A one-way pair, one-way couple, or couplet refers to that portion of a bi-directional traffic facility – such as a road, bus, streetcar, or light rail line – where its opposing flows exist as two independent and roughly parallel facilities.
The one-way streets may be separated by just a single block, such as in a grid network, or may be spaced further apart with intermediate parallel roads.
One use of a one-way pair is to increase the vehicular capacity of a major route through a developed area such as a central business district.
If not carefully treated with other traffic calming features, the benefit in vehicular capacity is offset by a potential for increased road user deaths, in particular people walking and biking.
[1] A one-way pair can be created by converting segments of two-way streets into one-way streets, which allows lanes to be added without widening.It also allows easier creation of a green wave by adjusting traffic lights on the through route, because strict left turn phases are no longer required at each intersection.
[2] Flows on a one-way pair may follow the traffic handedness convention of the locale, or may be switched.
It was originally intended that the couplet system would serve as a stop gap measure prior to the construction of a freeway in Hobart's Transportation study of 1965.
Alberta Highway 2 is a one-way pair in southern Edmonton on Calgary Trail and Gateway Boulevard between 31 Avenue NW and Whitemud Drive.
British Columbia Highway 97 is a one-way pair through the community of Westbank in West Kelowna, following Main Street and Dobbin Road.
Both streets begin in Downtown near Point State Park before becoming a one-way pair just east of Market Square, with Forbes serving outbound traffic and Fifth serving inbound traffic, going through Uptown and Oakland before both streets end up with two-way traffic and diverge, with Fifth Avenue eventually terminating in Highland Park, while Forbes terminates in Wilkinsburg just outside the city limits.