Twin Cities Metro Area Ramp Meter Study
In 2001, MnDOT released the results of an independent study on ramp metering in the Twin Cities metro area. Cambridge Systematics of Cambridge, Mass. evaluated the traffic flow and safety impacts associated with turning off all 430 ramp meters for six weeks as mandated by the 2000 Legislature.
The study began with a five-week pre-study data collection in Sept. 2000 in order for the consultant to compare against the data collected when the ramps would be shut down in Oct. In total, both the "before" and "after" data collection took approximately 12 weeks. Read the May 13, 2002 final report.
- To fully explore the impacts of ramp metering on freeways, local roads, and on transit operations.
- To identify the public perception of ramp metering.
- To compare Minnesota's ramp metering system and timing strategies with other regional systems across the country.
Public involvement a key contributor
Throughout the study process, MnDOT sought guidance from two committees; a Citizens Advisory and a Technical Committee, both of which were charged with representing the public and ensuring the credibility and objectivity of the study. Both committees provided policy oversight, technical guidance, expertise and quality control.
Additionally, to measure customer satisfaction, the consultant used a series of focus groups and telephone surveys to talk to 1,540 users of the system. The consultant sought out individual traveler-oriented perspectives regarding ramp meters and ramp meter operations. See FAQs about the study.
Results presented to MnDOT by Cambridge Systematics showed that without ramp meters there was:
- A 9 percent reduction in freeway volume.
- A 22 percent increase in freeway travel times.
- A 7 percent reduction in freeway speeds, which contributed to the negative effect on freeway travel times. The reliability of freeway travel time was found to decline by 91 percent without ramp meters.
- A 26 percent increase in crashes, which was averaged for seasonal variations. These crashes broke down to a 14.6 percent increase in rear-end crashes, a 200 percent increase in side-swipe crashes, a 60 percent increase in "run off the road" crashes, and an 8.6 percent increase in other types of crashes.
Market research data collection results showed a number of changes in attitudes among area travelers that occurred once meters were shut off, including:
- Most survey respondents believed that traffic conditions worsened.
- Support for modification of the metering system increased from 60 to 70 percent of respondents, and included such changes as using faster cycle times, having shorter operating hours, and using fewer meters.
Actions taken
In 2002, MnDOT launched its new responsive ramp meter timing system to:
- Reduce delays caused by congestion and crashes.
- Reduce the number of crashes caused by congestion.
- Provide travelers with more reliable travel times.
- Manage ramp meter wait times.
A key aspect of the new system was the addition of automated monitoring of wait times at meters so they can be adjusted as needed by MnDOT's traffic management center computers. The new system provides real-time information about ramp delays and limits wait times based on ramp conditions as well as freeway conditions. Specific system features include:
- Ramp meter waits will be no more than four minutes on local ramps and no more than two minutes on freeway-to-freeway ramps.
- Vehicles waiting at meters will not back up onto adjacent roadways.
- Meter operation will respond to congestion and only operate when needed.