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Validate Percent Wet Time Statewide

Project #: 4W1040
Start Date: 05/18/2006
End Date: 03/31/2008
Status: Completed

To plan for safety improvements, Caltrans develops a list of high concentration collision locations (Table C) every quarter using the Traffic Accident Surveillance and Analysis System (TASAS) database. Table C identifies the ramps, intersections and highway segments with accident rates that are significantly higher than the statewide average. Caltrans also develops a Wet Table C annually that analyzes wet accidents alone, using a similar methodology as Table C. The existing table of percent wet time table (percentage of time the pavement is wet) was developed in 1972, using data from 1957-67. Recent research on precipitation patterns indicate that the percent wet time table from 1972 does not reflect the current percent wet time and needs to be updated. Incorrect wet percent time factors could result in locations not being identified for safety investigations as well as incorrect locations being identified for investigation. It is critical that all high wet collision locations are identified, because approximately nine percent of fatal collisions in California occurred on wet pavement conditions in 2003. This project will collect and analyze data to update the wet percent factors used in the development of Wet Table C. In addition, the research will investigate methods to improve the accuracy and precision of the tables.


To improve and update the data and tables used by Caltrans to identify locations with a high concentration of accidents on wet pavements.