Learn to Drive

Driving lesson brief 12. Dual carriageways

Once you have improved your hazard perception and defensive driving skills you are ready to face the challenge of dealing with fast moving traffic on dual carriageways. Therefore the aim of this lesson is to learn how to deal with slip roads, overtaking and the extra hazards caused by fast moving traffic on dual carriageways. The key to dealing with this traffic is good forward observations to assess the traffic situation ahead and the effective use of mirrors to assess the traffic situation behind.

Lesson objectives
By the end of this lesson you should be able to:

  • Join a dual carriageway from a slip road by building up speed to match that of the traffic on the dual carriageway
  • Leave a dual carriageway safely by using the slip road, not the carriageway, for decelerating
  • Cross or turn right from a dual carriageway safely, paying particular attention to the extra problems this causes
  • Exercise good lane discipline and use of the two-second rule
  • Maintain good progress and overtake other vehicles as necessary
  • Anticipate the actions of other drivers and apply the hazard drill appropriately
  • Demonstrate a good awareness of what’s happening behind

Subject brief
During this lesson you will learn about dual carriageways. The term dual carriageway simply refers to a road where there is a physical separation between streams of traffic travelling in opposite directions. The barrier is usually a grass verge in the centre of the road (with or without a crash barrier).

Each side of the dual carriageway can have a number of lanes (typically two or three). Keep to the left-hand lane unless signs or road markings indicate otherwise or unless you are overtaking.

End of dual carriageway
Watch out for the ‘end of dual-carriageway’ sign. Don’t start to overtake after you see the sign, otherwise you might run out of road or even worse, find yourself facing an oncoming vehicle head on!

Clearways are not restricted to dual-carriageways. However, most dual carriageways are clearways. On roads with the clearway sign you must not stop on the main carriageway except at a layby. Clearways are designed to allow the free flow of traffic.

Junctions and slip roads
All the usual junction types can be found on dual carriageways (including traffic light controlled). On dual carriageways cars are allowed to travel at speeds up to 70 mph so you can imagine the difficulty in judging potential gaps in the traffic that you need when emerging from a junction to turn right or left onto a dual carriageway or when you cross a carriageway to turn right. To help reduce the dangers slip roads were developed. A slip road is the term commonly used to describe an acceleration or deceleration lane that helps to maintain the flow of traffic on the dual carriageway by providing a much safer way to join and leave fast flowing traffic. It is the only method allowed on motorways.

Using slip roads
A slip road can be used to build up your speed such that you can time your entry on to the carriageway to coincide with a suitable gap in the traffic from your right. The objective is to match the speed of the traffic on the carriageway such that the gap needed will be minimal.

If you are travelling at a slower speed then the gap needed will have to be much larger. Unfortunately slip roads come in varying lengths therefore it is not always possible to match the speed of the traffic you intend to merge with. Consequently, even before you commence the manoeuvre of joining a carriageway you must assess the length of the slip road to determine what speed you can attain and what gaps there are in the traffic from your right. Once you can see a reasonably sized gap coming towards you in the mirrors adjust your speed such that you can reach the speed you need to merge safely at the same time as the gap appears to your right.

You then need to check your mirrors again and possibly glance into your right hand blind spot just before joining the carriageway. Therefore to complete this manoeuvre you effectively use the hazard drill at least twice with extra observations through the mirrors.

Short slip roads
As mentioned earlier some slip roads are quite short and therefore the gap in the traffic that you need to merge in safely needs to be much bigger. In the example below it may be worth stopping at the start of the slip road ifthe carriageway was particularly busy before commencing the manoeuvre.

If possible, when a slip road is available to leave a dual carriageway you should try to avoid reducing your speed until you have entered the slip road. If the slip road is too short to allow you to do this then you would need to reduce speed before you entered the slip road. In which case you effectively use your hazard drill twice, once to reduce speed just prior to entering the slip road and once just as you begin to enter the slip road.

When you overtake on a dual carriageway you would use your hazard drill at least three times. Once to get ready to overtake, once to actually overtake and once to move back into the left hand lane.

Highway code practical references
Rules: 106-108, 116, 130-139, 173 and 288-290
Page: 113 Road works signs