slip lane

A slip lane is a dedicated one-way traffic lane that curves away from a main intersection, allowing vehicles to turn (usually right, sometimes left) onto a cross street without entering the intersection proper. It sits between the turning vehicle's approach lane and the destination street, physically separated from the through-traffic conflict zone by kerbing, pavement markings, or both. The lane typically runs 30 to 100 metres depending on street geometry and design speed, with a radius suited to the expected vehicle types.

Slip lanes appear most commonly at busy urban intersections where turning movements would otherwise block through traffic or create unsafe merging conditions. They are standard at T-intersections where a road terminates into a busier cross street, allowing the minor-street traffic to peel away smoothly. Right-turn slip lanes (in right-hand traffic countries) are far more common than left-turn variants, since left turns introduce opposing traffic risk. Some intersections with high pedestrian volume restrict slip lane use during peak hours or eliminate them entirely to reduce pedestrian-vehicle conflicts at the curve.

Design and safety trade-offs

Slip lanes reduce intersection congestion and queue backup but create their own hazards. Drivers entering the slip lane may accelerate too quickly, lose sight of pedestrians crossing the destination street, or fail to merge smoothly into traffic already using that street. Sight lines are critical: designers must ensure drivers can see both the pedestrian crossing on the exit side and approaching traffic on the destination street. Poorly sightlined slip lanes produce injury crashes, particularly where pedestrian volumes are high or where drivers misjudge the speed and path of crossing pedestrians.

The term reflects the lane's function: traffic slips away from the main intersection rather than passing through it. In some regions this feature is called a turn-out lane, free turn lane, or bypass lane. Australian and New Zealand standards often refer to slip roads in similar contexts. The geometry and signalling of slip lanes are governed by local road authority standards, which typically specify minimum radii, sight distance thresholds, and when traffic control devices (yield signs, traffic signals) must be installed at the exit merge point.