Aclimbing lane,crawler lane of the Road (UK[1]), ortruck lane, is an additional roadwaylane that allows heavy or underpowered vehicles to ascend a steepgrade without slowing other traffic. They are typically used by large trucks orsemi-trailer trucks, which go uphill more slowly than they travel on level ground. They are often used on major routes such asmotorways andinterstate highways.
Some climbing lanes extend slightly over the crest of the hill, to allow slow vehicles to regain speed.
Astrucks andrecreational vehicles must uselow gear to descend slowly, an additional lane may also be built on the downhill side. This prevents the vehicles from overusing theirbrakes, which may overheat and cause arunaway vehicle.
Some downhill truck lanes may also have a nearbyrunaway truck ramp, which can help catch and slow down runaway trucks that have brake failures to prevent a serious collision.