A
ramp meter,
ramp signal or
metering light is a device, usually a basic
traffic lightTraffic lights, also known as stop lights, stoplight, traffic lamps, stop-and-go lights, robots or semaphore, are signaling devices positioned at road intersections, pedestrian crossings, and other locations to control competing flows of traffic.Traffic lights have been installed in most cities...
or a two-section signal (red and green only, no yellow) light together with a signal controller, that regulates the flow of traffic entering
freewayA freeway is a type of road designed for safer high-speed operation of motor vehicles through the elimination of at-grade intersections. This is accomplished by preventing access to and from adjacent properties and eliminating all cross traffic through the use of grade separations and...
s according to current traffic conditions.
Ramp meters are claimed to reduce congestion (increase speed and volume) on freeways by reducing demand and by breaking up platoons of cars. Two variations of demand reduction are commonly cited; one being access rate, the other diversion.
Intended effect
Ramp meters are installed to
restrict the total flow entering the freeway, temporarily storing it on the ramps, a process called "access rate reduction." In this way, the traffic flow does not exceed the freeway's capacity. Another rationale for installing ramp meters is the argument that they
prevent congestion and break up "platoons" of cars. A platoon is a group of vehicles traveling in close proximity, such as a group released by an arterial traffic signal changing from red to green. Advocates of ramp meters claim that they break up platoons of vehicles entering freeways, ensuring that traffic can merge more easily. Another premise of ramp meters is
diversion. The delay caused by the ramp meter waiting period may cause some drivers to choose other routes thereby reducing demand for the freeway.
Types
Some metered ramps have bypass lanes for high-occupancy vehicles, allowing carpoolers and
busA bus is a road vehicle designed to carry passengers. A bus seats a maximum of 8 to 300 passengers...
es to skip the
queueQueue areas are places in which people in line wait for goods or services. Examples include checking out groceries or other goods that have been collected in a self service shop, in a shop without self service, at an ATM, at a ticket desk, a city bus, or in a taxi stand.Queueing is a phenomenon...
and get directly on the highway. Meters often only operate in
rush hourA rush hour or peak hour is a part of the day during which traffic congestion on roads and crowding on public transport is at its highest...
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.
Ramp metering signal controls
Ramp meter signals are set according to the current traffic conditions on the road. Detectors (generally an
induction loopInduction loop is a term used to describe an electromagnetic communication- and detection system, relying on the fact that a moving magnet will induce a electrical current in a nearby conducting wire. Induction loops are used for transmission and reception of communication signals, or for detection...
) 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 carriageway 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 are
ALINEAAlinea may refer to:• Alinea, a restaurant in Chicago by chef Grant Achatz
• Alinea, from the Latin a linea, referring to the pilcrow which indicates a new paragraph...
, demand control and fuzzy algorithms.
Demand control algorithms
The demand control algorithms are examples of
feed-forwardFeed-forward is a term describing an element or pathway within a control system which passes a controlling signal from a source in the control system's external environment, often a command signal from an external operator, to a load elsewhere in its external environment...
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.
Ramp metering in North America
This first application involved a
policeA police service is a public force empowered to enforce the law and provide security through the legitimized use of force.The term is most commonly associated with police services of a state that are authorized to exercise the police power of that state within a defined legal or territorial area of...
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 290Interstate 290 is a main Interstate freeway that runs westwards from the Chicago Loop. A portion of I-290 is officially called the Dwight D. Eisenhower Expressway. In short form, it is known as "the Ike" or the the Eisenhower...
) in
ChicagoChicago is the largest city in the U.S. state of Illinois, and with more than 2.8 million people, the 3rd largest city in the United States...
by Adolf D. May. Since then ramp-meters have been systematically deployed in many urban areas including
Los AngelesLos Angeles County is a county in California and is by far the most populous county in the United States. Figures from the U.S. Census Bureau give an estimated 2008 population of 9,862,049 residents, while the California State government's population bureau lists a January 1, 2009, estimate of...
;
San DiegoSan Diego , named after Saint Didacus , is the second-largest city in California and the ninth largest city in the United States, located along the Pacific Ocean on the west coast of the United States. The US Census Bureau estimates the city's population at 1,279,329 as of 2008...
;
SacramentoSacramento is the capital of the U.S. state of California, and the county seat of Sacramento County. Located along the Sacramento River and just south of the American River's confluence in California's expansive Central Valley. With a 2007 estimated population of 460,242, it is the seventh-largest...
; the
San Francisco Bay AreaThe San Francisco Bay Area, commonly known as the Bay Area, or the Yay Area, is a metropolitan region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses large cities such as San Francisco, Oakland, and San Jose, along with smaller urban and...
;
SeattleSeattle is located in the Pacific Northwest region of the United States. Situated in the western part of Washington State on an isthmus between Puget Sound and Lake Washington, about south of the Canada – United States border, it is named after Chief Sealth, of the Duwamish and Suquamish tribes...
;
DenverThe City and County of Denver is the capital and the most populous city of the state of Colorado, in the United States. Denver is a consolidated city-county located in the South Platte River Valley on the High Plains just east of the Front Range of the Rocky Mountains...
;
PhoenixPhoenix is the capital and largest city of the U.S. state of Arizona, as well as the fifth most populous city in the United States...
;
Las VegasThe Las Vegas metropolitan area, also known as the Las Vegas-Paradise-Henderson Metropolitan Statistical Area, is a metropolitan area in the southern part of the U.S. state of Nevada, consisting of Clark County. A central part of the metropolitan area is the Las Vegas Valley, a basin in which is...
;
Salt Lake CitySalt Lake City is the capital and the most populous city of the U.S. state of Utah. The name of the city is often shortened to Salt Lake or SLC. Salt Lake City has a population of 181,698 as of July 1, 2008, making it the 125th largest city in the United States...
;
Portland, OregonPortland is a city located in the Northwestern United States, near the confluence of the Willamette and Columbia rivers in the state of Oregon. As of July 2008, it has an estimated population of 575,930, making it the 29th most populous in the United States. It has been referred to as the most...
;
Minneapolis-St. PaulU.S. Census Bureau Areas|-! colspan="2" | |-! colspan="2" style="background:#d8d8e8;color:#000;" | Minneapolis-St. Paul-St. Cloud CSA, MN-WI
|-| Population || 3,502,891...
;
MilwaukeeMilwaukee is the largest city in Wisconsin and 23rd largest in the United States. It is the county seat of Milwaukee County and is located on the southwestern shore of Lake Michigan. Its estimated 2008 population was 604,477. Milwaukee is the main cultural and economic center of the...
;
Columbus, OhioColumbus is the capital and the largest city in the U.S. state of Ohio. It is the county seat of Franklin County, although parts of the city also extend into Delaware and Fairfield counties...
;
CincinnatiCincinnati is a city in the U.S. state of Ohio and the county seat of Hamilton County. The municipality is located north of the Ohio River at the Ohio-Kentucky border. The population within city limits was estimated to be 333,336 in 2008, making it the state's third largest city...
;
HoustonHouston is the fourth-largest city in the United States and the largest city within the state of Texas. As of the 2008 U.S. Census estimate, the city has a population of 2.2 million within an area of 600 square miles . Houston is the seat of Harris County and the economic center of...
;
AtlantaAtlanta is the capital and most populous city in the state of Georgia, as well as the urban core of one of the fastest-growing metropolitan areas in the United States....
;
MiamiMiami is a major coastal city in southeastern Florida, in the United States. Miami is the county seat of Miami-Dade County, the most populous county in Florida. With an estimated population of 424,662 in 2007, Miami is the largest city within the Miami metropolitan area, which is the...
; Washington, DC (only along
Interstate 395Interstate 395 in Virginia is a 13 mile long spur route that begins at a junction with Interstate 95 in Springfield, Virginia and ends in northwest Washington, D.C. It passes underneath the National Mall near the United States Capitol and ends at a junction with U.S...
and
Interstate 66Interstate 66 is an Interstate Highway in the eastern United States. As indicated by its even route number, it runs in an east-west direction. Its western terminus is at Middletown, Virginia, at an intersection with Interstate 81; its eastern terminus is in Washington, D.C., at an intersection...
in
Arlington County, VirginiaArlington County is a county of about 210,000 residents in the Commonwealth of Virginia. It is located directly across the Potomac River to the southwest of Washington, D.C. Formerly part of the District of Columbia, the land now composing the county was retroceded to Virginia on July 9, 1846, in...
); and the
Queen Elizabeth WayThe Queen Elizabeth Way is a 400-Series freeway in Ontario, Canada. It links Buffalo, New York, USA and the Niagara Peninsula with Toronto and its western suburbs. The freeway starts at the Peace Bridge in Fort Erie, Ontario and continues for 139 kilometres through Niagara Falls, St...
in
Mississauga, OntarioMississauga , incorporated in 1974, is a city in Southern Ontario located in the Regional Municipality of Peel, and part of the Greater Toronto Area. With a population of 668,549 as of the 2006 census, it is Canada's sixth-most populous municipality, and has almost doubled in population in each...
, Canada.
Ramp meters are commonplace in the
New York CityNew York is the most populous city in the United States, and the center of the New York metropolitan area, which is among the most populous urban areas in the world. A leading global city, New York exerts a powerful influence over worldwide commerce, finance, culture, fashion and entertainment...
,
Los AngelesLos Angeles is the largest city in the state of California and the second largest in the United States. Often abbreviated as L.A. and nicknamed The City of Angels, Los Angeles has an estimated population of 3.8 million and spans over in Southern California...
,
San FranciscoSan Francisco is the fourth most populous city in California and the 12th most populous city in the United States, with a 2008 estimated population of 808,976. It is the eighth most densely populated city in the U.S. and is the financial, cultural, and transportation center of the larger San...
,
ChicagoChicago is the largest city in the U.S. state of Illinois, and with more than 2.8 million people, the 3rd largest city in the United States...
, Seattle,
PhoenixPhoenix is the capital and largest city of the U.S. state of Arizona, as well as the fifth most populous city in the United States...
,
MilwaukeeMilwaukee is the largest city in Wisconsin and 23rd largest in the United States. It is the county seat of Milwaukee County and is located on the southwestern shore of Lake Michigan. Its estimated 2008 population was 604,477. Milwaukee is the main cultural and economic center of the...
,
ColumbusColumbus is the capital and the largest city in the U.S. state of Ohio. It is the county seat of Franklin County, although parts of the city also extend into Delaware and Fairfield counties...
, and
Minneapolis-St. PaulU.S. Census Bureau Areas|-! colspan="2" | |-! colspan="2" style="background:#d8d8e8;color:#000;" | Minneapolis-St. Paul-St. Cloud CSA, MN-WI
|-| Population || 3,502,891...
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."
Ramp meters have been withdrawn after initial introduction in several cities, including Dallas, San Antonio, and
Austin-Geographical locations:In the United States:*Austin, Texas, the state capital of Texas*Austin, Arkansas*Austin, Colorado*Austin, Chicago, in Illinois*Austin, Indiana*Austin, Minnesota*Austin, Nevada*Austin, Oregon...
, Texas. Disused metering signals can still be found along some parkways surrounding
New York CityNew York is the most populous city in the United States, and the center of the New York metropolitan area, which is among the most populous urban areas in the world. A leading global city, New York exerts a powerful influence over worldwide commerce, finance, culture, fashion and entertainment...
and
DetroitDetroit is the largest city in the U.S. state of Michigan and the seat of Wayne County. Detroit is a major port city on the Detroit River, in the Midwest region of the United States. Located north of Windsor, Ontario, Detroit is the only major U.S. city that looks south to Canada. It was founded...
, as well as on one ramp to
Interstate 64Interstate 64 is an Interstate Highway in the eastern United States. Its western terminus is at I-70, U.S. 40, and U.S. 61 in Wentzville, Missouri. Its eastern terminus is at an interchange with I-264 and I-664 at Bowers Hill in Chesapeake, Virginia. As I-64 is concurrent with U.S. 40 and U.S...
/
U.S. Route 40U.S. Route 40 is an east-west United States highway. As with most routes whose numbers end in a zero, U.S. 40 once traversed the entire United States. It is one of the original 1920s U.S. Highways, and its first termini were San Francisco, California, and Atlantic City, New Jersey...
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 476Interstate 476 is a auxiliary Interstate Highway in the U.S. state of Pennsylvania designated between Interstate 95 near Chester and Interstate 81 near Scranton, serving as the primary north-south Interstate corridor through eastern Pennsylvania...
in suburban Philadelphia.
Ramp meters in
Mississauga, OntarioMississauga , incorporated in 1974, is a city in Southern Ontario located in the Regional Municipality of Peel, and part of the Greater Toronto Area. With a population of 668,549 as of the 2006 census, it is Canada's sixth-most populous municipality, and has almost doubled in population in each...
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.
Minneapolis-Saint Paul ramp meter experiment
In 2000, a $650,000
experiment was mandated by the Minnesota State Legislature in response to citizen complaints and the efforts of State Senator Dick Day
http://www.senate.leg.state.mn.us/members/member_bio.php?district=26. 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 by
Cambridge Systematics and concluded that when the ramp meters were turned off freeway volume decreased by 9%, travel times increased by 22%, freeway speeds dropped by 7% and crashes increased by 26%. However, ramp meters remain controversial, and the
MinnesotaMinnesota is a state in the Midwestern region of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with 5.2 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the...
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.
Mainline metering
A
mainline 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 the San 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, the San Mateo Bridge and the
Dumbarton BridgeThe Dumbarton Bridge is the southernmost of the highway bridges that span the San Francisco Bay in California. Carrying over 81,000 vehicles daily, it is also the shortest bridge across San Francisco Bay at 1.63 miles...
. However, these mainline meters have not yet been activated (as of September 2006).
Beaverton, OregonBeaverton is a city in Washington County, Oregon, United States, seven miles west of Portland in the Tualatin River Valley., its population is estimated to be 86,205, almost 14% more than the 2000 census figure of 76,129...
has a mainline meter on the Cedar Hills Connector turning from Oregon Route 217 northbound to
U.S. Route 26U.S. Route 26 is an east-west United States highway. It started in Ogallala, Nebraska, and gradually grew to reach the West Coast in Oregon. When the U.S. highway system was first defined, it was limited to Nebraska and Wyoming; by the 1950s, it continued into Idaho and Oregon. The highway's...
eastbound. A mainline meter also exists on
California State Route 125State Route 125 currently runs from State Route 905 in Otay Mesa near the U.S.–Mexico border to State Route 52 in Santee.The southern portion of Route 125 from Route 905 to Route 54 near Chula Vista is a toll road called the South Bay Expressway. It is California's first road built as a...
southbound at its junction with Interstate 8 in
La Mesa, CaliforniaLa Mesa is a city in San Diego County, California, United States. The population was 54,749 at the 2000 census. It was founded in 1869 and officially incorporated as a city on February 16 1912...
.
Ramp metering in Europe
Ramp metering has been installed in several countries in Europe, including the United Kingdom, Germany and the Netherlands. A research project
Euramp on ramp metering funded by the European Union is due for completion in March 2007.
United Kingdom
Ramp metering is being introduced widely in the UK after a pilot study by the Highways Agency which concluded that ramp metering provides a net benefit under certain conditions - generally more congested junctions, but is ineffective or provides a net disbenefit under other conditions.
The Netherlands
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 the
AVV 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 runningRat running or cut-through driving refer to the use of secondary roads or residential side streets as opposed to the intended main roads in urban or suburban areas in order to avoid heavy traffic, lengthy traffic signals, or other obstacles lengthening a travel. Rat runs are frequently taken by...
'. By 2006 50 ramp meters were installed. This number increases by 4 to 5 each year.
Germany
Ramp metering has been implemented on
AutobahnsAutobahn is the German word for a major high-speed road restricted to motor vehicles capable of driving at least 60 km/h and having full control of access, similar to a motorway or freeway in English-speaking countries.In most countries, it usually refers to the German autobahn specifically...
in several areas in Germany, including the Ruhr area, Munich, and Hamburg.
Japan
Ramp metering is being installed in Japan in the next few years 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.
Australia
Ramp metering is used to regulate access to a number of major roads in
SydneySydney is the largest city in Australia, and the state capital of New South Wales. Sydney has a metropolitan area population of approximately 4.34 million and an area of approximately 12,000 square kilometres. Its inhabitants are called Sydneysiders, and Sydney is often called "the Harbour City"...
, including: M4 Western Motorway (Wallgrove Road on-ramp); the M5 East motorway (Kingsgrove Road on-ramp); and the citywest Link to Anzac Bridge. Ramp metering is also used on freeways in
MelbourneMelbourne is the capital city and most populous city of the State of Victoria, and the second most populous city in Australia. The Melbourne city centre is the anchor of the larger geographical area and statistical division known as the Greater Melbourne metropolitan area – of which Melbourne is...
, including the
Eastern FreewayThe Eastern Freeway is an urban freeway in eastern Melbourne, the state capital of Victoria, Australia. It is one of the most important freeways in terms of commuting to the city, connecting Alexandra Parade and Hoddle Street in the inner suburbs, with EastLink tollway farther east...
and the
Monash FreewayMonash Freeway is an urban freeway in Victoria, Australia linking Melbourne's CBD to its southeastern suburbs and the Gippsland region. The entire stretch of the Monash Freeway bears the designation...
. Brisbane's
Pacific MotorwayThe Pacific Motorway is a 100 km long motorway in Australia between Brisbane, Queensland, and the New South Wales-Queensland border at Tweed Heads. The motorway starts at Coronation Drive at Milton in Brisbane, and from 2008 links the Tweed Heads bypass in New South Wales. The Brisbane city section...
also uses Ramp metering on some on ramps. On most motorways, ramp metering is activated when sensors indicate that traffic is heavy, however, some motorways without sensors use time-based activation.
New Zealand
Ramp metering is being installed Auckland-wide after a successful trial on Mahunga Drive, before the
Mangere BridgeMangere Bridge, officially also called the Manukau Harbour Crossing, is a motorway bridge over the Manukau Harbour in south-western Auckland, New Zealand, crossing between the suburb also known as Mangere Bridge and the suburb of Onehunga...
. It is progressively being installed on 61 Southern, Northern and North Western Motorway on-ramps due to thick merging behaviour on several on-ramps during peak times. It will also be installed on all of the links. Auckland's ramp signals feature an amber light to clarify that normal traffic signal rules apply. Drivers failing to obey a red ramp signal will be ticketed and fined as if they had violated a normal red traffic light.
The majority of motorway on-ramps which did not already feature two-lane merging are being extended to allow for two lanes to the ramp signal stop line, to reduce on-ramp queue congestion (for example, Panmure on-ramp northbound). Where two lanes apply, one vehicle per lane is released per green signal. Due to their constrained design, other on-ramps remain one-lane only despite being ramp-signalled (eg Symonds Street on-ramp southbound).
Electronic message boards indicate whether ramp signals apply. The first board will display "RAMP SIGNAL ON" when ramp signals are activated, and the second board (closer to the on-ramp) "PREPARE TO STOP". Where ramp signals are switched off, the first board is blank and the second board displays "RAMP SIGNAL OFF".
Signals in Auckland have found a 30km/h average speed increase while Ramp Signals are running, and are allowing 600-650 more vehicles through motorway sections .
South Africa
Ramp meters have been installed on the Samrand South bound, Old Johannesburg South bound and on New Road North and South bound interchanges on the N1 Ben Schoeman highway. The ramp metering is part of the Intelligent Transport System launched in October 2007 to aid traffic flow between
JohannesburgJohannesburg also known as Jozi or Jo'burg, is the largest city in South Africa. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, having the largest economy of any metropolitan region in Sub-Saharan Africa...
and
PretoriaPretoria is a city located in the northern part of Gauteng Province, South Africa. It is one of the country's three capital cities, serving as the executive and de facto national capital; the others are Cape Town, the legislative capital, and Bloemfontein, the judicial capital.Pretoria is...
.
Has also been installed on the north bound on ramp from Blue Lagoon to the M4 Highway in Durban since early 2007
See also
- Ramp Meter Design Manual
External links