What are they?
Slip roads are roads intended to help you increase your speed when joining a carriageway,
or more often a motorway. When you consider that on a motorway, vehicles will be
travelling at around the 70MPH mark and therefore you want to be reasonably close
to this speed when joining so that you don’t become a hazard to traffic already
on the carriageway. In essence, you can call a slip road an acceleration lane because
it is a stretch of road intended to be used to accelerate up to an appropriate speed.
You can find slip roads all over the UK, there are many things to consider when
joining a slip road such as will the slip road merge onto the carriageway or become
a lane itself, the speed limit on the carriageway and whether or not it is safe
for you to join. You should start by observing the speed limit on the carriageway,
this will be shown via a signpost on the slip road so that you are aware of the
speed that traffic is already travelling at. Next you need to see which form the
slip road will merge onto the carriageway, have a look at the figures below:
Figure 1: Left lane of slip road becomes a lane itself, right lane merges
Figure 2. Right lane of slip road becomes a lane itself, left lane of slip road merges
Figures 1 and 2 will be seen when using a slip road to join a motorway, when looking
at figure 1 you can see that the slip road comprises of 2 lanes with the left
of the two lanes becoming a lane itself on the motorway and therefore you won’t
have to worry about joining (but you should still check your right mirror when joining).
If you use the right of the two slip road lanes then you will have to give priority
to traffic already on the motorway. Figure 3 is a reverse of this situation, where
the left lane of the slip road has to give way to the right lane of the slip road,
you should always look at slip road signs as this will prevent any confusion when
the slip road comes to an end. Take a look at a typical slip road for a dual carriageway
shown in figure 3 below:
Figure 3 . Typical slip road * Image taken from sabre-roads.org.uk
Notice the warning signs informing you that you will be joining traffic and the
relatively short amount of space you have to join the traffic already on the cacarriageway. This type of
slip road warning sign is typical on a dual carriageway (rather than a motorway), you should make sure you don’t go over the hatched markings to join traffic. Take
a look at the following warning sign that you could see on the approach to a slip
road or on the slip road itself:
Figure 4: Warning sign informing you that you will be merging onto a main carriageway
Slip roads come in all shapes and sizes so use your initiative, don’t completely
focus on your right mirror to see if you can join because you might run out of slip
road and collide with the kerb. Its worth checking your right shoulder briefly before
joining to make sure there isn’t a vehicle in your blind spot, and if its appropriate
you should try to get as close to the speed of the traffic already on the carriageway
so you can filter in comfortably without becoming a hazard. With careful planning
you should never have to stop on a slip road unless there is heavy congestion already
on the carriageway. Also, never assume someone will give you way when you join.
How to use a slip road correctly
Fineline Driving Academy has created a short but detailed video showing the correct
way to utilise a slip road to join a carriageway, notice the speed limit sign at
the start of the slip road and the heavy acceleration used to get up to speed, also
note how early to look and see if you can join the carriageway safely.
FINELINES guide to dealing with slip roads
Use this brief guide to make sure you can safely deal with a slip road the next
time you have to use one. Practise makes perfect with slip roads so make sure you
have had plenty of experience with a variety of slip roads before sitting your practical
driving test (remember you can’t use the motorway with only a provisional driving
• Take a mental note of the speed of the traffic of the carriageway you are joining,
there should be a sign at the start of the slip road.
• Try to accelerate to as close to this speed as safely possible so you can filter
into the traffic without any trouble.
• Use every sign on a slip road, especially the one showing how the slip road will
merge into traffic already in the carriageway (See figures 1 and 2).
• Have a look as early as possible and speed up/slow down accordingly so you can
filter into traffic already on the carriageway comfortably.
• Don’t forget that the slip road will run out so keep glancing back to see when
• Check your blind spot (right shoulder) briefly before joining and be cautious
of traffic already on the carriageway that might move into your lane as soon as