Development and field evaluation of variable advisory speed limit system for work zones

A practical methodology to reduce 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. The system is designed to lower the speed of the upstream traffic approaching the work zone bottleneck to the same level as the downstream flow. The system was implemented at one of the 1-494 work zones in the Twin Cities, Minnesota, for a 3-week period in 2006. Data collected from the field indicated a 25% to 35% reduction of the average 1-min maximum speed difference along the work zone area during the 6:00 to 8:00 a.m. morning peak periods after the system was implemented. The reduction in speed difference also resulted in an approximate 7% increase of the total throughput volume measured at the downstream work zone boundary during the 6:00 to 7:00 a.m. periods. The volume increase during the 7:00 to 8:00 a.m. periods was not significant. 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.