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A frontage road (also access road, service road, parallel road, etc.) is a local road running parallel to a higher-speed, limited-access road. A frontage road is often used to provide access to private driveways, shops, houses, industries or farms. Where parallel high-speed roads are provided as part of a major highway, these are also known as local-express lanes.
Frontage roads provide access to homes and businesses which would be cut off by a limited-access road and connect these locations with roads which have direct access to the main roadway. Frontage roads give indirect access to abutting property along a freeway, either preventing the commercial disruption of an urban area that the freeway traverses or allowing commercial development of abutting property. At times, they add to the cost of building an expressway due to costs of land acquisition and the costs of paving and maintenance.
However, the benefits of development nearby real estate can more than offset the cost of building the frontage roads. Furthermore, a frontage road may be a part of an older highway, so the expense of building a frontage road may be slight. And finally, the cost to purchase access rights from adjacent property may exceed the costs to build frontage roads. Conversely, the existence of a frontage road can increase traffic on the main road and be a catalyst for development; hence there is sometimes an explicit decision made to not build a frontage road.
A backage road is a similar concept, but lies on the back side of the land parcels that abut the controlled access's right of way. Like the frontage road, it serves mainly to provide access to those parcels as an alternative to a frontage road.
There are several advantages to using frontage roads. One advantage is to separate local traffic from through traffic. When frontage roads are lacking in an urban area, the highway is used as a local road, reducing speeds and increasing congestion. Another advantage occurs when the highway is closed or just obstructed. This pushes traffic off the highway. Where an urban area has frontage roads, the traffic can easily bypass the obstruction or closure on the frontage road. Where an urban area has no frontage road, traffic congests local roads searching for that elusive passage around the obstruction or closure, since there is no formal (frontage road) alternative.
There are also some disadvantages to using frontage roads. When frontage roads are used without controlling the access to the main road, at every intersection an intersecting road runs from one side to another the number of conflict points increases one fold for each frontage road. This is because each frontage road is itself another intersection. Three examples are US 190 in East Baton Rouge Parish, Louisiana; LA 1 in West Baton Rouge Parish, Louisiana; and Palatine Road in Cook County, Illinois. Frontage roads also obviously take up large amounts of space and cost more. A highway with frontage roads is hard for pedestrians to cross, given the increased width of road, and vehicles in the central carriageways driving at high speeds.
The successor to the concept of service/frontage roads in urban freeways is the collector-express system, which is designed to handle closely spaced interchange ramps without disrupting through traffic. Unlike service roads, the collector lanes are typically high-speed full controlled-access lanes, conforming to freeway requirements.
The collector lanes may also be known as a collector/distributor road and slip ramps provide access to and from the express/mainline lanes. Frontage roads may feed into and from collector/distributor roads near some interchanges.
Ontario: A freeway with a significant remaining network of service roads is the Queen Elizabeth Way (QEW). However, most of the slip ramps between St. Catharines and Mississauga were removed during major reconstruction in the 1970s and 1990s. Service roads are no longer able to directly access the QEW; they have been rerouted to intersections with other major roads which have interchanges with the QEW. Nonetheless, the service roads are positioned too close to the QEW to easily widen the freeway unless all the private properties along the service road are bought out. This would be unlikely in the current political environment.
The only remaining slip ramps connecting to service roads are on the QEW running through St. Catharines. These dangerous low-standard ramps (due to lack of acceleration/deceleration lanes) are due to be replaced in a planned extensive reconstruction of the QEW that is currently underway. Similar service roads and slip ramps exist along Highway 401 through Oshawa, but like through St. Catharines, these are also in the process of being replaced with modern ramps.
Highway 427 had its service roads replaced with a collector-express system in the 1970s. However, it has several RIRO access onramps and offramps to serve residential traffic in addition to its standard parclo interchanges with major arterials.
List of Service Roads on the QEW:
List of Service Roads on the 403:
List of RIRO on the 427:
Quebec: Many autoroutes in the Montreal area (including the A-40, A-520, A-13, A-15 and A-25) maintain networks of frontage roads along at least some of their lengths as they pass through urban/developing areas.
In Guadalajara, the López Mateos, Vallarta and Mariano Otero avenues (the latter in the stretch between López Mateos to Niños Héroes) are 2-lane avenues surrounded by two one-way frontage roads. Lázaro Cárdenas Expressway is similar, but with three lanes in both the central road and the frontage roads. Because these frontage roads are considered as part of the avenue itself, the central road is known locally as the "central lanes", whereas the frontage roads are known as "lateral lanes". Turns are always forbidden in the central lanes; drivers wishing to make a turn must leave the central lanes and make the turn from the lateral lanes.
Frontage roads are common in the Netherlands and detailed in the Dutch national Design manual for bicycle traffic as per pages 121 and 127  where they are referred to as parallel roads. In the Netherlands, engineers have used frontage roads to benefit cyclists as well as automobiles. Because frontage roads only carry local traffic, the speed on these roads is low (their speed limit is 30 km/h), making them an ideal environment for bicyclists. Because the speed and volume is so low, no additional treatments are needed to make a service road a safe bike facility. In the Netherlands, service roads are often linked together with bike paths to help create a comprehensive bicycle route, with the bike path links serving as barriers to through motor traffic. Since service roads serve a dual purpose, they are an inexpensive way to create routes in cycling network, compared to cycletracks or stand-alone bike paths. Extensive amounts of information on frontage roads can be found on Northeastern's webpage.
In the People's Republic of China mainland, roads running next to expressways, taking outgoing traffic and feeding incoming traffic, are called either service roads or auxiliary roads (fudao locally). Where expressways cross larger urban areas, such frontage roads may run next to the expressway itself. Much of the Beijing portion of the Jingkai Expressway, for example, has, in fact, China National Highway 106 acting as a split-direction frontage road. Many newer urban highways are entirely elevated, with parallel access roads running beneath the entire length.
The South Luzon Expressway's Metro Manila Skyway and Pres. Sergio Osmeña Sr. Highway segments (both are apparently local and express roads) has two service roads and the PNR running alongside the road. The tracks are between the East Service Road and the highway, giving access to train stations from Pasay Road railway station to Bicutan railway station. The service roads begin at Sen. Gil Puyat Avenue up until the Filinvest exit.
Frontage roads exist both in city and along major expressways between new towns. Gloucester Road has frontage road running parallel of it from east to west. Cheung Tung Road serves as the frontage road for North Lantau Highway, Hiram's Highway for New Hiram's Highway, and Tai Wo Service Road West and Tai Wo Service Road East for Fanling Highway. Castle Peak Road serves the purpose as a frontage road of Tuen Mun Road to some extent.
In India, frontage roads or Service lanes (sometimes called नल्ला "Nullah" in Hindi) exist on most high density dual carriageway roads and dual carriageway highways. On Access controlled Expressways like the Yamuna Expressway, the frontage roads remain separate from the main carriageway throughout the road's length. Retrofitted and previously non-access controlled roads, such as most National Highways, only have service lanes on stretches where fly-overs (overpasses) are built over junctions or through towns.
Frontage roads are also common in Metro Detroit, where they are usually referred to as "service drives." As in Texas, they typically run one-way with frequent slip ramps to and from the limited-access roadway, with Texas U-turns at or near many intersections. Unlike Texas, there is usually little commercial development situated along the frontage road itself (see example); the road serves to provide access to the freeway from existing residential streets and commercial surface thoroughfares. Also unlike in many locales in urban Texas, where an exit ramp may actually precede the entrance ramp for the previous interchange to facilitate access to businesses situated directly on the frontage road (in effect, the two interchanges overlap along the frontage road), Michigan slip ramps to and from frontage roads are generally positioned as they normally would be in the absence of the frontage road. Motorists entering and exiting the freeway are not sharing the frontage road simultaneously to as large a degree, reducing weaving. Access to the frontage road between exits is provided by turnarounds and frequent bridging, generally every 1/2 mile, between exits.
Michigan left hand turns are also quite common at surface street-frontage road intersections, with dedicated turnaround lanes (similar to the Texas U-turn) built over the freeway on separate bridges approximately 100 meters from the main intersection and bridging.
With the exceptions of Interstate 275 and the freeway portion of M-53, every Metro Detroit freeway has a frontage road along it for at least a portion of its length. Several other freeways outside Metro Detroit use these as well.
There are no other Michigan frontage roads running more than one mile in length outside of the Metro Detroit area. New freeway construction in Michigan has not included frontage roads since the completion of Interstate 696, most of which was constructed along the rights of way of major surface arteries, in 1989.
One-way service roads on either sides of highways are relatively common in New York City. Due to the high urban density, this design allows rapid access on and off the highway while also providing a viable alternate route in the case of accidents and traffic. In the borough of Queens, the Van Wyck Expressway has this system implemented for most of its length. On Long Island, the Long Island Expressway (Interstate 495), has one-way service roads on each side of the expressway for most of its length from the Queens–Midtown Tunnel to Riverhead.
Most Texas freeways have service roads (feeder roads) on both sides. In urban and suburban areas, the traffic typically travels one-way, in the direction of the adjacent freeway. Most other areas have two-way traffic, but as an area urbanizes, the frontage road is often converted to one-way traffic (2 lanes). In cases of freeway congestion or shutdown, the frontage road provides an instant detour but delayed by each stop sign or stoplight at cross streets.
Over 80% of Houston freeways have service roads, which locals typically call feeders. Many service roads in urban and suburban areas of Texas have the convenience of Texas U-turns, as a left lane curving under an overpass, allowing drivers to avoid stopping for traffic lights when making a U-turn.
Service roads are often built as part of a multi-phase plan to construct new limited-access highways. They initially serve as a highway with access to local business before the freeway is constructed years later. After the completion of the freeway, frontage roads serve as a major thoroughfare for local activity, such as with the Katy Freeway project (I-10) in Greater Houston. In several cases, a long-range plan has called for a future freeway, but the design has either changed or the project was canceled before completion.
Nicknames for frontage roads vary within the state of Texas. In Houston and East Texas, they are called feeders. Dallas and Fort Worth area residents call their frontage roads "service roads", and "access roads" is the predominant term used in San Antonio. All signs reference "Frontage Road" despite local regional vernacular.
The free sections of Beltway 8 not part of the Sam Houston Tollway is composed of frontage roads.
In 2002, the Texas Department of Transportation proposed to discontinue building frontage roads on new freeways, citing studies that suggest frontage roads increase congestion. However, this proposal was widely ridiculed and criticized and was dropped later the same year.
The Stemmons Freeway in Dallas illustrates the practicability of the frontage road: the real estate developer John Stemmons offered free land to the Texas Highway commission in which to build a freeway (Interstate 35E) on the condition that the state build the freeway with frontage roads that would give access to undeveloped property that he owned along the freeway corridor. The state was able to reduce its costs (largely the cost of land acquisition) of building the freeway, and didn't need to acquire and demolish developed property; the developer profited from development along the freeway. San Antonio developer Charles Martin Wender used the same tactic for his Westover Hills development, offering free land through the middle of his property for SH 151 as well as paying half the costs for the initial frontage road construction. Following Wender's lead, several neighboring landowners also donated right-of-way for the route.
Frontage roads are common on interstate highways in North Carolina and South Carolina. Some of these road have houses facing the highways which they parallel. They may also have highway services, as most of them are located near interchanges. Most frontage roads in the Carolinas do not have ramps leading to and from their respective highways; rather, as mentioned before, most are located near interchanges, which allows people to exit the highway and go around to the frontage road if needed.