An anti-lock braking system (ABS) prevents the wheels from locking, which results in a more stable road handling and manoeuvrability. Crash study reviews [12] [76] show that the presence of ABS goes hand in hand with a significant decrease in multiple crashes on wet or poor road surfaces, crashes with turning vehicles, and crashes with pedestrians, cyclists and animals. However, the presence of ABS also goes hand in hand with a significant increase in single-vehicle crashes (among which rolling over and colliding with a fixed obstacle). According to Elvik et al. [12], who looked at crash outcome, the net effect of ABS on road safety is a decrease in injury crashes (-1%), but also an increase in fatal injury crashes (+6%).
The increase in single-vehicle crashes due to ABS has not yet been conclusively explained. Burton et al.[29] mention two principles that may be at play: behavioural adaptation and excessive steering to prevent a crash. A German crash study, for example, found an indication of behavioural adaptation: drivers of cars with ABS drove faster and more aggressively [77]. Based on speed measurements in daily traffic, however, an American study did not find higher driving speeds for vehicles with ABS [78]. If braking is accompanied by excessive steering, the vehicle runs the risk of rolling over due to the extra grip because of ABS. This risk seems to be reduced by the introduction of electronic stability control (ESC); a system that builds upon ABS (see the question What is the road safety effect of electronic stability control (ESC)?).
For cars in Europe, ABS is not mandatory. Yet, once it has been implemented, the European vehicle guidelines in UN/ECE 13H apply. Partly thanks to the development and mandation of electronic stability control (ESC), which uses ABS technology, ABS has indirectly become mandatory for new cars too.