Slip lane

Slip Road onto United States Highway 2 in Minnesota (right-hand-traffic). The length of this slip road has been designed to allow cars to reach 65 mph (105 km/h) at the end of the road in order to join the highway safely.

Slip roads are the only way to join and leave motorways. However slip roads may also be seen on some dual carriageways and even single carriageways with heavy traffic throughput, or at junctions where there may be a high risk for a collision. They are generally long enough to allow a car to accelerate and join the main carriageway at the speed of traffic, reducing congestion. Furthermore it is also safer as the speed difference between vehicles isn’t that much, which helps prevent rear-end collisions.[2] However, in some cases especially on urban motorways, the slip road may continue on the motorway as another traffic lane.

Illustration (left-hand traffic): the blue vehicle in the slip lane must give way to the green and red vehicles even though the latter is at a give way control.

Some intersections especially controlled by lights offer a slip lane that allows cars to bypass the lights when turning. This helps ease congestion and improves journey times as people turning don’t have to stop at the light and can continue at the same speed.[3] There are two types of slip lanes at intersections: slips lanes that end and require traffic to merge in order to join the main road and slip roads that continue onto the main road as another traffic lane. However, despite slip lanes being very dangerous to pedestrians, it might actually be safer in some cases to build a slip lane to prevent vehicle-vehicle crashes.[4]

Some short slip lanes at junctions may continue onto the main road for a short distance to allow drivers to accelerate and safely join the main road. Likewise, some slip lanes may start extra early to allow drivers to decelerate. These lanes, named Deceleration lanes, are mostly seen on motorways were the slip road is extremely short or on fast roads[5]

Before entering a slip road, drivers must look to ensure that their blind spots are clear of other motorists, cyclists, and pedestrians. Than drivers must give way to any pedestrians crossing the slip road road. Before joining the main road from a slip road, drivers must give way to all other traffic even when that traffic is faced with a give-way or other traffic controls.[6]

When poorly designed, slip lanes can be a dangerous design element. For reasons of urban design and pedestrian amenity, many road controlling authorities actively remove them in urban and suburban settings.[7][8] Slip lanes may need to be removed if considerations such as pedestrian safety grow to a point where they over-ride the desire to facilitate free passage for cars.[9][10]

To minimise risks of collision, slip lanes can be shaped to enter the traffic flow at a higher angle than the 45 degrees shown in the first sketch. Such lanes are called high entry angle slip lanes.[11]

• Interchange
• Advanced stop line
• Continuous-flow intersection
• Hook turn
• Quadrant roadway intersection
• Seagull intersection
• Superstreet
• Texas T
• Texas U-turn
• Turnaround