A Dual carriageway is 1 lane of traffic (usually 2 or more travelling in the same direction) which is divided by a central reservation and barrier that separates the other carriageway travelling in the opposite direction. Regardless of the number of lanes, a road is a single carriageway unless separated by a physical barrier.


Roads in the UK are categorised into:
B roads - country or residential areas
A roads
- high speed single or dual carriageways
M roads
- motorways always dual carriageways


Dual carriageways can be challenging for drivers. This is often due to the high speeds involved along with the all-important observations.


Joining dual carriageways


You will join a dual carriageway from a slip road leading off either a road or roundabout. The speed at which you join the slip road varies depending on the circumstances. It is important to gain sufficient speed to equal those already on the carriageway. Joining the carriageway at 40 mph whilst traffic already on the carriageway is at a speed of 70 mph can be highly dangerous.


Traffic isn't always travelling at 70 mph however. Observe traffic on the carriageway at the earliest opportunity. This can be from the road or roundabout or even from a bridge that crosses over the carriageway before you join. This will provide you with a good sense at which the speed you will need to reach before joining. Traffic especially during rush hour can be slow or even stationary as you join a dual carriageway. Be prepared to stop just before the junction line if necessary.


The key to joining a dual carriageway is to accelerate down the slip road to match the speed of those already on the carriageway. Whilst accelerating, make quick checks to the right and alternate with the direction you are travelling. Briskly keep checking between the two looking back and forth as though watching a tennis match. Although the main focus should be in the direction you are travelling, brisk and frequent looks to the right is important.


Take care where there is a dedicated lane for vehicles joining a dual carriageway. Vehicles in such a lane do not have to give way. However, if you are in a dedicated land watch out for fast moving vehicles that have not noticed, or are ignoring, the dedicated lane.


Driving at speed


The faster you travel in a car, the less turning of the steering wheel is needed. When altering direction on a dual carriageway at 70 mph, steer the wheel slightly and gently.




Short slip roads


Although the slip road used to allow traffic to join a dual carriageway is often long enough to allow a vehicle to accelerate to a speed to match those already on the carriageway, occasionally there are short slip roads.


If the dual carriageway is busy, it may be necessary to wait at the start of the slip road for a suitable gap to accelerate into.


Driving on dual carriageways


Once on the carriageway, stay in the left lane until you have had a chance to adjust to the situation and remember to keep a safe distance from vehicles in front. The 2 second rule will help with this. The speed limit of dual carriageways is 70 mph. You are expected to drive at the 70 mph national speed limit if it is safe to do so. If you are behind a slow moving vehicle, overtake if possible.


Look well ahead as well as your immediate surroundings on dual carriageways. Traffic that has stopped or reduced speed ahead can be dangerous for fast approaching traffic.


Dual carriageway overtaking


The MSPSL routine needs to be applied:
Mirrors - check the interior and right mirror. Look for vehicles that may be approaching at speed from behind to overtake you. If you are confident it is safe to overtake.                   Signal - apply a signal to the right.
Position - keep a good distance behind the vehicle you intend on overtaking by using the
2 second rule. If driving too close to the vehicle in front, the driver may not clearly see your intention to overtake.
Speed - gently steer to the right and once in the right hand lane accelerate past the vehicle.
Look - once in the right lane, check the interior mirror for approaching traffic behind. Wait for the front of the vehicle you have just overtaken to appear in your interior mirror, then check your left mirror, signal to the left and gently move back into the left lane.


Dual carriageway reflective studs


Dual carriageway reflective studs or cat's eyes are designed to be most effective in poor light conditions by reflecting light. The colour of the studs always has the same placement on motorways and dual carriageways.


Red - Dual carriageway reflective studs are placed along the hard shoulder of both motorways and dual carriageways. They can also be seen on the left of certain A or busy B roads.


Amber - Dual carriageway studs are placed to the far right, running alongside the central reservation.


Green - Dual carriageway studs indicate where a junction either joins or leaves a Dual carriageway, called a slip road or deceleration lane.


White - Dual carriageway studs are placed between the lanes of dual carriageways or motorways.


Blue - Dual carriageway studs can occasionally be seen and are for the use of the emergency services.


Dual carriageway junctions


As you are driving on the dual carriageway, other vehicles may also join. Keep an eye for slip road junction ahead and other vehicles joining. On "A" type dual carriageways there may even be standard "T" type junctions. Whilst you do have right-of-way over vehicles joining, you should make their joining as safe and easy as possible. Maintain a steady speed. However, if you feel you may impede another vehicle joining, either if safe to do so by initially checking your mirrors, gently decrease speed or change into the right-hand lane by use of the MSPSL routine.


Turning right on dual carriageways


Occasionally, there may be a need to turn right on a dual carriageway. If so, ensure you are in the right-hand lane in good time. Use the MSPSL routine for turning right. This will need to be completed in good time as you are driving at speed and will need to provide traffic behind with plenty of warning. There will be a slip road speed reduction lane to enter before the turn. Ensure you do not slow down too abruptly before you enter this lane as it can be dangerous for vehicles behind. If a vehicle is following too closely before you turn right, you may need to gently slow down a little sooner to allow them enough reaction time for you to make the turn.


Dual carriageway roundabouts


You are travelling at high speed, slow down gently in good time and ensure you do not leave it too late to start slowing. Dual carriageway roundabouts are often large multi-lane. The MSPSL routine needs to be applied for which ever direction you are taking. If turning left or following the road ahead at the roundabout, remain in the left lane. If turning right at the roundabout, you will need to move into the right lane in plenty of time before the roundabout. If you are unable to take the right lane due to traffic density, remain in the left lane and either turn left or follow the road ahead. Do not turn right / 3rd exit from the left lane. A vehicle may be following the road ahead (2nd exit) from the right-hand lane which can cause a collision if you turn right (3rd exit) from the left-hand lane. see the roundabout sheet for more information on large and double roundabouts.








Exiting a dual carriageway


Approaching exits on Dual carriageways you will see countdown markers. The 1st one you see will have the 3 slashes signifying 300 yards from the exit.


When you see this marker, check your mirrors. When you get to the "3" marker signal left.


Pass the 300-yard marker is the 200 yard and finally the 100-yard marker before exiting dual carriageway into the deceleration lane. Unless road / traffic conditions demand, do not slow down until you reach the deceleration lane. You will need to gently slow down on the exit junction deceleration lane to the appropriate speed for the road or roundabout you will be joining. Cancel your signal and then perform the MSPSL routine and the next junction as normal.


Dual carriageway rules


The following are dual carriageway rules and regulations that must be followed.


Dual carriageway speed limit


The national speed limit on dual carriageways unless stated otherwise by road signs or light signals is 70 mph.


Dual carriageway undertaking


Undertaking on a dual carriageway is only permitted when a vehicle is using the right lane for turning right or in situations of high traffic density, if your lane is travelling at a great speed than the fast lane.


Dual carriageways and cyclists                                


It is not illegal for a cyclist to ride on a dual carriageway unless stated otherwise by signs. It is however extremely dangerous and not advised.


Dual carriageway parking


With the exception of parking lay-bys and service stations, drivers are not permitted to park on the hard shoulder of a dual carriageway.


Dual carriageways and motorways use chevron road markings on the entrance and exit slip-roads. Chevron road markings surrounded by a white broken line can be entered if safe to do so. Chevron road markings with a solid continuous white line boundary must not be entered except in an emergency.