Ramp meter

A ramp meter is a device, usually a basic trafficlight , that regulates traffic entering freeways according to current trafficconditions. They have several aims. One is to break up platoons entering freeways, ensuring that traffic can merge easily. Asecond is to ensure that total flow on the freeway does not exceed capacity at downstream bottlenecks. Some metered ramps havebypass lanes for high occupancy vehicles , allowingcarpoolers 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 the USA

In the Los Angeles and Minneapolis-St. Paul metropolitan areas they are commonplace, andthey 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 theobjectives of safer and smoother merging onto the freeway traffic was easier without disrupting the mainline flows. Since thenramp-meters have been systematically deployed in many urban areas including Los Angeles, California , Minneapolis-St. Paul, Minnesota , Seattle, Washington , Denver, Colorado , Phoenix, Arizona , Portland, Oregon and Toronto, Ontario .Ramp meters have been withdrawn after initial introduction in several cities, including Austin, Texas , Dallas, Texas and San Antonio, Texas and Columbus, Ohio .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 .

In 2000 , an experiment was conducted involving shutting off all 433 ramp meters in theMinneapolis-St. Paul area for eight weeks to test their effects. In general ramp meters were shown to reduce accidents andmarginally 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 controlstrategies. Fewer meters are activated during the course of a normal day than what had happened prior to 2000, and timing hasbeen 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 bedynamic and only activate when the motorway reaches a certain level of congestion. When active, the system will only admit twovehicles ("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)