The noble search for the underlying causes of freeway congestion has intrigued traffic engineers for decades. By developing a better understanding of factors causing congestion to form, agencies can respond in a cost effective manner to reduce the impacts. This paper focuses on the results of the analysis of the impact of weather on freeway travel times in greater Seattle, undertaken as part of the SHRP2 L03 work on the causes of congestion. Using the Washington State Department of Transportation (WSDOT) loop sensor volume data and National Oceanic and Atmospheric Administration (NOAA) weather data, average travel times, percent of days congested and 80thand 95th percentile travel times were calculated and compared for rain and no rain conditions. The primary conclusion of this analysis was that disruptions, including rainy weather, cause congestion only when in the presence of sufficient volume. A routinely congested corridor is more likely to show a significant difference in average travel time, 80th percentile travel time and 95th percentile travel time from rain to no rain conditions. In addition, it is only during the peak hours that significant differences in travel time are seen due to rain conditions. Finally, rain has a much greater influence as the peak is building than toward the end of the peak period. Once a roadway was already severely congested, the presence of rain had little impact on travel times. The conclusions of this paper can be used by traffic control centers to improve their operations by usingweather information in the adjustment of ramp metering algorithms and incident response truck staffing.
Samenvatting