Knowledge Resources

The Minnesota Department of Transportation (Mn/DOT) used Portable Traffic Management Systems (PTMS) to minimize traffic delays and improve safety at work zones on I-94 between Minneapolis and St. Paul, Minnesota, and on I-35 located south of the Twin Cities. The equipment at each site consisted of trailer mounted dynamic message signs (DMS), and multiple PTMS units equipped with mast mounted DMS and digital surveillance cameras. The DMS trailers and PTMS units were connected to the Mn/DOT transportation management center (TMC) using wireless communications and the telephone network.

The PTMS used machine vision technology to monitor traffic conditions, detect incidents, and provide TMC operators with real-time video, and traffic speed and volume data. The incoming data were analyzed by TMC operators who were responsible for activating appropriate messages on DMS to control traffic and inform motorist of prevailing conditions in the work zone. The data and images collected were also posted on a traveler information website.

Traffic data were collected at the I-94 site for approximately 35 days in July and August, 1996 where the PTMS was operational for approximately 18 days (during morning and afternoon peak periods only). Traffic data were collected at the I-35 site for approximately 30 days in September and October, 1996 where the PTMS operational for approximately 8 days (during morning peak periods only).

The PTMS was evaluated by assessing technical performance and determining system impacts. This was accomplished by collecting traffic data before and after the system was made operational, and evaluating customer satisfaction survey data collected from motorists who experienced the system. In addition, interviews were conducted with TMC operators and transit professionals to evaluate operational aspects.

Speed information from machine vision cameras was used to evaluate the effects of PTMS on the work zone traffic conditions. This involved assessing changes in the variability of the speeds and changes in the average speed in each work zone.

FINDINGS

PTMS reduced the average speed of traffic approaching the work zone by nine miles per hour and decreased the variability of vehicle speeds within the work zone by approximately 70 percent.