Ramp meter
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A ramp meter or metering light is a device, usually a basic traffic light, that regulates traffic entering freeways according to current traffic conditions. They are intended to reduce congestion on the freeway in two ways. One is to break up platoons of vehicles entering freeways, ensuring that traffic can merge more easily. A second is to ensure that total flow on the freeway does not exceed capacity at downstream bottlenecks. Some metered ramps have bypass lanes for high occupancy vehicles, allowing carpoolers and vehicles like buses to skip the queue and get directly on the highway. Meters often only operate in rush hour periods.
Ramp metering in North America
In the Los Angeles and Minneapolis-St. Paul metropolitan areas they are commonplace, and they are found in more than two dozen smaller metropolitan areas.
Ramp metering was first implemented in 1963 on the Eisenhower Expressway (Interstate 290) in Chicago, Illinois. This first application involved a police officer who would stop traffic on an entrance ramp and release vehicles one at a time at a predetermined rate, so that the objectives of safer and smoother merging onto the freeway traffic was easier without disrupting the mainline flows. Since then ramp-meters have been systematically deployed in many urban areas including Los Angeles, California, Minneapolis-St. Paul, Minnesota, Seattle, Washington, Denver, Colorado, Phoenix, Arizona, Salt Lake City, Utah, Portland, Oregon, and Toronto, Ontario. Ramp meters have been withdrawn after initial introduction in several cities, including Austin, Texas, Dallas, Texas, and San Antonio, Texas and Columbus, Ohio. Disused metering signals can still be found, forgotten along some parkways surrounding New York, New York and Detroit, Michigan.
In 2000, an experiment (http://www.dot.state.mn.us/rampmeterstudy/) was conducted involving shutting off all 433 ramp meters in the Minneapolis-St. Paul area for eight weeks to test their effects. In general, ramp meters were shown to reduce accidents and marginally reduce total travel time compared with the unmetered case. However, they remained controversial, and the Minnesota state Department of Transportation has developed new, less onerous ramp control strategies. Fewer meters are activated during the course of a normal day than what had happened prior to 2000, and timing has been altered.
Ramp metering in Australia
Ramp metering will first be used on February 9, 2004, at the Kingsgrove Road on ramp to the M5 East motorway in Sydney, which has been introduced by the Roads and Traffic Authority (RTA) in the "Merge Safe" initiative. Ramp metering here will be dynamic and only activate when the motorway reaches a certain level of congestion. When active, the system will only admit two vehicles ("one vehicle per green, each lane").
Ramp metering is also used on the Western Motorway (the M4), at the intersection of Wallgrove Road and the motorway.
External links
- M5 Merge Safe (RTA) (http://www.rta.nsw.gov.au/trafficinformation/m5_mergesafe.html)