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The influence of anti-lock braking systems (ABS) on relative crash risk is examined by comparing the ratio of the number of crashes under an adverse condition (say, when the pavement is wet) to the number of crashes under a normal condition (say, when the pavement is dry) for vehicles with and without ABS. The study used seven General Motors passenger vehicles having ABS as standard equipment for 1992 models but not available for 1991 models. Crashes in 1992 and 1993 in Texas and Missouri were analyzed. After correcting for model year effects not linked to ABS, etc., the following associations between ABS and crash risk were obtained (the errors are one standard error); a (13 ± 4)% lower crash risk on wet roads (assuming no change on dry roads); a (13 ± 5)% lower crash risk when it is raining (assuming no change under clear weather); a (34 ± 15)% lower risk of a pedestrian crash (assuming no change for non-pedestrian crashes).

Speed-time data obtained in two large-scale studies by following randomly selected vehicles in a number of cities with an instrumented car are analyzed here by dividing the data into trip segments between successive stops and computing values of traffic variables for the individual trip segments. Results from the two studies are found to be in good agreement. The analysis focuses on variables previously shown to be related to fuel consumption, particularly on the relationship between energy used to accelerate the vehicle, energy dissipated in braking, and mean traffic speed. Braking and acceleration are found to play a major role in determining tractive energy requirements in low speed urban driving, since about half the energy supplied to the wheels is used to accelerate the vehicle, and about two-thirds of the resulting kinetic energy is dissipated in braking.