AN ANALYSIS OF THE CRASH EXPERIENCE OF LIGHT TRUCKS EQUIPPED WITH ANTILOCK BRAKING SYSTEMS, DOT-HS-808-278, MAY 1995
ABSTRACT
This paper describes the findings from initial analyses of the crash experiences of light trucks and vans (LTVs) equipped with antilock braking systems (ABS).
The objective of ABS is to automatically modulate braking pressure to prevent the vehicle's wheels from locking during braking. Two types of ABS systems are presently available: All wheel (AWAL) and Rear wheel (RWAL). Most of the on-road passenger car (PC) fleet is equipped with AWAL. RWAL ABS is much more prevalent in light trucks and vans (LTV).
The focus of this study was to determine the impact of ABS on specific types of crashes involving LTVs considered to be "ABS relevant", by examining the change in the proportion of crashes in which ABS had the potential to prevent the crash, assuming that the presence or absence of ABS does not affect the occurrence of nonrelevant crashes. Data from NHTSA's Fatal Accident Reporting System (FARS) for calendar years 1989-1993 were used in the analysis. In addition to the FARS data, state crash files from Florida, Maryland, Michigan, and Missouri for the period 1989 - 1991 were used along with the FARS data. Four types of crashes were identified as "ABS-relevant", i.e., crashes for which it was assumed that ABS would be beneficial in avoiding the crash and/or ameliorating the outcome of the crash. The four "ABS-relevant" crash types identified were: (1) rollovers, (2) side impacts with parked vehicles or fixed objects, (3) frontal impacts with parked vehicles or fixed objects, and (4) frontal impacts with another motor vehicle in transport. The analysis examined the experiences for ABS and non-ABS equipped vehicles in the four ABS-relevant crash types, compared to a control group of crashes that were assumed to be unaffected by the presence of ABS. The control group consisted of crashes in which vehicles had rear damage only, e.g., crashes involving vehicles backing into another vehicle or fixed object, non-rollover non-collisions, and other multivehicle crashes that did not involve a frontal impact. The ABS-relevant crashes and control crashes were further classified based upon whether or not the crash occurred under "favorable" or "unfavorable" road conditions. Road surfaces that were paved, free of debris, and dry were considered "favorable." Road surfaces that were wet, snowy, icy, unpaved, or composed of gravel were considered "unfavorable." Tables 1 and 2 summarize the statistically significant findings for AWAL and RWAL LTVs using logistic regression.
| Crash
Severity |
Crash
Type |
Road
Type |
%
Change |
95%
CI |
|---|---|---|---|---|
| All | Roll | Both | - 36 | - 54 to - 10 |
| All | Ror | Both | - 24 | - 40 to - 5 |
| All | Front | Unfav | - 21 | - 33 to - 6 |
| All | Front | Fav | +14 | + 3 to +27 |
| Crash
Severity |
Crash
Type |
Road
Type |
%
Change |
95%
CI |
|---|---|---|---|---|
| All | Roll | Unfav | - 31 | - 36 to - 24 |
| All | Roll | Fav | - 46 | - 51 to - 40 |
| All | Side | Unfav | - 29 | - 36 to - 22 |
| All | Side | Fav | - 15 | - 23 to - 6 |
| All | Front | Both | +11 | + 9 to + 14 |
| Fatal | Front | Both | +32 | +21 to + 43 |
For light trucks and vans, no significant reductions in fatal crashes were found for either AWAL or RWAL-equipped vehicles. While the relatively small sample size of AWAL-equipped vehicles made it more difficult to detect significant reductions in fatal crashes, a significant reduction in non-fatal rollover crashes was associated with the presence of ABS for these vehicles. For RWAL LTVs, significant reductions in non-fatal rollover crashes and side impacts with fixed objects or parked vehicles were found. However, for RWAL LTVs, significant increases in non-fatal and fatal frontal crashes with another vehicle in transport were also found.