EPA-AA-LDTP-75-3
Comparison of the Vehicle Operational Characteristics
of the EPA Highway Dynamometer Driving Schedule
with the Rural Driving Data Collected by the
GM CHASE Car Survey
by
Elwood W. Vogt
September, 1975
Environmental Protection Agency
Office of Air Programs
Office of Mobile Source Air Pollution Control
Emission Control Technology Division
Standards Development and Support Branch
Ann Arbor, Michigan 48105
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Comparison of the Vehicle Opertional Characteristics of the EPA Highway
Dynamometer Driving Schedule with the Rurnl Driving Data Collected by
the GM CHASE Car Survey.
According to statistics provided by the Federal Highway Adminis-
tration (FHWA), rural travel accounts for approximately 45% of the total
vehicle miles accumulated by motor vehicle operation in the United
States (1) . Because the EPA Urban Dynamometer Driving Schedule (EPA
UDDS) represents only the type of driving encountered in an urban
environment, the EPA Highway Dynamometer Driving Schedule (EPA HDDS),
developed in 1974, is a desirable supplement to the procedure for
measuring fuel economy. The EPA HDDS is constructed from actual speed
versus time traces that were generated by driving an instrumented test
car over a variety of non-urban roads and highways (2). This schedule
reflects the correct proportion of operation on each of the four major
types of rural roads (as categorized by the FHWA) and preserves the non-
steady-state characteristics of real-world driving (2).
Outside urban areas, the FHWA has delineated the following distinct
road types as the basis for their functional classification scheme of
rural roads and highways.
A. Principal arterial system
B. Minor arterial system
C. Collector system
D. Local system
The categorization of roads in a rural system begin at the top of the
hierarchy and works down. First, the principal and minor arterial
systems are designated on a statewide basis. Then, the collector and
local road classifications are developed from a more localized (county)
perspective.
In Table 1, the percentages of total highway vehicle miles travelled
in the United States on each of these four types of roadway are expressed (2)
Significantly, these percentages formed the basis for the construction
of a composite highway driving schedule to simulate all modes of highway
operation (2).
Table 2 presents a compilation of both the individual road type and
composite highway trip operational characteristics that were established
as goals to be achieved when designing the highway schedule (2).
During the formulation of the highway schedule, the decision was
made to combine segments of actual on-road traces to representing travel
on each of the different road types to compose the schedule (2). Addi-
tionally, the most realistic sequence of segments was found to be DCAB.
The schedule starts from an idle, contains four major speed deviations (one
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each in B and D, two in C), and ends with a deceleration to a stop and
idle. Two-second idle periods are included at both the beginning and
the ending of the schedule (2).
Table 3 provides a compilation of the operational characteristics
for both the individual road type segments and the composite EPA HDDS (3).
In compliance with the original objective,) the results are quite similar
to the figures furnished in Table 2.
During 1974, General Motors (GM) collected, as part of their CHASE
Car survey, approximately 1700 miles of non-urban vehicle operational
data. By using the chase car technique, GM attempted to gather light-
duty vehicle operational data representative of urban and rural driving
throughout the United States. Simply, the chase car method, entails
following randomly selected vehicles with an instrumented vehicle and
duplicating the operational behavior of each as precisely as possible.
To facilitate statistical analysis, GM filtered the rural driving date
by road type and these results will be referred to in this report as GM
Rural RT (GM rural driving data filtered by road type). Table 4 supplies
the operational characteristics for each of these individual road types,
as well as the entire GM Rural RT data set.
Significantly, 98% (Table 4) of the mileage accumulated in non-
urban locations was driven on roads classified by GM as either Rural
Highway or Expressway. In contrast, the FHWA determined that only 62%
(Table 1) of rural driving mileage in the U.S. is amassed on principal
and minor arterial roads. Even though the GM road types cannot be
correlated with FHWA road classifications on a one-to-one basis, these
figures indicate that the GM chase cars did not travel enough on col-
lector and local roads. As a result, an unusually high overall average
speed is the expected tendency in the composite GM rural data, because
principal and minor arterial systems have higher average speeds than do
collectors and locals (see Table 2). In this respect, the GM Rural RT
data may be biased. Conversely, though GM's chase cars seem to have
driven few miles on roads that are categorized as collectors and locals
(i.e. Unpaved-Rural, Unpaved-Suburban, and Suburban-No Curb), the
average speeds they found on these road types are much lower than the
speeds predicted by the FHWA data. Comparing the average speed and
stops/mile data of Tables 2 and 4, Rural Highway statistics resemble
those of FHWA collectors while Expressway statistics seem to be an
average combining those or principal and minor arterial roads.
The purpose of this report is to compare vehicle operational
characteristics of the EPA highway cycle with those of the GM Rural RT
data. The computer program developed by GM to evaluate the rural GM CHASE
Car data was also employed to analyze the highway schedule. Therefore,
driving characteristics for both the GM Rural RT data and EPA HDDS were
tabulated according to common criteria. Initially, the more easily
calculable parameters such as average trip length, average trip duration,
and average trip speed shall be contrasted for the EPA HDDS and GM Rural
RT data. As seen in Table 5, the values are quite similar.
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Stops/mile is the next parameter to he compared (Table 6). This Is
important in that average trip speed will decrease as stops/mile is
increased. CM established three different categories of stops-rolling
(similar to a vehicle rolling through a stop sign), noisy (vehicle stops
in heavy traffic and moves ahead several times before clearing an intersection),
and full (vehicle stops at a stop sign and then proceeds when the inter-
section clears) (5). Significantly, the EPA HDDS has more noisy and
full stops per mile than the GM Rural RT data.
The percentages of miles and time spent in various speed bands
indicate that the EPA HDDS has most of its driving around 45, 50 or 55
mph, while vehicle speeds are more evenly distributed in the GM Rural RT
data. GM's chase cars also monitored a substantial amount of vehicle
operation above 60 mph. The same trends can be seen by contrasting the
percentages of miles and time spent in the different speed bands when
cruising. GM defined cruising as an acceleration/ deceleration of less
than + 0.05 G's. These data are contained in Tables 7-10.
A comparison of the percentages of miles and time spent in various
acceleration and deceleration bands reveals that the GM Rural RT data
and EPA HDDS have very similar acceleration/deceleration patterns. The
basis difference found is that the highway cycle confines acceleration
to only two bands and deceleration to three bands (i.e. a small span)
while a small portion of the acceleration and deceleration in the GM
Rural RT data is again spread over a wide range of values. Otherwise,
the acceleration and deceleration percentages seem to be quite similar.
These data are contained in Tables 11-14.
Contrast of the operational mode summaries (Table 15) indicates
that the EPA HDDS has slightly greater percentages of miles and time in
both the idle and cruise modes, while GM Rural RT data show larger
percentages of miles and time in the acceleration and deceleration
modes.
In conclusion, comparison between the EPA HDDS and GM Rural RT data
seems to suggest that both have very similar operational characteristics,
most notably average trip speed. The primary discrepancies found are
that the highway cycle has more stops/mile and the GM Rural RT data
includes substantial driving at speeds above 60 mph. Because types of
roadway are defined differently by General Motors and the FHWA, it is
difficult to determine whether the percentage of miles driven on each
road classification by the chase cars are comparable to.those found in
the EPA highway schedule. However, assuming that GM's definitions of
Rural Highway and Expressway are synonymous with the concept of an
arterial, it seems that GM's chase cars drove too much on principal and
minor arterials and not enough on collectors and locals.
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References
1. T.C. Austin and K.H. Hellman, "Passenger Car Fuel Economy as In
fluenced by Trip Length", Paper 750004, presented at SAE Automotive
Engineering Congress and Exposition, Detroit, Michigan, February,
1975.
2. R.E. Kruse and C.D. Paulsell, "Development of a Highway Driving
Cycle for Fuel Economy Measurements", Environmental Protection
Agency, March, 1974.
3. C.D. Paulsell, "Amendments to the Report on Development of a
Highway Driving Cycle for Fuel Economy Measurements", Environmental
Protection Agency, April, 1974.
4. T.C. Austin, K.H. Hellman, and C.D. Paulsell, "Passenger Car
Fuel Economy During Non-Urban Driving", Paper 740592, presented
at SAE West Coast Meeting, Anaheim, California, August, 1974.
5. T.M. Johnson, D.L. Formenti, R.F. Gray, and W.C. Peterson, "Measure
ment of Motor Vehicle Operation Pertinent to Fuel Economy", Paper
750003, presented at SAE Automotive Engineering Congress and Ex
position, Detroit, Michigan, February, 1975.
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Appendix
Table 1
Type of Highway
A. Principal arterials
B. Minor arterials
C. Collectors
D. Locals
Percent of Highway
Vehicle Miles Travelled
Table 2
Average Highway Characteristics
Road Type
A
B
C
D
Composite Trip
Average Speed
(mph) Stops/mile
57.16
49,42
45.80
39.78
49.43
0.0100
0.0575
0.1260
0.2360
0.08
Segment Length Percent of
(miles) Total Miles
3.91
2.22
2.37
1.41
9.91
39.46
22.40
23.92
14.23
100.0
Road Type
Segment
Idle
D
C
A
B
Idle
EPA HDDS
Average Speed
(mph)
0.00
40.74
43.84
56.11
48.23
0.00
48.20
Table 3
Stops/mile
One stop
for the
entire cycle
0.098
Segment Length
(miles)
0.00
1.63
2.11
3.97
2.53
0.00
10.24
Percent of
Total Miles
0.00
15.91
20.57
38.80
24.72
0.00
100.0
Segment
Duration
(seconds)
2
144
173
255
189
2
765
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Table 4
Characterization of Composite GM Rural RT Data Set
Road Type
Average Speed
(mph)
Stops/Mile Miles Travelled
Percent of
Total Miles
Rural High-
way 44.70
Expressway 53.12
Vnpaved-Rural 24.50
Unpaved-Subur-
ban 17.71
Suburban-
No Curb 21.45
GM Rural RT 49.08
0.100
0.034
0.546
0.739
0.964
0.069
488
1184
5
25
1705
28.63
69. LL
0.29
0.18
1.47
100.00
Table 5
Average Trip Length (miles)
Average Trip Duration (minutes)
Average Trip Speed (mph)
EPA HDDS
10.24
12.75
48.20
GM Rural RT
8.66
10.58
49.08
Table 6
Rolling Stops/Mile
Noisy Stops/Mile
Full Stops/Mile
Noisy & Full Stops/Mile
Total Stops/Mile
EPA HDDS
0
0.191
0.191
0.382
0.382
GM Rural RT
0.093
0.060
0.069
0.129
0.222
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Table 7
Percentage of Miles Spent in Speed Bands
mph ± 2.5 mph 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
EPA HDDS
GM Rural RT
.05
.01
.08
.10
.10
.21
.22
.39
.24
.85
.68
L.26
1.47
2.22
3.54
3.34
8.11
5.71
26.41
8.59
17.72
16.08
38.02
24.68
3.37
20.08
0
9.14
0
5.37
0
1.24
Speed Range
(mph)
0-42 . 5
42.5-57.5
57.5-77.5
EPA HDDS
14.49
82.15
3.37
GM Rural RT
14.09
49.35
35.83
mph ^2.5 mph 0
Table 8
Percentage of Time Spent in Speed Bands
10 15 20 25 30 35 40 45 50
55
60
65
70
75
EPA HDDS
GM Rural RT
4.07
1.25
.51
.96
.38
1.01
.64
1.27
.51
2.07
1.14
2.46
2.16
3.62
4.57
4.65
9.02
6.97
26.43
9.33
16.26
15.68
31.64
22.06
2.67
17.13
0
6.92
0
3.79
0
.83
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mph +2.5 mph
Table 9
Percentage of Miles Spent in Speed Bands While Cruising
5 10 15 20 25 30 35
0000
05 .09 .15 .4
Speed Range
(mph)
0-42.5
42.5-57.5
57.5-77.5
.33 1.08 3.07
8 .82 1.68 2.78
EPA
40 45 50 55 60
7.42 26.89 18
5.20 8.18 16
HDDS
11.90
84.58
3.51
.05 39.64 3.51
.34 25.80 21.85
GM Rural RT
11.25
50.32
38.41
Table 10
Percentage of Time Spent
in Speed Bands While Cruising
65
70
75
mph +2.5 mph 0 5
10
60
65
70
75
EPA HDDS
.-GM Rural RT
0
0
0
.48
0
.44
0
.52
0
1.23
.57
1.67
1.70
2.87
4.25
4.07
8.78
6.68
28.75
9.34
17.71
16.76
35.27
24.25
2.97
18.93
0
7.64
0
4.20
0
.92
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Table 11
Percentage of Miles Spent in Acceleration Bands
G's
.05-.10 .10-.15
,55-.60 .60-.65
EPA HDDS
GM Rural RT
83.68
82.51
16.32
11.81
4.84
.57
.09
.12
.02
0
.04
A
v^
0
0
G's
.05-.10 .10-.15
Table 12
Percentage of Time Spent in Acceleration Bands
.15-.20 .20-.25 .25-.30 .30-.35 .35-.40 .40-.45 .45-.50
50-.55 .55-.60 .60-.65
EPA HDDS
GM Rural RT
75.00
76.87
25.00
14.77
6.98
1.02
,14
.16
.02
0
.04
0
0
0
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G's
.05- .10
.10- .15
Table 13
Percentage of Hllea Spent In Deceleration Bands
.15-".20 ~.20-~.25 ~.25-~.30 ~.30-~.35 ~.35-~.40 ~.40-~.45 ~.45-~.50 ~.50-~.55 ~.55-~.60 ".60-".65
EPA HDDS
CM Rural RT
76.71
77.94
16.89
13.68
6.40
6.47
1.42
.34
.09
0
0
.03
0
.03
0
G's
.05- .10
.10- .15
.15- .20
Table 14
Percentage of Time Spent in Deceleration Banda
.20-".25 ~.25-~.30 ~.30-~.35 ~.35-~.40 ~.40- .45
.45-".5J ~.50-~.55 ".55- .60 . .60- .65
EPA HODS
CM Rural RT
73.53
70.33
20.59
17.55
5.88
9.45
2.03
.49
.13
0
0
.01
0
.01
0
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Table 15
Operational Mode Summary
EPA HDDS
GM Rural RT
Operating Mode
Idle
Cruise
Acceleration
Deceleration
Percent Miles
in Mode
0
95.90
1.32
2.78
Percent Time
in Mode
3.A3
89.71
2.54
4.32
Percent Miles
in Mode
0
93.45
3.02
3.55
Percent Time
in Mode
1.10
88.84
4.47
5.60
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