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Aramp meter,ramp signal, ormetering light is a device, usually a basictraffic light or a two-section signal light (red and green only, no yellow) together with a signal controller, that regulates the flow of traffic enteringfreeways according to current traffic conditions. Ramp meters are used at freeway on-ramps to manage the rate of automobiles entering the freeway. Ramp metering systems have proved to be successful in decreasingtraffic congestion and improving driver safety.
Ramp meters are claimed to reduce congestion (increase speed and volume) on freeways by reducing demand and by breaking up groups of cars. Two variations of demand reduction are commonly cited; one being access rate, the other diversion.[1] Some ramp meters are designed and programmed to operate only at times of peak travel demand; during off-peak times, such meters are either showing a steady green, flashing yellow (Maryland), or are turned off altogether. This allows traffic to merge onto the freeway without stopping. Other ramp meters are designed to operate continuously, only being turned off for maintenance or repairs.
Some metered ramps have bypass lanes forhigh-occupancy vehicles, allowing carpools, buses, and other eligible vehicles to skip thequeue and get directly on the highway. In other places such asNorthern California, carpool lanes are still metered, but the queue is typically shorter in comparison to regular lanes. Meters often only operate inrush hour periods. Some ramp meters have only one lane of traffic at the signal; others may have two or more lanes of traffic. Generally, meters with multiple lanes only give one lane the green light at a time. In one common configuration, each entrance lane has two signals; a red-yellow-green signal perched overhead over each lane (or mounted high on a pole for a single lane), and a two-phase lamp mounted low on a pole next to the stop line.
The overhead lights are for cars approaching the metering point; the low-mounted two-phase lights are intended to be used by the vehicle at the front of the queue. In normal operation of the ramp meters, only the red and green lamps are used. 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. (Once ramp metering is turned on, there is no further need for the yellow lamp.) In California, some meters allow two or three cars to proceed on a green light. 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.
In Ontario, the ramp meter lights are always green when there are no restrictions in place for traffic to proceed.[2]
The sophistication and extent of a ramp metering system is based on the amount of improvement desired, existing traffic conditions, installation costs, and the continuing resource requirements that are necessary to operate and maintain the system effectively. The simplest form of control is a fixed time operation. It performs the basic functions of breaking upplatoons into single-vehicle entries and setting an upper limit on the flow rates that enter the freeway. Presence and passage detectors may be installed on the ramp to actuate and terminate the metering cycles, but the metering rate is based on average traffic conditions at a particular ramp at a particular time. 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. Pre-timed control can be implemented on any number of ramps, and is often implemented as an initial operating strategy until individual ramps can be incorporated into a traffic responsive system.
The next level of control, traffic responsive, establishes metering rates based on actual freeway conditions. The local traffic responsive approach utilizes detectors and a micro-processor to determine the mainline flow in the immediate vicinity of the ramp and the ramp demand to select an appropriate metering rate. Traffic responsive control also permits ramp metering to be used to help manage demand when incidents occur on the freeway, i.e. reduce the metering rate at ramps upstream of the incident and increase the rate at ramps downstream.
System-wide control is a form of traffic responsive control but operates on the basis of total freeway conditions. Centralized computer controlled systems can handle numerous ramps in a traffic responsive scheme and feature multiple control programs and overrides. Control strategies can also be distributed among individual ramps. A significant feature of system control is interconnection that permits the metering rate at any ramp to be influenced by conditions at other locations. Denver showed that this type of control has significant benefits when properly applied.
System control need not be limited to the freeway and its ramps. The concept of integrated traffic control combines or coordinates freeway and arterial street control systems to operate on the basis of corridor wide traffic conditions. The potential advantages of integrated control include reduced installation and operating costs, corridor wide surveillance, better motorist information, and quicker and coordinated use of all of the control elements (meters, signals, signs, etc.) in response to real time traffic conditions. Simulation results from one study showed that, during an incident, coordination of arterial traffic signals and ramp meters can improve the traffic performance of a corridor.
Ramp meter signals are set according to the current traffic conditions on the road. Detectors (generally aninduction loop) are installed in the road, both on the ramp and on the main road which measure and calculate the traffic flow, speed and occupancy levels. These are then used to alter the number of vehicles that can leave the ramp. 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.
Much research is currently being carried out into the most appropriate algorithms for controlling ramp meter signals. Some algorithms that are in use or have been evaluated areALINEA, demand control and fuzzy algorithms.
The demand control algorithms are examples offeed-forward control. One version of the demand control algorithm is the RWS strategy used in the Netherlands. In this algorithm the number of vehicles that the signals allow off the ramp is calculated as the difference between the flow before the ramp and the pre-specified capacity of the road.
This first application involved apolice 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) inChicago by Adolf D. May, now a UC Berkeley professor.[3] Development insystems control theory allowed for improved traffic regulation throughout the early 1970s, pioneered by Leif Isaksen in his paper "Suboptimal Control of Large Scale Systems with Application to Freeway Traffic Regulation."[4] Since then ramp-meters have been systematically deployed in many urban areas includingLos Angeles;San Diego;Sacramento; theSan 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 alongInterstate 270 inMontgomery County, Maryland andInterstate 395 andInterstate 66 inArlington County, Virginia);Kansas City, Missouri;[7] and along theQueen Elizabeth Way inMississauga, 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 theU.S. Environmental Protection Agency, which was looking for innovative ways to reduce air pollution in California by make the transportation system more effective.[8]
Ramp meters are commonplace in theNew York City,Los Angeles,San Francisco,Chicago,Seattle,Phoenix,Houston,Atlanta,Milwaukee,Columbus,[9] andMinneapolis-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, includingDallas,San Antonio, andAustin, Texas. Disused metering signals can still be found along some parkways surroundingNew York City andDetroit. Although deactivated shortly after they were added, ramp meters have been reactivated at select interchanges ofInterstate 476 in suburbanPhiladelphia.
Ramp meters were installed alongInterstate 435 inOverland Park, Kansas andKansas City, Missouri in 2009.[7] In 2017, ramp meters were installed alongInterstate 35 in Kansas City.[10]
Ramp meters inMississauga, Ontario are designed in such a way so that if the queue waiting to enter theQEW 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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In 2000, a $650,000 experiment was mandated by the Minnesota State Legislature in response to citizen complaints and the efforts of State SenatorDick Day. The study involved shutting off all 433 ramp meters in the Minneapolis-St. Paul area for eight weeks to test their effectiveness. The study was conducted byCambridge Systematics and concluded that when the ramp meters were turned off freeway capacity decreased by 9%, travel times increased by 22%, freeway speeds dropped by 7% and crashes increased by 26%.[11] However, ramp meters remain controversial, and theMinnesota State Department of Transportation has developed new ramp control strategies. Fewer meters are activated during the course of a normal day than prior to the 2000 study, some meters have been removed, timing has been altered so that no driver waits more than four minutes in ramp queue, and vehicles are not allowed to back up onto city streets.
Amainline meter throttles traffic flow from one segment of a highway to the next by directly metering the highway's traffic. Such a scheme is typically implemented in specialized situations such as bridges and tunnels. A mainline meter was installed at theSan Francisco–Oakland Bay Bridge toll plaza in the early 1970s. Similar mainline meters have also been installed downstream from the toll plazas at two other San Francisco Bay crossings, theSan Mateo Bridge and theDumbarton Bridge. However, these mainline meters have not yet been activated (as of September 2006).[needs update] A mainline meter also exists onCalifornia State Route 125 southbound at its junction withInterstate 8 inLa Mesa, California.
Ramp metering has been installed in several countries in Europe, including the United Kingdom, Germany and the Netherlands. A research project,EURAMP - European Ramp Metering Project, funded by the European Union was completed in March 2007. The EURAMP Project Deliverables[12] included information about the results of ramp metering in a number of locations and situations, and whether they were helpful in those situations, and aHandbook of ramp metering.
The first trial in the UK was on the M6 J10 near Walsall in 1986. 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[13] 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. In its conclusion it "envisaged ramp metering will be deployed more widely in the coming period." 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[14] on the 4,500 miles (7,242 km) of strategic highways operated and maintained by the HA.
The first ramp metering in the Netherlands was introduced in 1989. Ramp metering is being introduced more widely in the Netherlands after a pilot study by theAVV Transport Research Centre which concluded that ramp metering can provide a small benefit for the traffic flow on the highway, leading to a higher capacity. Ramp meters can also contribute to decreasing 'rat running'. By 2006 50 ramp meters were installed. This number increases by 4 to 5 each year.
Ramp metering has been implemented onAutobahns in several areas in Germany, including the Rhine-Ruhr area, Munich, and Hamburg.
Ramp metering has been implemented onTangenziale di Venezia (A57) as temporary solution for the increased traffic before the definitive solution (building of thePassante di Mestre).
There is one metered ramp in Ireland, located at J1 on theM1 Motorway (Ireland) Northbound. It is on the entry ramp from Coolock Lane, and is used when the M1 gets congested due to the M1 Port Tunnel and the M1 meeting further up.[15]
The first two ramp meters in the country were installed in 2022 on two on-ramps onexpressway S2 in Warsaw. These are the last on-ramps before the entrance ofthe Ursynów Tunnel both eastbound and westbound.[citation needed]
Ramp metering is being installed in Japan in the next few years[when?] to keep the flow of traffic moving in Japan. There are plans to install ramp meters on every on-ramp in the Japan motorway system.[citation needed]
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The largest ramp metering network in the country is inMelbourne (managed and controlled throughVicRoads) on theEastern Freeway and most of all, on the entire inner-city M1 route which includes theMonash Freeway, theCityLinkTollway, theWest Gate Freeway and the metropolitan section (south of the beginning of theMonash Freeway) for thePrinces Freeway. There are also various ramp meters on the inner-city section of theCalder Freeway.Brisbane'sPacific Motorway andBruce Highway (S/Bound Caboolture - Gateway Mwy) also uses ramp metering on some on-ramps, as does the northbound on-ramps ofPerth'sKwinana Freeway betweenRoe andCanning Highways. On most motorways, ramp metering is activated when sensors indicate that traffic is heavy, however, some motorways without sensors use time-based activation.
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 theTechnical University of Crete. The system was built on theSTREAMS platform and utilises the state-of-the-art ITS architecture. All the ramps can be linked when required to resolve motorway bottlenecks before they emerge. 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. The HERO system takes real time data every 20 seconds from the motorway, ramps and arterial road in order determine the best signal timing for the next 20 seconds. The data detection system comprises Sensys detectors in every freeway lane at 500 m (1,640 feet ) spacings with a minimum detectors at three locations on each ramp including the freeway entrance with the arterial road. The system also manages the arterial road interface with the freeway, balances ramp queues and delays across ramps, and is capable of managing bottlenecks 3–4 km (1.8 - 2.4 mi) downstream of a ramp entrance. The system is also supplemented by real-time travel-time information to key destinations and incident and congestion information displayed on specially designed full-colour VMS on the approaches to the freeway entrance ramps. This information provides sufficient advice for motorists to determine whether or not to use the freeway during incidents etc. The system also provides dynamic ramp closure in the event of a major incident.
Ramp metering was introduced on the Rozelle Interchange in Sydney in 2024 to alleviate congestion for Victoria Rd users, after lengthy delays and back-ups through Drummoyne and Rozelle and onto the Anzac Bridge.[16]
Auckland has currently 91 ramp meters across the Southern, South Western, Northern and North Western motorways making it the largestSouthern Hemisphere ramp metering system.[17] Ramp metering was installed Auckland-wide after a successful trial on Mahunga Drive in 2004,[18] before theMangere Bridge.
Traffic data collected from 25 ramp metering sites in 2007 (before ramp metering deployment) and 2009 (after) shows an average 25% improvement in both congestion duration and traffic speed as well as an 8% increase in traffic throughput. The data also shows an average reduction in crashes of 22%.[17] This performance and safety data translates into estimated benefits of US$1.6M per ramp metering site per year.
The system controlling the ramps promotes the traditional coordination among on-ramps as well as real-time integration with traffic signals on the adjacent arterial network allowing the whole road network to be managed as a single integrated network.[19] For example, when motorway incidents adversely impact the adjacent arterial roads, an automatic response to the arterial traffic signals can be triggered to mitigate the impacts of the incident and vice versa. 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 adaptiveSCATS system controls both arterial traffic lights and motorway ramp meters.
The termRamp Signalling[20] rather thanRamp Metering is purposefully adopted in New Zealand as a user-oriented name.
Ramp meters were, for a while, installed on the Samrand South bound, Old Johannesburg South bound and on New Road North and South bound interchanges on the N1Ben Schoeman highway. The ramp metering was part of the Intelligent Transport System launched in October 2007 to aid traffic flow betweenJohannesburg andPretoria.
A ramp meter has also been installed on the northbound on-ramp from Blue Lagoon to the M4 Highway in Durban since early 2007.
Freeways in Taiwan use ramp meters during peak hours since 1993.[21]Traffic enforcement cameras are deployed to deter running the red lights, but abus lane at Taipei Interchange from northbound Chongqing North Road to southboundNational Highway No. 1 in northernDatong District, Taipei allows buses and properly indicated emergency vehicles to bypass the traffic control imposed by the ramp meters.[22]
In 2016, two ramp meters were installed on a major highway inIstanbul.[23] It has been noted that there is a 10% improvement in traffic provement along with 20% decrease in delays.[citation needed]
On some ramp meters, there is a singular red light on the backside of the signal that is synchronized with the red light on the traffic signal that the drivers see when queueing. When the queueing drivers see the red light on the traffic signal, the backside red light is on, when the traffic signal displays green or yellow, the backside red light is off. This allowshighway patrol to enforce the metering lights by having anofficer park theircar ormotorcycle on theshoulder a short distance past the targeted signal, watch the red light for any offenders, and pull them over. Additionally, if the given ramp has a carpool bypass lane, officers from that vantage point may also catch and pull over non-carpoolers who are illegally using the carpool lane to skip past the ramp meter queue.On westboundI-80 inOakland, California just past theBay Bridge toll plaza, there is a section with overhead metering lights that cycle when the freeway traffic volumes are high, equipped withcameras that capture license plate images of drivers who run the red light and then send a fine.
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