Estimation of Winter Snow Operation Performance Measures with Traffic Flow Data, Phase 2

Project summary:

The ability to accurately and reliably estimate the performance of winter maintenance activities is critical for improving the efficiency and effectiveness of Minnesota Department of Transportation operations. Phase 1 of this research produced a prototype process to estimate the speed variation points during recovery periods for given routes using the traffic flow data collected from field detectors. In this Phase 2 project, the prototype process was enhanced with the expanded data set and traffic-data-based alternative measures were developed for snow maintenance operations. The enhanced process were applied to selected snow events in the metro freeway network to estimate those measures for the selected routes. An automatic process was developed to determine the normal condition regain time (NCRT) using the traffic flow data for a given snow event. To reflect the different traffic flow behavior during day and night time periods, two types of the normal conditions were defined for each detector station. The normal condition for day time was defined with the average speed-density patterns under dry weather conditions, while the time-dependent average speed patterns were used for representing night time periods. In particular, the speed-density functions for the speed recovery and reduction periods were calibrated separately for a given location to address the well-known traffic hysteresis phenomenon. The resulting NCRT estimation process determined the NCRT as the time when the speed level on a given snow day recovers to the target level of the normal recovery speed at the corresponding density for the day time periods. The sample application results with the snow routes in the Twin Cities, Minnesota, show the promising possibilities for the estimated NCRT values to be used as the reliable operational measures, which could address the subjectivity and inconsistency issues associated with the current bare-lane regain times determined through visual inspections.