Motorway Slip Roads

Motorway Slip Road Rules

When it comes to slip road rules, it is important to know what to do, what you are NOT allowed to do and how to execute the manoeuvre.

You will enter a motorway via a slip road. When joining a motorway, you should:

  • Use the slip road to adjust your speed to match the speed already on the motorway. This is very important, otherwise, you could cause an accident.
  • Give way to traffic already on the motorway
  • Make sure the there is a suitable gap in the left hand lane on the motorway before emerging
  • Use the MSM (mirrors, signal, position) routine PSL (position, speed, look) before emerging into a safe gap on the left.
  • If you are already on the motorway & see another vehicle on the slip road, you should make an attempt to move to the middle lane, to allow the vehicle to enter the left lane.


Motorway Slip Road Markings

Motorway slip road markings come in the form of white lines with separation gaps dividing the slip road from the main carriageway. There are also green reflective studs, otherwise known as cats eyes on the right-hand edge. These reflective studs are there to inform drivers what road position they are in when driving in the dark. They can be found on single carriageways, dual carriageways and on motorway slip roads.

Motorway Slip Road Signs

Motorway slip roads come with road signs informing you of the lanes and the slip road. Sometimes, you may encounter what I call a ‘continuation’ lane, and this is represented by a continuing arrow in the left lane. Motorway slip road signs are blue in colour and are square/rectangle in shape. Dual carriageway road signs are green in colour and square/rectangle in shape.

Slip Road Highway Code

The Highway Code states that traffic on the slip road must give way to traffic already on the carriageway/motorway. Traffic should only merge if they can move to the left lane without affecting anyone on the main carriageway/ motorway.

What to do if you run out of slip road

If you run out of slip road, ultimately, you are NOT allowed to merge onto the main carriageway if it is not safe to do so. If you are NOT able to safely merge, you must come to a stop. If you stop on a motorway/carriageway slip road, you will need to plan a larger gap before attempting to merge onto the main carriageway.

How to join a dual carriageway from a slip road

It is important to know how to join a dual carriageway/motorway from a slip road safely. Here is a step-by-step guide:

  1. When first entering the slip road, you should build your speed up to match the main carriageway
  2. You should apply the MSM routine to inform other road users of your intentions
  3. You should apply the PSL routine to check your road position, speed and observations on the approach
  4. You should assess the traffic flow in the left-hand lane of the carriageway/motorway
  5. Is there a safe gap for you to emerge into? If yes, then proceed to move over
  6. If there is not a safe gap, you should either increase your speed to get ahead of a vehicle in the left-hand lane or decrease your speed to pull in behind the vehicle in the left-hand lane. Either way, you need to be mindful of the space/gap left on the slip road.
  7. If you run out of slip road, you should aim to STOP and give way until there is a safe gap for you to merge onto the main carriageway.

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