Field Evaluation of Variable Advisory Speed Limit System for Reducing Traffic Conflicts at Work Zones

A practical methodology to reduce the traffic conflicts at work zones was developed and evaluated in the field. The proposed system uses variable advisory speed limits that are determined with a two-stage speed reduction scheme. It is designed to lower the speed of the upstream traffic approaching the work zone bottleneck to the same level as the current downstream flow. The system was implemented at one of the I-494 work zones in the Twin Cites, Minnesota, for a three week period in 2006. The data collected from the field indicates 25-35% reduction of the average 1-minute maximum speed difference along the work zone area during the 6:00-8:00 a.m. morning peak periods after the system was implemented. The reduction in speed difference also resulted in approximately 7% increase of the total throughput volume measured at the downstream work zone boundary during the 6:00-7:00 a.m. periods, while the volume increase during 7:00-8:00 a.m. periods was not significant. The estimation of the driver compliance rate by comparing the speed differences upstream and downstream of the advisory speed limit signs showed 20 to 60% correlation levels during the morning peak periods.