Ramp meter
Ramp metering systems have proved to be successful in decreasing traffic congestion and improving driver safety.
However, when ramp metering is about to be enabled, the overhead lamps may show flashing or solid yellow to warn drivers to prepare to stop.
These meters use red-yellow-green signals on both the upper and lower mounts on the pole, and operate in a standard green-yellow-red fashion.
It performs the basic functions of breaking up platoons into single-vehicle entries and setting an upper limit on the flow rates that enter the freeway.
This type of operation provides the benefits associated with accident reductions, but is not as effective in regulating freeway volumes because there is no input about mainline traffic.
The next level of control, traffic responsive, establishes metering rates based on actual freeway conditions.
A significant feature of system control is interconnection that permits the metering rate at any ramp to be influenced by conditions at other locations.
The more congested the main freeway, the fewer vehicles are allowed to leave the ramp, this is effected by giving longer red times to the traffic signals.
Ramp metering was first implemented in 1963 on the Eisenhower Expressway (Interstate 290) in Chicago by Adolf D. May, now a UC Berkeley professor.
"[4] Since then ramp-meters have been systematically deployed in many urban areas including Los Angeles; San Diego; Sacramento; the San Francisco Bay Area; Fresno; Philadelphia, Pennsylvania; Seattle; Spokane;[5] Denver; Phoenix; Las Vegas; Salt Lake City; Portland, Oregon; Minneapolis-St. Paul; Milwaukee; Columbus; Cincinnati;[6] Houston; Atlanta; Miami; Orlando; Washington, DC (only along Interstate 270 in Montgomery County, Maryland and Interstate 395 and Interstate 66 in Arlington County, Virginia); Kansas City, Missouri;[7] and along the Queen Elizabeth Way in Mississauga, Ontario (Toronto-bound ramps from Cawthra Road, Hurontario Street, Mississauga Road, Erin Mills Parkway, Winston Churchill Boulevard, Ford Drive) Canada since the 1970s.
[2] In the early 1970s, this traffic control practice drew the attention of the U.S. Environmental Protection Agency, which was looking for innovative ways to reduce air pollution in California by make the transportation system more effective.
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Ramp meters have been withdrawn after initial introduction in several cities, including Dallas, San Antonio, and Austin, Texas.
Although deactivated shortly after they were added, ramp meters have been reactivated at select interchanges of Interstate 476 in suburban Philadelphia.
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.
No more sites were developed for the next two decades until a second 'pilot' study in 2006 by the Highways Agency (HA) concluded that ramp metering provides a net benefit under certain conditions - generally more congested junctions.
A Summary Report[12] by the HA, dated November 2007, includes an overview of the background and history, international experience, limitations, system operation, algorithms and implementation of ramp metering.
Ramp metering was then introduced widely in England - Phase 1 involved the implementation of approximately 30 sites and was completed by 2008.
Phase 2 followed and as of March 2011 there are 88 Ramp Metering sites[13] on the 4,500 miles (7,242 km) of strategic highways operated and maintained by the HA.
The 2010 M1 Upgrade in Melbourne installed 62 ramp meters that are coordinated using the HERO suite of algorithms developed by Markos Papageorgiou and Associates from the Technical University of Crete.
The results of a trial improved capacity by 9% over the previous fixed-time ramp-metering system, average speeds increased by 20 km/h (12 MPH) and traffic throughput at bottleneck locations can be reliably maintained around 2200 PCE per lane.
Recurrent and excessive traffic queues at on-ramp and off-ramp can also be managed in an integrated way in real-time.
This integrated management is possible in Auckland because the same adaptive SCATS system controls both arterial traffic lights and motorway ramp meters.
The ramp metering was part of the Intelligent Transport System launched in October 2007 to aid traffic flow between Johannesburg and Pretoria.
[19] Traffic enforcement cameras are deployed to deter running the red lights, but a bus lane at Taipei Interchange from northbound Chongqing North Road to southbound National Highway No.
1 in northern Datong District, Taipei allows buses and properly indicated emergency vehicles to bypass the traffic control imposed by the ramp meters.
On westbound I-80 in Oakland, California just past the Bay Bridge toll plaza, there is a section with overhead metering lights that cycle when the freeway traffic volumes are high, equipped with cameras that capture license plate images of drivers who run the red light and then send a fine.
