In the second study (Shinar, Rotenberg, & Cohen, 1997) a Monte Carlo computer simulation was used to evaluate the potential crash reduction benefits of the ABWS under different realistic scenarios.
With a total of 7 200 trials, the simulation demonstrated a dramatic decrease in rear-end collisions for the ABWS whenever the headway was 1.
In these situations the ABWS can have no effect on the following driver's behavior or crash prevention.
The second shortcoming of the simulation study is that the relative frequencies of the different scenarios evaluated in the simulation are not known, and therefore the number of rear-end collisions that may be prevented by the ABWS cannot be estimated from the simulation.
Half the vehicles in the study were equipped with ABWS and the other half were not.
The ABWS (treatment) group consisted of 382 vehicles equipped with the ABWS, and the control group consisted of 382 vehicles matched for make and model.
When the lead vehicle is equipped with an ABWS, its brake lights come on as soon as the gas pedal is released.
7 g), the simulation was designed to test the effects of the ABWS on wet roads (cf = 0.
Two dependent measures of ABWS effectiveness were used: (a) the number of crashes prevented with the ABWS versus the number of crashes that would happen without it under the same conditions and (b) average crash severity (in terms of average dV) with and without the ABWS.
There were 120 combinations of vehicle speeds for the two types of roads (2) x headways between the two vehicles (5) x expectancy/alertness levels of the following driver (2) x coefficients of friction between the road and the tires (3) x the presence or absence of ABWS on the lead vehicle (2).
Thus in such cases, assuming the following driver is looking at the car ahead when its brakes are applied, he or she has such a safety margin that the ABWS cannot add any marginal safety benefits.
The point is that had longer times been used, the ABWS benefits would have extended to longer intervehicle headways.