A Study of the Effectiveness of Unmanned Radar as a Speed Control Technique in Freeway Work Zones

The focus of highway work is shifting from new construction further into maintenance, rehabilitation, and reconstruction of existing facilities. Work zones constitute sections of highway where these efforts are actively pursued. Excessive speed is often a contributing factor to work zone accidents. One method of speed control in work zones is the deployment of unmanned, or drone, radar transmitters, to simulate and supplement police presence in work zones.

A review of the literature and past research on speed control techniques was conducted, and data was collected in several work zones on Interstate 81 in Virginia. Traffic data were gathered both upstream and in the range of the unmanned radar units. Effectiveness of the unmanned radar was expressed as changes in mean speed, speed variance, percent of traffic exceeding the speed limit, and eighty-fifth percentile speed. Statistical analyses on the resulting speed distributions utilized hypothesis testing to determine the significance of differences in the measures of effectiveness among speed control conditions in work zones. User costs associated with work zones were also examined.

At the sites studied, significant reductions in mean speed and in percent of traffic exceeding the speed limit were observed, as were minor reductions in speed variance and eighty-fifth percentile speed. Unmanned radar was found to be particularly effective when police presence was expected by motorists. From this research effort, recommendations were developed to assist traffic engineers in determining the most effective way to use unmanned radar to maximize their safety benefit on the traffic stream.