What is a dual carriageway? Speed limits and safety tips

Lesson Type
Last updated: 2 Nov 2020

At some point during your driving lessons, you’ll have to tackle driving on dual carriageways. This can seem like a daunting idea at first, but once you’ve mastered the basics of being on the road, getting to grips with driving at high speeds isn’t as challenging as you might think.

What is a dual carriageway?

Dual carriageways are high speed main roads that have any kind of physical separation between the two streams of traffic, often a grass verge. They usually have two lanes of traffic going in either direction, but it is possible to find dual carriageways with more or less than two lanes. As a learner driver, you are permitted to drive on a dual carriageway with your driving instructor or supervising driver, as long as you are displaying L-plates.

Joining a dual carriageway

One of the main concerns learner drivers have about dual carriageways is how to join them. In most cases, you will use a slip road to join a dual carriageway, filtering into the left hand running lane of the dual carriageway once you have built up speed. Building up your speed on the dull carriageway is essential, as you need to be able to keep up with the speed of other motorists who are already travelling on the carriageway.


The national speed limit for dual carriageways is 70mph, unless otherwise stated, but this doesn’t mean that everyone on the road will be travelling at 70mph. Steadily build up your speed on the slip road and start making observations at the earliest possible opportunity. This will be about half way down the slip road, and, at this point, you should apply the routine.

Check your interior and right side mirror and signal to the right. At this point, you should be able to see traffic in the live lanes of the dual carriageway in your right side mirror. Check for a gap in the traffic which will allow you to join the carriageway, adjusting your speed if necessary. Assessing when a space is big enough for you to join the dual carriageway is a skill which might take a bit of getting used to, and you may need to speed up or slow down to fit into the flow of traffic. Make sure you continue checking in your mirrors and once over your right shoulder at your blind spot, before joining the live lane.

What speed should I drive on a dual carriageway?

As a learner driver, you won’t be used to driving at high speeds, but driving at speed on a dual carriageway is actually safer than driving slowly. Once you’ve joined the carriageway, adjust your speed to keep up with the flow of traffic. Stay in the left lane after you’ve merged on to the carriageway, and ensure you have left a safe distance between you and the vehicle in front.

On your driving test, the driving examiner will be looking for you to show that you can keep up with the flow of traffic and that you are comfortable and capable of driving at 70 mph. Of course, driving at 70 mph is not always possible, so only drive at the speed at which it’s safe to do so at the time.

Overtaking on the dual carriageway

You should stay in the left lane as long as the flow of traffic ahead is in keeping with your speed. If there is a slow moving vehicle ahead, check your interior and right side mirror to see whether it’s safe to overtake. If the right hand lane is clear, check over your right shoulder in your blind spot, signal if the lane is clear, and overtake.

Once you’ve passed the slow moving vehicle, check in the left side mirror to see when it is safe to pull back over into the left hand lane. Pulling back in too close to the overtaken vehicle is dangerous, so you should wait until you can see the full front of the vehicle in your left side mirror before indicating and moving back across into the left lane.

Exiting the dual carriageway

As you approach the exit you plan to take, stay in the left hand lane, even if there is a slow moving vehicle in front of you. The exit slip road will be on the left hand side of the dual carriageway, so overtaking at the last minute can be very dangerous. If you’re not sure how close you are to your exit, look out for the exit junction sign and the green countdown marker signs at the side of the carriageway. You should apply your left indicator when you reach the countdown markers.

Although you will be used to applying your brakes when you turn off a single carriageway road, you shouldn’t use your brakes until you’re on the exit slip road. Braking on a dual carriageway (unless absolutely necessary) can be dangerous, as drivers behind do not expect you to slow down abruptly. Instead, ease your foot gently off the gas pedal as you approach and join the exit slip road.

Turning right on dual carriageways

On some dual carriageways it’s possible to take a right turn. To do this, you need to position yourself, using the MSPSL procedure in the right hand lane. Ensure you do this in good time before you approach the turning, and that you’re signalling right as you approach the turning.

There will be a small slip road before the turning in order to allow you to gently reduce your speed. Make sure you don’t slow down too abruptly upon your approach, as this can pose a danger to the drivers behind. Instead, ease off the gas pedal, ensuring that there is a safe distance between you and the vehicle behind.

When waiting to cross the other carriageway, remember that cars will be travelling faster than you’re used to and that you will need to leave a bigger gap to cross.