Dual carriageways

By the end of this topic you can

• You can join a dual carriageway from a slip road and match the speed of traffic.
• You can keep to the left lane and use the right lane only to overtake or turn right.
• You can read the speed limit and adjust to the conditions.
• You can turn right or cross using a gap in the central reservation safely.
• You can spot hazards that motorways do not have, such as side turnings and slow vehicles.

What you need to know and understand

• The national speed limit for cars on a dual carriageway is 70 mph unless signs show a lower limit.
• On a two-lane dual carriageway you should stay in the left lane and use the right lane only to overtake or turn right.
• On three or more lanes you may use the middle or right lanes to overtake, then move back when safe.
• Before crossing or turning right through the central reservation, check that the gap is deep enough to protect the full length of your vehicle.
• Hazard warning lights may be used briefly while moving on an unrestricted dual carriageway to warn drivers behind of a hazard ahead.
• The speed limit is a maximum, not a target.

Getting on: the slip road

Some dual carriageways join at ordinary junctions with a give way line instead of a slip road. In that case you must judge a gap in traffic moving at high speed, so wait for a big one.

1. Use the slip road to build up your speed to match the traffic already on the dual carriageway.
2. Check your right mirror and look over your right shoulder for a gap in the left lane.
3. Signal right if it helps others know your intention.
4. Give way to traffic already on the main road and merge smoothly into a safe gap.
5. Once on, cancel your signal and settle in the left lane before thinking about overtaking.

Turning right across the central reservation

Some dual carriageways have gaps in the central reservation that let you turn right or cross to the other side. First decide whether the gap is deep enough to protect the full length of your car.

If it is, treat each half of the road as a separate road: cross the first half when it is clear, wait in the central reservation, then join the second half when there is a safe gap. If it is too shallow and the back of your car would stick out into fast traffic, wait until you can cross both halves in one go.

Hazards to expect

• Slow vehicles such as tractors, cyclists and horse riders, which are allowed on dual carriageways.
• Side roads and lay-bys joining directly from the left, with drivers pulling out or slowing to turn in.
• Vehicles waiting in the central reservation to cross your path.
• Roundabouts at the end of fast stretches, where you need to slow down in good time.
• Lanes that end or merge, marked by signs and arrows.

Common mistakes

• Joining too slowly from the slip road. Use the full slip road to build speed while checking for a gap.
• Sitting in the right lane after overtaking. Move back to the left lane when it is safe.
• Waiting in a shallow central reservation gap with the car's tail sticking out. Check the depth before you commit.
• Treating 70 mph as a target in rain, fog or heavy traffic. Drive at a speed that suits the conditions.
• Forgetting that hazards can come from the left, such as vehicles leaving lay-bys.

Test yourself: Dual carriageways

Answer each question, then read the explanation. Questions come in a random order each time.

Go deeper

• Lane Discipline in GB
• UK Speed Limits for Cars