
\Running Times
V^
Figure 13. GENERALIZED METHODOLOGY APPLIED TO PARKING FACILITIES
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typical use rate data (see the section titled "Use Rates"), to generate
estimates of typical numbers of vehicles running and associated running
times for 1-hour and 8-hour periods; these are two of the required end
products of the task. For the peak case, peak use rates are estimated
(see the section titled "Use Rates") and then used to obtain exceedance
estimates for gate capacity the principal controlling parameter (see the
sections titled "Entrance/Exit Capacity and Capacity Exceedance") these
latter generate the associated increases in both numbers of vehicles running,
and vehicle running times. These increases are combined with the base
numbers described above, to provide the other two major products, the
peak running times and vehicle numbers for one-hour and eight-hour periods.
The specifics of the procedure are presented in the following paragraphs.
It is first important to note that the concept of trip generation, which
has been fundamental to the analysis of the other Complex sources in this
series of reports, is not directly relevant in the case of an individual
parking facility, but rather to a demographic area, as discussed in
Sections V and VII. Second, each facility will be unique in its detailed
design, and in its use context, so no rules of thumb are considered feasible/
Accordingly, we define our parking facility in terms of physical layout
(including reservoir* specifications and other such details), plan of
.
operation (number of attendants and schedule, e.g.,), number of entrance
and exit gates and their capacity, number of parking spaces, and the demo-
graphic environment and expected uses (business, shopping, entertainment)
and their distribution in time. By analyses like those exemplified in
Section V and VII, we generate characteristic and peak inflow and outflow
rates. We maintain these separately until we determine whether the typical
and peak running times show significant differences between total movement-
in times and total movement-out times. If they are different, we maintain
the separation; otherwise thay may be combined and used as total running
times. A traffic modal analysis (Section VI and VII) provides base running
times, separable by movement-in and movement-out 1f necessary. If gate
capacities are indicated to be exceeded at peak times, then the gate
exceedance analysis of Section VII is applied to determine the corresponding
increases in running times and numbers of vehicles running.
* Reservoirs (space reserved at entrances and exits for waiting cars) assist
in determining entrance/exit capacities.
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The resulting increases in times are added to the base running time to
give peak running time; the peak use rates will, as for the typical case,
give the base peak number of vehicles running, to which we add any additional
vehicles running because of entrance/exit exceedance.
We thus have the four basic numbers required for each of the two time periods
for input to the emission rate calculations: typical and peak numbers of
vehicles running during one-hour and eight-hour periods, and their associated
typical and peak values of vehicle running times.
GEOGRAPHIC DISTRIBUTION
Running times, and hence emissions, from a parking facility can usually
be considered as being distributed fairly uniformly through the facility
area during typical operating periods (base running times). For most
analyses, an assumption of a geographically uniform emission density is
thus sufficiently accurate.
Peak traffic conditions may result in either the entrance or exit capacities
being exceeded, or both. If gate capacity is exceeded, a substantial part
of the total running time and emissions become concentrated at the entrance/
exit ways.
For parking garages, the proposed construction should be studied for its
ventilation characteristics. Open construction means the emissions should
emerge uniformly around the building edges, but distributed at different
levels, depending on the number of floors. Closed construction should be
examined for the principal emission sites.
METEOROLOGICAL ASPECTS
The meteorological characteristics which most importantly affect atmospheric
dilutive capacity are mixing height, wind speed and atmospheric stability.
A convenient summary of mixing height and wind speed characteristics which
affect air pollution potential is given in the Office of Air Programs
Publication No. AP-101 (Holzworth 1972). Atmospheric stability may be
determined in terms of cloud cover, solar radiation and wind speed by a
method proposed by Pasquill and shown in Table 7. For ground level, and
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Table 7. KEY TO STABILITY CATEGORIES (after Turner 1970)
Surface Wind
Speed (at 10 m),
m sec"1
<2
2-3
3-5
5-6
. >6
Day
Incoming Solar Radiation
Strong
A
A-B
B
C
C
Moderate
A-B
B
B-C
C-D
C
Slight
B
C
C
D
D
Night
Thinly Overcast
or
>_ 4/8 Low Cloud
£
D
D
D
£ 3/8
Cloud
F
E
D
D
The neutral class, D, should be assumed for overcast conditions during
day or night.
NOTE: Class A is the most unstable, class F the most stable class. Night
refers to the period from 1-hour before sunset to 1-hour after sunrise.
Note that the neutral class, D, can be assumed for overcast conditions
during day or night, regardless of wind speed.
"Strong" incoming solar radiation corresponds to a solar altitude greater
than 60° with clear skies; "slight" insolation corresponds to a solar
altitude from 15° to 35° with clear skies. Table 170, Solar Altitude
and Azimuth, in the Smithsonian Meteorological Tables (List 1951) can be
used in determining the solar altitude. Cloudiness will decrease incoming
solar radiation and should be considered along with solar altitude in
determining solar radiation. Incoming radiation that would be strong with
clear skies can be expected ..to be reduced to moderate with broken (5/8 to
7/8 cloud cover) middle clouds and to slight with broken low clouds.
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near ground level, sources, such as automobiles in parking facilities,
the ground level concentrations, both in the vicinity and downwind of
the sources will be inversely proportional to wind speed and mixing height
and directly proportional to atmospheric stability (i.e.,' the more stable
the atmosphere, the higher the concentration).
The season of peak use of park-ing facilities is cited as the shopping
days preceding Christmas, with the highest day usually being the Saturday
before Christmas. The peak hour of use on any given Saturday is generally
3 to 4p.m. The peak 8-hour period is generally 10a.m. to 6p.m. A
Secondary 1-hour peak use period may occur during weekday evening hours
at various times between 7 and 9p.m.
Since the pre-Christmas period occurs during the transition from autumn
to winter, the meteorological conditions which characterize the period
of peak use of shopping centers should be estimated by interpolating
between autumn and winter means. Mean afternoon wind speeds and mixing
heights for autumn and winter, for locations in the contiguous United
States, are shown in Figures 14 through 17, taken from Holzworth, 1972.
For most locations the diurnal variation in mean wind speeds" is small,
and the values shown for afternoon means may also be used for the
secondary evening peak use period. Also, since the transition to a strong
restraining nighttime mixing height has generally not occurred by early
evening hours, the afternoon mixing height can serve as a useful estimate
for the evening peak use period. For the Saturday afternoon peak, atmospheric
stability classes B, C and D may occur with classes C and D being the
most prevalent. During the evening hour peak, classes D and E may occur.
Atmospheric dispersion calculations reported by Turner (1970) for stability
classes D and E show that ground level concentrations from ground level
sources will generally be twice as high for class E as for class D. There-
fore, the secondary evening peak use period, which is associated with
more stable conditions, is the more critical period for air quality consi-
derations from the viewpoint of joint consideration of peak use and adverse
meteorology.
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r*
en
Figure 14. ISOPLETHS (m sec'l) OF MEAN AUTUMN WIND SPEED AVERAGED THROUGH THE AFTERNOON
MIXING LAYER
-------
Figure 15. ISOPLETHS (m sec-1) OF MEAN WINTER MIND SPEED AVERAGED,THROUGH THE AFTERNOON MIXING LAYER
-------
16
Figure 16. ISOPLETHS (m x 102) OF MEAN AUTUMN AFTERNOON MIXING HEIGHTS
-------
10
12
Figure 17. ISOPLETHS (m x 102) OF MEAN WINTER AFTERNOON MIXING HEIGHTS
-------
The period when meteorological conditions are least favorable for diluting
pollutants is the period when parking facilities are essentially not in use.
This would be from very late evening until a few hours after sunrise. It
is most often during this period that mixing heights are lowest, wind speeds
are lowest, and atmospheric stability is greatest. For most parts of the
country, autumn is the season when the least favorable conditions are most
likely to occur.
If one now considers that operating hours for parking-facilities are generally
7a.m. to llp.m., then, from a meteorological point of view, the single
hour least favorable for dispersing pollutants during that period is from
10 to llp.m. during the autumn season. The least favorable 8-hour period
would be from 3 to llp.m. Use levels for parking facilities during these
periods may be derived by appropriate techniques.
QUALITATIVE GUIDELINES
In addition to the quantitative evaluation procedures developed above, the
review of parking facilities as complex emission sources should also include
the following considerations which are not presently reducible to quantita-
tive terms:
1= Main entrance/exit ways whould preferably be on a highly visible local
secondary street that feeds into the nearest arterial, so that the transi-
tion from highway driving to parking lot driving and vice versa are not too
abrupt.
2. Any left turn movement across traffic flow that is used by a signif-
icant number of the parking facility patrons is a potentially large conges-
tion point and emission problem.
3. All available information on logical, effective, profit-oriented and
efficient design for parking facilities indicates that, the better design
is from these points of view, the less likely is the congestion which
causes lengthy running times associated with large numbers of vehicles
running. This is a case where good design improves (lessens) emission
characteristics. Accordingly all design and operating features should be
examined critically to insure that they contribute to smooth flow and
short running times.
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THE NINE QUESTIONS
While the specific information called for by the task work statement
has been provided in the sections from Regional Shopping Centers Parameters
through Meteorological Aspects, the nine questions spelled out as part of
the work statement warrant specific response to demonstrate that they are
treated.This is given here, with the questions abbreviated.
1. Area allotted to or occupied by a single vehicle? The area varies
widely - see Sections IV and V.
2. Percentage of land and parking spaces potentially occupied by vehicles?
The usual percentage? See Sections IV and V.
3. Typical and peak values (absolute or fractional) of vehicles running
for 1- and 8-hour periods? This question is treated in Sections IV, V
and VII.
4. Typical and worst case (slowest) vehicle speeds? In the context of
our approach, this question is only relevant to analysis of the "Major
Highway" complex source task. It will be dealt with in that task report.
5. Vehicle distribution within the complex? See section titled Geographic
Distribution. , :
6. Design parameters of the complex likely to be known before hand?
See section titled Parking Facility Parameters.
7. Design parameters in question (6) which can be most successfully
related to traffic, and hence emissions? See section titled Analysis.
8. Relationships of parking lot design to parking densities and vehicle
circulation? What is typical design? Design with highest parking densities,
lowest vehicle speeds, longest vehicle operating times? To the extent
to which these questions are relevant to our methodology, they are answered
in the section titled Parking Facility Parameters through the sections
titled Traffic Parameters, Analysis and Qualitative Guidelines.
9. Meteorological conditions likely to occur during peak use? Use
level during periods of worst meteorology? See section titled Meteorological
Aspects.
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SECTION IX
DATA SOURCES
PUBLICATIONS
1. *The Eno Foundation for Highway Traffic Control. "Parking" 1957.
Saugatuck, Conn.
2. The Eno Foundation for Transportation. "Zoning, Parking and Traffic".
1972. Saugatuck, Conn.
3. Wilbur Smith and Associates. "Parking in the City Center." 1965.
4. Highway Research Record Nr. 317. "Parking Analyses." 1970. Highway
Research Board, National Research Council.
5. Highway Research Record Nr. 395. "Parking Allocation Techniques."
1971. Highway Research Board, National Research Council.
6. Evans, Henry K. "Parking Study Applications." Traffic Quarterly.
April, 1963.
7« Highway Research Record Nr. 237. "Parking." 1968 Highway Research
Board, National Research Council.
8. Peat, Marwick, Mitchell, & Co. "A Guide to Parking Systems Analysis."
For the U.S. Dept. of Transportation. Oct. 1972.
9. Baker, Geoffrey, and Bruno Funaro. "Parking." Reinhold Publishing
Corporation, New York.
10. Automotive Environmental Systems, Inc. A Study of Emissions from
Light Duty Vehicles in Six Cities. EPA Document No. APTD-1497.
March 1973.
11. Maryland Bureau of Air Quality Control. Method for Estimating Light
Duty Vehicle Emission on a Sub-Regional Basis. Report BAQC-TM 73-107.
April 1973.
12. U.S. Environmental Protection Agency. Compilation of Air Pollutant
Emission Factors (Second Edition). EPA Publication No. AP-42,
April 1973.
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13. Holzworth, George C. Mixing Heights, Wind Speeds and Potential for
Urban Air Pollution throughout the Contiguous United States. EPA
Office of Air Programs Publication No. AP-101. January 1972.
PRIVATE COMMUNICATIONS
International Municipal Parking Congress, Arlington, Virginia.
Eno Foundation for Transportation, Saugatuck, Conn.
*Footnote: Figures 5 through 11 should not be reproduced in formal
publications without permission from the Eno Foundation.
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TECHNICAL REPORT DATA
(Please read Instmctions on the reverse before completing)
1. REPORT NO.
EPA-450/3-74-003-d
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Vehicle Behavior In and Around Complex Sources and
Related Complex Source Characteristics
Volume IV - Parking Facilities ;
5. REPORT DATE
October 1973 (Date of issue)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG "\NIZATION NAME AND ADDRESS
Geomet, Inc.
50 Monroe Street
Rockville, MD 20850
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-1094
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Office of Air Quality Planning & Standards
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A general methodology is presented for relating parameters of traffic behavior
at parking facilities, including vehicle running time, facility use rate and
numbers of vehicles running, to more readily available characteristics of the
facilities, including physical layout, number and capacity of entrance and exit
gates, parking capacity and demographic environment. Such relationships are to
be used to relate parking facility characteristics to air quality.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air pollution, parking facilities, urban
planning, traffic engineering, land use,
transportation management,transportation
models, regional planning, urban develop-
ment, urban transportation, vehicular
traffi c
Indirect sources
Indirect source review
13 B
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57
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Unclassified
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