This Phase II study was conducted as a follow up study to a Phase 1 study that found that radar equipped dynamic message signs (DMS) are more effective than Uniform Traffic Control Devices (MUTCD) signs at reducing vehicle speeds in work zones during construction projects that last one week or less. The purpose of the Phase 2 study was to confirm the findings of the Phase 1 study and evaluate the effectiveness of radar equipped DMS at reducing vehicle speeds in work zones in place up to seven weeks.

Radar equipped DMS can be used to display specific warning messages to drivers if vehicle speeds are detected above preset threshold levels. This strategy was implemented for several weeks at three test sites (I-81 South at Bristol, I-81 North at Bristol, and US 19 North at Lebanon, Virginia). Pneumatic road tubes and automated traffic counters were installed to collect vehicle speed and traffic volume data at the beginning, middle, and end of each work zone.

The DMS units were placed a short distance behind the first set of road tubes and the radars were set to detect the speeds of incoming vehicles at a distance of about 400 ft to 600 ft away. When a speeding vehicle was detected the DMS was programmed to flash the message "YOU ARE SPEEDING SLOW DOWN."

Data collection was carried out over several weeks to study the effect of duration of DMS deployment on vehicle speeds during the construction season of 1995 and 1996.

Based on a statistical analysis of the data collected with and without DMS messages the study found that radar equipped DMS can reduce vehicle speeds by 8 to 9 mi/hr. The authors note that the presence of the data collection team caused marginally lower speeds (0.5 to 2 mi/hr) compared to when the team was not on-site, however, this did not negate the result on the effectiveness of the DMS. Statistical tests on the effect of duration of exposure showed that the speed reductions were still significant after seven weeks of exposure.