Ramp Metering in North America
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.
Ramp metering was first implemented in 1963 on the Eisenhower Expressway (Interstate 290) in Chicago by Adolf D. May, now a UC Berkeley professor. Since then ramp-meters have been systematically deployed in many urban areas including Los Angeles; San Diego; Sacramento; the San Francisco Bay Area; Fresno; Seattle; Denver; Phoenix; Las Vegas; Salt Lake City; Portland; Minneapolis-St. Paul; Milwaukee; Columbus; Cincinnati; Houston; Atlanta; Miami; Washington, DC (only along Interstate 395 and Interstate 66 in Arlington County, Virginia); Kansas City, Missouri; and along the Queen Elizabeth Way in Mississauga, Ontario, Canada.
Ramp meters are commonplace in the New York City, Los Angeles, San Francisco, Chicago, Seattle, Phoenix, Houston, Atlanta, Milwaukee, Columbus, and Minneapolis-St. Paul metropolitan areas, and they are also found in more than two dozen smaller metropolitan areas. In the New York City metro area, locals refer to ramp meters as "merge lights" and in Houston they're known as "flow signals."
Ramp meters have been withdrawn after initial introduction in several cities, including Dallas, San Antonio, and Austin, Texas. Disused metering signals can still be found along some parkways surrounding New York City and Detroit, as well as on one ramp to Interstate 64/U.S. Route 40 in St. Louis, MO, on the WB entrance ramp from McCausland Ave., which will be removed as part of the New I-64 project in winter 2008. Although deactivated shortly after they were added, ramp meters have been reactivated at select interchanges of Interstate 476 in suburban Philadelphia.
Ramp meters were installed along Interstate 435 in Overland Park, Kansas and Kansas City, Missouri in 2009, and are scheduled to go into effect on November 24, 2009.
Ramp meters in Mississauga, Ontario are designed in such a way so that if the queue waiting to enter the QEW grows to the point where it may back up onto city streets, the meter is lifted and all traffic entering the highway is able to move freely without waiting for the meter. The meter goes back into service once the ramp queue is reduced to a reasonable level. While this method may increase congestion on the highway itself, it has the benefit of keeping city arterials free of stopped traffic waiting in queue. Ramp queues are usually quite short, lasting only 5–6 seconds on average before the driver may continue to the freeway.
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