Permanently signed detour route
A permanently signed detour route (also known as an emergency detour route or emergency diversion route) is a type of route which is used temporarily during special circumstances. Various areas have developed these systems as part of incident management. The purpose of these routes is to provide a detour in the event that the parent route is impassable, due to either a traffic jams, traffic collision, or road closure (for a variety of reasons). Sometimes these routes are signed as a prefixed or suffixed numbered road, making them a type of special route.
The province of Ontario in Canada is one jurisdiction outside the United States with a very prevalent system of these roads. The Emergency Detour Routes, originally Emergency Diversion Routes (EDR), are a system of temporary detour routes paralleling many major highways in Ontario. Most of these follow county or municipal roads within the province that are not (currently) provincially controlled (though many were former provincial highways). These routes are designed to be used in the event of a closure on a major road or 400-series highway, such as construction or serious collisions.
Though most EDRs are set up along 400-series highways, a select few have been established along two lane King's Highways, notably Highway 21 due to the lake effect of Lake Huron, which can result in sudden snowsquall conditions during the winter.
Halton was the first jurisdiction in Ontario to create EDRs, although it initially referred to them as Emergency Diversion Routes. In August 1999, the regional council approved the preparation of the Road Closure Action Plan (RCAP), which was developed with input from the Halton Regional Police Services and the Ministry of Transportation of Ontario (MTO). The RCAP utilized folding signs that police could open to "activate" the route. Similar in appearance to the EDR signs of today, the RCAP signs featured a trapezoid shaped orange EDR sign, as opposed to an orange square with a black circle containing the letters EDR. These signs were first deployed along a limited stretch of the Queen Elizabeth Way in March 2001, between Dorval Drive and Trafalgar Road in Oakville and between Bronte Road and Burloak Drive in Burlington, both the location of major ravines with limited alternative crossings.
By the spring of 2003, when the deployment of the system was complete, the entire Queen Elizabeth Way, Highway 401 and Highway 403 had diversion routes within Halton Region. Following Halton's tests, the MTO and the Ontario Good Roads Association formed a joint task force, and using the RCAP as a model, developed the Emergency Detour Route program.
Sweden use signs with white background and blue text for their permanent detour routes (Swedish: permanent omledningsväg) on numbered roads. According to the Swedish Transport Administration's guidelines a permanent detour route should be able to handle all the traffic when it comes to capacity, weight, height, etc. as sorting traffic is almost impossible. In cases that for some reason need traffic sorting the police will regulate the traffic. However, there may be different routes for different travel directions as to not create accessibility problems or queues due to limited capacity; in these cases a letter for the cardinal direction is added at the end. The guidelines also emphasize that the segments of the permanent detour route should be as short as possible with access to the main route whenever it is possible.
United Kingdom and Ireland
The United Kingdom and the Republic of Ireland use yellow signs with a series of symbols for their emergency diversion routes. Symbols come in a shapes, with a solid and hollow version, including circle, triangle, square and diamond. When a roadway is closed, a trigger sign is opened at the last junction prior to the closure, displaying a symbol, which motorists can follow to rejoin the route at a point beyond the closure.
The national MUTCD has not yet adopted standard signage for these routes. Some states have adopted their own systems.
Michigan has a system of special routes called "Emergency" routes which parallel major highways, primarily in Southwestern Michigan. These routes provide relief in the event of emergency closures to a freeway due to accidents, weather, or other civil emergencies. Emergency routes have been gradually put in place as part of a broader plan by the Michigan Department of Transportation (MDOT) to upgrade its ITS network across the state. These detours may or may not follow MDOT-maintained State Highways, however, and some portions of the routes pass through urban or suburban areas. Emergency routes exist on and parallel to Interstate 69 (I-69) and I-94 and US Highway 31 (US 31).
These routes are signed with an auxiliary "Emergency" plate that is colored orange, indicating a temporary traffic control sign.
Emergency US 31, which offers an alternative crossing of the Grand River in the event that the bascule bridge in Grand Haven, Michigan is unavailable for motorists, is one such route. According to MDOT, "this route would only be used in emergency situations and worst-case scenarios impacting the entire bridge structure."
Missouri uses "Incident By-Pass Routes" along its highways.
The New York State Thruway uses emergency detour signs to divert traffic from the Thruway in the event of weather conditions or other emergencies.
Alternate Interstate routes also exist for I-70 near Dayton as well as for Interstate 76 and Interstate 77 in Summit County.
Pennsylvania has a system of "color detour signs" in which any detour follows signs with a specific color. The detours are meant to be used if a limited-access highway has to be closed for an emergency situation such as a flood or car accident, directing motorists along local roads near the limited-access highway to the next exit. They are generally color-coded according to direction, with blue meaning north, red meaning south, green meaning east, and orange meaning west. However, other colors are sometimes used when detour routes overlap with one another.
Wisconsin has "alternate route designations" in various areas of the state.
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