AN ANALYSIS OF THE CRASH EXPERIENCE OF PASSENGER CARS EQUIPPED WITH ANTILOCK BRAKING SYSTEMS, DOT-HS-808-279, MAY 1995
ABSTRACT
This paper describes the findings from initial analyses of the crash experiences of passenger cars (PCs) 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 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 PCs 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, Missouri, and Pennsylvania for the period 1989 - 1993 were used, along with data from Maryland for the period 1989 - 1992. 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." The following Table summarizes the statistically significant findings, using logistic regression.
| Crash
Severity |
Crash
Type |
Road
Type |
%
Change |
95%
CI |
|---|---|---|---|---|
| All | Roll | Both | +24 | + 6 to + 45 |
| All | Ror | Both | +15 | + 9 to + 22 |
| All | Side | Both | +36 | +25 to + 48 |
| All | Front | Unfav | - 35 | - 39 to - 32 |
| All | Front | Fav | - 9 | - 11 to - 7 |
| Fatal | Roll | Both | +60 | +21 to +111 |
| Fatal | Side | Both | +91 | +44 to +154 |
| Fatal | Front | Unfav | - 35 | - 52 to - 11 |
Several findings for passenger cars are noteworthy; while a significant reduction in non-fatal frontal impacts with another motor vehicle in transport crashes was found to be associated with the presence of ABS, significant increases in non-fatal frontal and side impacts with parked vehicles or fixed objects were also found to be associated with the presence of ABS. For fatal crashes, significant increases in rollover and side impacts with parked vehicles or fixed objects were also found.