Twin Cities Metro Area Ramp Meter Study FAQs
MnDOT shut down all 430 meters in the Minneapolis/St. Paul area on Oct. 16, 2000. The shutdown was part of a legislative mandate that required MnDOT to study the effectiveness of ramp meters. The meters have remained off for the required six-week period. Data has been collected and is being analyzed in preparation for presentation to the Legislature by Feb. 1, 2001.
Dec. 2000 FAQs
Based on input received from technical and advisory committees, the consultant team and preliminary data from the study, Transportation Commissioner Elwyn Tinklenberg made a series of decisions to be implemented Friday afternoon, Dec.8, 2000. With the changes, ramp meters will be on for a shorter period of time during rush hours, meters will change more quickly from red to green and several meters will remain off.
The hours of ramp meter operation will be limited to 6:30 - 8:30 a.m. and 3:30 - 5:30 p.m. Although the meters can come on between these hours, ramp meters are traffic activated and will come on only if certain congestion thresholds are met. Prior to the shutdown, meters were operating 6:00 - 10:00 a.m. and 2:30 - 7:30 p.m. Metering will range between 2 and 15 seconds per vehicle, depending on conditions. These measures will be applied system wide. During the morning hours, 60 of 273 operating meters will remain off and 63 of 329 operational meters will remain off in the afternoon. These ramp meters will flash yellow.
MnDOT anticipates that the modifications will be in effect at least until the ramp meter study is presented to the Legislature on Feb.1, 2001. During this time the department and its consultant team will collect new data generated by the system modifications. While it is difficult to project how long these modifications will be in place, they are likely to be the first in a series of modifications that will determine how ramp metering evolves in the metro area.
It has become clear that an all or nothing approach is not the best. MnDOT is seeking balance between safety, efficiency and public consensus. Preliminary market research shows that 20 percent of commuters want the meters left off. A small percentage wants the ramp meters on as before. However, the majority of commuters, about 70 percent, want the ramp meters modified. They want fewer meters, shorter operating hours and faster lights.
Data collected before the meters were turned off and preliminary findings in recent weeks indicate that some meters could remain off. The commissioner made the decision based on expert third party advice and input from technical experts, community leaders and others.
Meters that will remain off during the modification period were selected on one of four possible criteria:
- Ramp is low-volume, experiencing less than 400 cars per hour.
- Ramp is extremely high volume, making it difficult to manage effectively. An example is northbound 35W to westbound 94 in Minneapolis.
- Ramp is atypical. An example is Portland Avenue to eastbound Highway 62 where it is the sole meter in the zone - it doesn't "fit" with the upstream or downstream zones in the area.
- Ramp does not operate often because congestion does not meet the minimum "turn on" thresholds.
The commissioner will make that decision after the data from the study is compiled and analyzed. This will include congestion delays, traffic speeds, fatal and non-fatal crashes and public opinion research. The commissioner will also consider information gained from modifications.
MnDOT will continue to try to strike a balance between safety, efficiency and public consensus. Changes may be made from time to time as the department learns what impact modifications have on specific locations and system wide.
Ramp meters are not a long-term solution to congestion. In 1982, according to the Texas Transportation Institute, the Twin Cities area was the 43rd most congested region in the country. By 1997, the area had moved to 14th or 19th, depending on the survey used. Projections indicate that congestion continues to accelerate and the region continues to grow.
The actual turn-on of meters is based on a set of complex mathematical formulas called algorithms which take into account various congestion level thresholds - including volume data (information on the numbers of vehicles actually traveling through the system). These data are gathered by 3700 loop detectors (sensors) located in the pavement throughout the Metro area. These sensors are polled once every 30 seconds by a computer at the Traffic Management Center which then automatically either activates a meter, or determines it should remain in a flashing yellow mode.
System-wide there are 430 metered ramps. However, in the morning when traffic is primarily "inbound" or moving suburb to suburb, a total of 213 ramps can be turned on. In the evening, when traffic is primarily "outbound", a total of 266 metered ramps can be activated to flash green, yellow, and red.
During those hours when ramp meters can be activated (6:30 to 8:30 in the morning and 3:30 to 5:30 in the evening), they will do so based on volume/congestion thresholds which when met trigger the start-up of a meter. These thresholds are based on the number of vehicles entering the freeway in a particular area (or zone) and the number of vehicles already on the freeway in that same zone. (To help it better manage the freeway network, MnDOT has divided it into 93 zones, each between three and five miles long).
Under the recently enacted ramp meter modifications, when a zone becomes so congested that metering would no longer be helpful to the efficient movement of traffic through it, the zones meters will simply continue to flash yellow. If congestion thresholds in a specific zone are met prior to the start of ramp meter operating hours, the meters in that zone will continue to flash yellow throughout the rush hour.
Prior to the ramp meter shutdown, and prior to the recently enacted modifications, there were six different metering rates that could be applied at any given meter, at any given time during the morning and evening rush hour. The range of red times for each of those rates - excluding the 2-second yellow/green time was:
Rate 1 = from 0.1 to 11.3 seconds
Rate 2 = from 0.1 to 13.4 seconds
Rate 3 = from 0.1 to 16.2 seconds
Rate 4 = from 0.1 to 18 seconds
Rate 5 = from 0.3 to 18 seconds
Rate 6 = from 0.6 to 18 seconds
The modifications currently under study call for metering rates to be capped at Rate 2.
Rate 1 = red time ranges from 0.1 to 11.3 seconds
Rate 2 = red time ranges from 0.1 to 13.4 seconds
Note: The actual red time for a specific ramp is based on the number of vehicles that use that ramp in a given hour. The higher the volume on the ramp the lower the red time used for the ramp.
MnDOT's decision to "cap" metering rates at rate 2 reflects input it received from numerous sources, including daily rush-hour commuters, the consultant team working on the study, the ramp meter shutdown study's Citizen's Advisory and Technical Committees, and traffic management and engineering experts from within the Department. It was clear, based on all that impact, that Mn/DOT's ramp metering strategy and policy could not be the same as it was during pre-shutdown conditions.
Mn/DOT will continue to rely on outside expertise to help it develop and implement technically sound ramp meter strategy, policy and modification evaluation plans and to review and validate the results of those evaluations. Travel time, safety, travel time reliability, throughput, and customer satisfaction are among the measures of effectiveness expected to be regularly monitored and tracked.
Whether a meter runs at rate 1 or 2, and just how much "red-time" a traveler will experience at any given meter during actual metered/operating hours, is based on a variety of factors programmed into custom software written for MnDOT's Traffic Management Centers computers. (see previous questions regarding metering rates and why ramp meters turn-on or stay in a flashing yellow mode). Generally, The actual red time for a specific ramp is based on the number of vehicles that use that ramp in a given hour. The higher the volume on the ramp the lower the red time used for the ramp.
During the course of this legislatively mandated study, it became clear that an all or nothing approach is not the best. Market research showed that 20 percent of commuters want the meters left off, roughly 10 percent of commuters want the ramp meters on as before, and about 70 percent want the ramp meters modified. (They want fewer meters, shorter operating hours and faster lights). The current modifications are a first cut at finding a balance between safety, system efficiency and public consensus. The impacts of these modifications will be monitored, and adjustments made as traffic patterns change and congestion levels continue to grow. For now, hours that the meters can come on are 6:30 to 8:30 in the morning and 3:30 to 5:30 in the evening.
Although the data has not yet been fully analyzed, certain trends were apparent, and each - along with other input received from a variety of sources and expertise from both in and outside of the Department - contributed to the ramp meter modifications. These trends included the fact that traffic operations improved in some places and degraded in others; accident rates appearing to be up (the impact on the severity of accidents is not yet known), and the majority of the public preferring a number of specific ramp metering modifications - including having ramp meters on for shorter periods of time during rush hours, less restrictive metering rates, and fewer meters turned back on.
These are longer-range policy questions that cannot be addressed until the results of the ramp meter shutdown study are completely analyzed and presented to the Legislature for its consideration.
The impacts of ramp meters on mass transit and other HOV's (like carpoolers) was one of the issues studied. Data regarding those impacts is presently still not available - but will be in time for the report to the legislatively mandated February 1, 2001 report. As part of its effort to balance both the engineering perspectives along with the needs of multiple system user groups like those who use transit or who carpool, the Agency will continue to track ramp meter modification impacts and make those adjustments which can technically and feasibly be made.
These are another set of longer-range policy questions that cannot be addressed until the results of the ramp meter shutdown study are completely analyzed and presented to the Legislature for its consideration.
The goals of MnDOT's metering system are to strike a balance between what is right and proper from an engineering perspective concerning the efficiency of moving as much traffic during the rush hours as possible, and the safety and other concerns of the people who use the system everyday. This goal is complicated by the dynamic and ever-shifting nature of traffic, and by the fact congestion is growing at an annual rate of 3.5 percent. What that means is that even with ramp metering, roadway congestion will continue to be a daily fact of life.