Twin Cities Metro Area Ramp Meter Study FAQs
Nov. 2001 FAQs
A new ramp meter control system will be phased in over the next year to all existing meters. The new system implements several lessons learned since the official Ramp Meter Study was conducted in Fall of 2000. The new system will be implemented in stages as work is completed on installing queue detectors on the ramps. About 30 percent of ramps currently have queue detectors. These ramps are on the following corridors: I-35W, I-35E, I-494, I-94, Highway 100, Highway 169, Highway 62 and Highway 77. These corridors will be the first to implement the new ramp meter system. Approximately 160 queue detectors will be installed on remaining ramps in 2002 and will allow complete deployment of the new system.
The primary goals of the new ramp metering system are 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.
These goals will be measured by the following performance standards:
- Ramp meter waits will be no more than four minutes per vehicle on local ramps and two minutes per vehicle on freeway-to-freeway ramps.
- Vehicles waiting at meters will not back up onto adjacent roadways.
- Meter operation will respond to congestion and operate only when needed.
That ramp meter study is complete. The new system design is the result of lessons learned and is expected to be a long-term solution. MN/DOT will continue to monitor all ramp meters and will make modifications as traffic patterns change.
Ramp meter rates will be determined by two main factors: 1) Congestion conditions on the mainline freeway and 2) Real-time traffic levels on the metered ramp. The ramp meter will react to freeway congestion conditions up to three miles from the ramp. Queue detectors have been installed on ramps to help determine queue lengths and prevent unacceptable waits. Meter timing will be adjusted every 30 seconds.
The ramp meter study is now concluded. MnDOT will continue to study the performance of the ramp meter system and make changes to timing as traffic conditions change.
The decision was based on the market research and traffic data analysis conducted under contract with Cambridge Systematics.
There are 233 meters that operate in the morning peak period and 283 meters that operate in the afternoon peak period. The new system will initially be deployed on about 30 percent of these meters. The remaining meters will operate as they currently do until queue detectors can be installed on the entrance ramps.
Ramp meters are generally only run during morning and evening peak periods. Occasionally, a ramp meter may be turned on at other times to aid in traffic control for incidents or maintenance activities.
Cambridge Systematics, the independent consultant who oversaw the ramp meter studies, conducted random telephone surveys of 500 commuters in the Twin Cities metropolitan area in September 2001. The purpose of the surveys was to assess the public's perception of the interim ramp metering system implemented in December 2000, following completion of the shutdown experiment. The survey design and sampling plans were similar to that used to gauge public reaction to the old ramp metering system in September/October 2000 and to the ramp meter shutdown experiment in October/November 2000. The major difference was that previously a random survey of 250 commuters and four corridor-specific surveys of 125 commuters each were completed. During this recent market research period, a single random survey of 500 commuters was conducted instead. There were no significant differences in the findings of the earlier random survey versus the corridor-specific surveys.
Transit riders and car-poolers will save time by using HOV bypasses at ramps that have queues. Additionally, MnDOT will continue to consider installing new HOV bypasses on a case by case basis.
During the study questions and comments were submitted via an online form.
Twenty-four meters scattered throughout the metro area have been targeted for removal in 2002. This group is comprised of meters that currently are not used. Because their operation would not help meet the new system goals, there is no need to use these meters in the next five years. Additional meters may be removed if sufficient capacity improvements are made or corridors cannot be effectively managed with meters.
Installation of new meters will be considered only where reoccurring congestion exists and it can be assured that ramp metering would have a positive influence on the corridor's operation.
Queue detectors installed in September of 2001 had an average cost of $3500 per entrance ramp. It is estimated that a total of 200 ramps will have new detection installed in 2002 with an approximate final cost of $700,000.
There are two basic metering control strategies. One is "local control" in which a ramp meter operates based on conditions only on the ramp and the mainline point adjacent to the meter. Variations of this strategy are in place in Chicago and Toronto. The second strategy is called "central control." In central control ramp meters and traffic detectors communicate with a central computer, typically located at a Traffic Management Center. The central computer processes all of the information and tries to coordinate timing among several ramp meters in predefined corridors. Several cities have centrally controlled systems including Seattle, Denver, San Diego and the Twin Cities. Each city, though, has their own strategies and goals for operation. Denver and Seattle are examples of cities that incorporate information from queue detectors into the ramp meter timing.
The new metering system will use a combination of existing and new queue loops. Queue loops have not been a part of previous metering strategies because they were not needed to meet the system goals. The existing queue detectors where originally installed for use in generating traveler information about ramp queue wait time. Information from the existing queue loops will not be incorporated into the new ramp metering system.
MN/DOT estimates the removal of meters will cost between $500 and $1000 per entrance ramp. Of the 24 meters being removed, 12 were operational prior to the ramp meter study. None of the 24 meters have been operational since the initial ramp meter shutdown in October 2000.
MnDOT is confident that motorists will obey the ramp meter and HOV laws. It is a moving violation to run a red light at a ramp meter and for single occupant vehicles to use the HOV bypass ramps. MnDOT will work with the State Patrol if problems develop. As in the past, MnDOT will forward any motorists observations about ramps with high violation rates to the State Patrol.
MnDOT will continue to monitor system performance on a daily basis. Monitoring includes performing routine analysis of system information to ensure that the ramp meter goals are being met, and performing responsive analysis whenever problems are reported. Changes to timing will be made as necessary. The new system will automatically adjust timing in response to any changes in traffic patterns or because of malfunctioning field equipment. The system analysis is performed using information provided by field detectors and through field observations by MnDOT staff. MnDOT will also capture public opinion about system performance through a variety of market research efforts that are performed on a yearly basis.