Contraflow

Contraflow is the situation in which the direction of traffic flow on one or more lanes of a road or carriageway otherwise considered to be one-way is switched to be the opposite to that observed on that road's parallel and directly adjoining lane or lanes.

Motorway or dual-carriageway contraflows

Contraflows are often used on multi-lane roads during roadworks periods in order to maintain maximum traffic flow whilst giving safe space for the works to be undertaken. This can be done in a variety of ways, with either the entire carriageways traffic transferred to leave a completely clear space for the works to be undertaken within. However, on busier routes, or narrow dual carriageways it is not always possible to do this whilst maintaining sufficient traffic flow. In such circumstances, one or two lanes of traffic may be moved onto the contraflow, with the rest remaining on their normal side, thus giving extra space for the works. Almost without exception, on motorways a contraflow will involve the hard shoulder being used as a running lane, and more often than not the carriageways will be re-lined with narrower lanes.

Safety in contraflows is important, especially on motorways and fast dual carriageways where traffic may otherwise expect to flow freely at 70 mph. Cones have therefore given way more recently to concrete or steel dividers between opposing flows, and in many locations with long term roadworks a 40 or 50 mph speed limit is enforced via average-speed cameras.

Urban contraflows

The other common type of contraflow is in an urban environment, where a one-way street may have an opposing direction cycle lane installed, or less commonly a contraflow bus lane. In the latter instance, the road may have previously been two-way, but reduced to speed up a bus route.