One-way pair

A one-way pair, one-way couple, or just couplet is a pair of parallel, usually one-way streets that carry opposite directions of a signed route or major traffic flow, or sometimes opposite directions of a bus or streetcar route. They are controversial due to their higher rates of crashes, increased crime rates, and their tendency to lower commercial rents.

The usual purpose is to provide higher capacity by increasing the number of lanes in each direction. It also allows easier creation of a green wave by adjusting traffic lights on the through route, because fewer phases are needed at each intersection.

"One-way pair" refers specifically to a single major route, divided across two streets; more extensive is when there is a grid of multiple alternating one-way streets, which is common is city centers. It is also common for frontage roads on either side of a freeway to be one-way pairs.

Flow

On a one-way pair, traffic usually flows the same way as on a normal divided highway – meaning opposing traffic follows the usual left/right convention of the country, e.g., in the United States and most of the world, northbound traffic on east side, southbound traffic on west side, following the "drive on the right" convention – though occasionally flow is switched. Following this convention allows a one-way pair to be more easily integrated into an existing network of two-way streets, as a single two-way street is effectively split into the two sides of the pair, as in the diagram below: