Permanently signed detour route
road classification and signage
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.
A permanently signed detour route should not be confused with a "permanent detour". The latter would be used if a particular roadway section, such as a bridge, were closed permanently.
Australia
New South Wales
The state of New South Wales in Australia has signposted detour routes, generally marked with the singular letter "D", on various motorways.
On the M1 Pacific Motorway between Newcastle and Sydney, both "D" and "D1" are used, to reduce ambiguity when two detour route sections meet each other.
The M5 East motorway has a permanently signed "D5" alternate route, used in the case of temporary road closures, and also by vehicles unsuitable for its tunnel. Unusually for detour routes, the D5 route is integrated into regular directional signage.
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