Assessment of the Impact of Weather on Freeway Operations in California

Several factors contribute to traffic congestion on highway facilities including adverse weather conditions. However, the extent of weather impacts on traffic flow and congestion delay on freeways is not fully known. This study analyzed an extensive set of historical traffic data from the state of California to gain a better understanding of the proportion of traffic delay that can be directly attributed to weather. A congestion estimation model was developed to estimate vehicle delays directly attributed to rain on 17 urban freeway corridors. It was found that delay due to rain ranged from 3% to 25% of the total delay, and the effects of weather vary significantly depending on both the type of weather and the amount of recurring delay on the freeway segment. Further research in rainfall intensity, evaporation rates on road surfaces, and driver behavior will assist in improving the accuracy of predictions of weather delay and implementation of mitigation strategies.