Evaluation of Wet Weather Accident Causation Criteria

This report documents findings from analysis of traffic collision data from sites that display high collision rates only under wet pavement conditions. These sites were selected using Caltrans safety engineers’ field reports, Wet Table C “investigation required” locations, and a new approach called Continuous Risk Profile (CRP).The geometric features at the sites were studied via field visits and review of as-built plans. Rapid spatial changes (i.e., vertical and horizontal curve in short distance), narrower lane width, lack of median, and wider total freeway width were some of the notable geometric features observed at these sites. There were also other features found to be responsible for diminishing drivers’ visibility. These features are explained in detail with the aid of photographs taken during the field visits.Findings showed significant differences in wet and dry collision distribution across traveling lanes at some locations. Speeding remained the primary collision causative factor regardless of pavement condition, but was more dominant under wet than dry pavement conditions at all observed locations.