Precipitation Variation and the Identification of High-Risk Wet Accident Locations in California

To improve safety continually along California's roadways, the California Department of Transportation (Caltrans) developed a list of high-collision concentration locations that required further evaluation and treatment. One version of this list, Wet Table C, analyzes only wet accidents (those during or following precipitation). In developing Wet Table C, wet percent factors–-which quantify the proportion of time per year during which pavement is damp enough to cause traffic accidents (measured on an hourly basis)–-are employed. These factors were originally developed at the county level (i.e., one factor per county). A recent updating of factors allowed for their development at a finer spatial level (quarter-mile segments of roadway). This research examined whether such finer-resolution factors produced different results when incorporated into the Caltrans Wet Table C process. Results of McNemar tests indicated that there was no statistical difference between lists produced using a singular wet percent factor and ones produced using finer resolution factors.