Vehicle Anti-Lock Brake (ABS) Deceleration
Characteristic on Grass
Charles L. Proctor, II, Ph.D., P.E. and Joslyn Hopmayer,
E.I.
Proctor Engineering Research &
Consulting, Inc.
Deceleration characteristics of
vehicles are a critical factor when calculating pre-brake
speed during crash reconstruction and analysis. Absent data
collected at a crash location using a substantially similar
vehicle, investigators must often rely on published data.
Data for deceleration values of tires on common roadway
surfaces is readily available for both traditional and ABS
equipped vehicles, but deceleration data for ABS-equipped
vehicles braking on grass is rarely found in the literature.
Consequently, Proctor Engineering Research & Consulting,
Inc., undertook the challenge of collecting data for
ABS-equipped vehicles braking on grass.
In an effort to represent a spectrum of
common passenger vehicles, this investigation evaluated 6
vehicles in 5 different classes of anti-lock brake equipped
vehicles. The tested vehicles included the following: 2004
Lincoln Navigator, 2002 Toyota Camry, 2002 Mercury
Mountaineer, 1999 Ford F350, 1998 Ford Explorer Sport, and a
1998 GMC Safari. Pre-brake speeds ranged from 23.5 mph to 44
mph. A Valentine Research g-analyst was used to measure the
deceleration of the test vehicles. Testing was done on a
firm bahiagrass surface in a pasture that had not been
plowed or cultivated for several years. This area is typical
off-highway condition found throughout the southeastern
states.
The following table summarizes the individual test results
for the ABS equipped vehicles examined during this
investigation:
|
1998 GMC Safari |
Speed |
Peak Deceleration |
Average Deceleration |
|
Test 1 |
44 |
0.47 |
0.37 |
|
Test 2 |
40.1 |
0.46 |
0.4 |
|
Test 3 |
43.25 |
0.46 |
0.39 |
|
1998 Ford Explorer Sport |
|
|
|
|
Test 1 |
23.5 |
0.41 |
0.38 |
|
Test 2 |
25.2 |
0.45 |
0.39 |
|
Test 3 |
26.4 |
0.45 |
0.4 |
|
1999 Ford F350 |
|
|
|
|
Test 1 |
27 |
0.43 |
0.39 |
|
Test 2 |
28 |
0.45 |
0.41 |
|
2002 Mercury Mountaineer |
|
|
|
|
Test 1 |
25.2 |
0.45 |
0.39 |
|
Test 2 |
31.1 |
0.53 |
0.48 |
|
Test 3 |
29 |
0.51 |
0.45 |
|
Test 4 |
38.4 |
0.56 |
0.43 |
|
2002 Toyota Camry |
|
|
|
|
Test 1 |
23.5 |
0.46 |
0.42 |
|
Test 2 |
23.5 |
0.48 |
0.44 |
|
Test 3 |
25.5 |
0.47 |
0.43 |
|
2004 Lincoln Navigator |
|
|
|
|
Test 1 |
33.3 |
0.53 |
0.45 |
|
Test 2 |
33.1 |
0.53 |
0.46 |
|
Test 3 |
33.9 |
0.54 |
0.46 |
|
Test 4 |
31.4 |
0.52 |
0.43 |
Comparison of average deceleration and initial speed is
presented in the following figure.
What we find from examination of these
data is that no consistent vehicle type or speed trends are
observed. In other words, all the vehicles, regardless of
type or size, behaved similarly within the speed range
tested. Looking at the data as a whole, one can observe that
the combined average grass deceleration value from all data
is 0.42g with a standard deviation of 0.06g. As such, it is
reasonable to assume a deceleration rate of 0.42g for
anti-lock brake equipped vehicles under hard braking over an
off-road firm bahiagrass surface.
