Vehicle Deceleration Levels during Wet-to-Dry Transitions on an Asphalt Surface with a High Proportion of Aggregate

The goal of this study is to quantify how the braking performance of newer anti-lock braking systems (ABS) changes as the level of road wetness varies on an asphalt road surface with a high proportion of aggregate present in the asphalt matrix. To achieve this goal, we conducted 375 straight-line braking tests using a late-model sedan and SUV on a public road in Mississauga, ON. Each vehicle was equipped with a 5th wheel (resolution 0.1 mm) sampled at 200 Hz, from which vehicle speed and deceleration were calculated. The road surface was wetted four times and allowed to dry each time under ambient conditions over a period of about one hour. As the road transitioned from wet to dry, a continuous series of ABS-braking tests were performed from an initial speed of 60 km/h. Both the maximum and average decelerations for each braking event were compared between six “wetness” categories assigned to the road surface condition present for each test. We found that the vehicles were able to decelerate at over 0.8 g when the road was fully wet. This deceleration remained relatively constant as the road surface dried, and then suddenly increased to between 0.9g and 1.0 g when the road was about 50% dry. These findings are similar to those reported last year on asphalt with very little aggregate, and show that the amount of aggregate in the asphalt matrix has little or no effect on wet and dry ABS-braking performance. This study provides additional support for the high deceleration levels that can be achieved by modern ABS-equipped vehicles on wet roads.