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.
A telephone survey was used to poll motorists and assess their reaction to the PTMS. The target survey group included drivers who passed through the I-94 work zone during peak periods when the PTMS were operating and providing system information. The license plates of vehicles that passed through the work zone during PTMS operations were used to establish the sampling frame of potential survey participants.
Sixty-six (66) percent of the drivers surveyed remembered seeing the lighted PTMS DMS messages, and of that group:
- 79 percent remembered one or more specific messages and 99 percent who remembered these messages thought they were "easy to understand."
- 51 percent said they took some action in response to the messages.
- 61 percent said that they were "much more" or "somewhat more" informed about traffic conditions compared to other similar urban work zones.
- 90 percent said they received the traffic information they needed.
PTMS Operator Interview
Two Mn/DOT TMC operators were interviewed. The interviews examined the length of time needed for training, ease of use, usefulness of the system, problems encountered, and suggestions for improvements.
- System operators indicated that the PTMS could be mastered in 2 to 3 hours of training.
- The system was easy to operate and was reliable.
Transit Operations Personnel Interview
Metropolitan Transit Operations personnel were interviewed to determine the extent to which the PTMS affected the transit routes passing through the work zone on I-94.
- Transit operators said the video surveillance feature would be more useful at work zones that experience more significant traffic delays Dispatchers found that the delays anticipated in the work zone on I-94 (up to 20 minutes expected) did not occur.
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