Anti-lock braking system (ABS)

Description
Anti-lock braking system (ABS) prevents the vehicle wheels from locking during hard braking. This allows the driver to maintain the ability to steer the vehicle. In addition, braking distances on slippery surfaces are shorter with ABS.

Impacts
Studies have shown mixed results on the safety effects of ABS. At present, no significant effect on fatal crashes has been found.

Studies

The type of brake system (ABS or conventional) has no significant effect on driving speed under conditions the study was carried out. Authors of the report believe, that behavioural adaptation to ABS is not occurring in "real world" driving situations.	Roadside speed measurements	Mazzae, E. N., Garrott, R. W., Barickman, F., Ranney, T. A. and Snyder, A.	2001	NHTSA Light Vehicle Antilock Brake System Research Program Task 7.1: Examination of ABS-Related Driver Behavioral Adaptation – License Plate Study.
Results related to the safety effects of ABS were contradictory. In 1995 vehicle models with ABS were more likely to be involved in crashes fatal to their own occupants but less likely to be involved in crashes fatal to occupants of other vehicles. Generally, there was no significant effect on fatal crashes. Similar analysis based on accident statistics during 1996-1998 led to different results. Vehicles with ABS were no longer overinvolved in crashes fatal to their own occupants.	Fatal crash rates for passenger cars and vans were compared for the last model year before four-wheel antilock brakes were introduced and the first model year for which antilock brakes were standard equipment.	Farmer, C. M.	2001	New evidence concerning fatal crashes of passenger vehicles before and after adding antilock braking systems. Accident Analysis and Prevention, Issue 33, pp. 361-369
Several statistical crash rate studies have found there to be little or no net safety benefit from four-wheel ABS on passenger cars. Typically these studies have found, that the ABS is associated with a statistically significant decrease in multi-vehicle crashes, a statistically significant decrease in pedestrian strikes and a statistically significant increase in single-vehicle road departure crashes. The safety disbenefit from the third finding approximately cancels the safety benefits from the first two findings.	Results are based on a literature study.	Garrott, R. W. & Mazzae, E. N.	1999	An Overview of the National Highway Safety Administration's Light Vehicle Antilock Brake Systems Research Program. Society of Automotive Engineers (SAE)
Vehicles with ABS were significantly more likely to be involved in crashes fatal to their own occupants but less likely to be involved in crashes fatal to occupants of other vehicles or non-occupants such as pedestrians or bicyclists. Further study is needed to find out, why fatality risk has been increased for occupants of ABS vehicles.	Fatal crash rates for passenger cars and vans were compared for the last model year before four-wheel antilock brakes were introduced and the first model year for which antilock brakes were standard equipment.	Farmer, C. M., Lund, A. K., Tremper, R. E. and Braver, E. R.	1997	Fatal crashes of passenger vehicles before and after adding antilock braking systems. Accident Analysis and Prevention, Vol 29, No. 6, pp. 745-757.