What is a slip road?

A slip road is a section of short road which vehicles join or leave a larger road such as motorway or dual carriageway.
Whether you’re preparing for your driving test, brushing up on the highway code or simply curious about their purpose of a slip road, you’re in the right place. In this article, we’re going to break down what a slip road is, the different types of slip roads, how to use a slip road and useful tips to master your next encounter with a slip road.

A slip road – also known as a slow lane or filter lane – is a short section of road designed to let vehicles join or leave major roads such as motorways or dual carriageways without stopping at a junction. Slip roads are one-way, matching the same direction as the road you intend to join. You’ll typically find one on each side of a motorway.
A slip road provides a transition area for drivers to either safely join the main carriageway by gradually increasing speed to match the flow of traffic already on the motorway or exit safely by slowing down before reaching regular roads.

There are two main types of slip roads. Road signs will indicate what type of road you are on.
The first one requires you to merge into traffic at the end of the slip road, with the slip road narrowing before it disappears altogether. The sign will show an arrow pointing diagonally into a larger road if you are required to merge with traffic. This is the most common type of slip road. The second is where the slip road becomes a new additional lane. Here, you’re already positioned as part of the main road and can move over when you are ready. You should stay in the left-hand lane long enough to adjust to the speed of traffic before overtaking. A sign with a line coming in at an angle before running parallel with a larger road indicates that the slip road will form a new lane rather than disappearing.

When joining a motorway or dual carriageway via a slip road, use the slip road to accelerate so your speed matches the traffic on the road you are joining and always staying within the speed limit. Joining at a slower speed than the vehicles already on the road can create a hazard as they may be forced to break suddenly, posing a threat to other road users.
As you accelerate along the slip road, look for a gap in the traffic and aim for it – don’t forget to indicate. Make sure to use your right-wing mirrors and check your blind spots, so you’re fully aware of what’s happening on the road you’re merging into. This becomes even more crucial if you’re on a slip road that merges, as you’ll need to be certain there’s enough space for you to move across safely. For new drivers, this process can feel a bit daunting at first, but it becomes easier with experience. In most cases, drivers already on the main road will be aware that a slip road is feeding traffic onto their lane. Often, they’ll move over one lane to the right or slow down slightly to make room for vehicles joining from the slip road.

Slip roads also allow you to leave a dual carriageway or motorway. When exiting a motorway or dual carriageway, most slip lanes act as deceleration lanes, giving you space to reduce speed. Road signs will indicate when you're approaching an exit. Move into the left-hand lane so that you can drive onto the slip road to exit. Ensure that you do this in sufficient time, so you don’t cut across traffic or miss your exit.
It may be tempting to slow down in advance before exiting, however, doing so will hold up traffic on the main road. This can increase congestion and may also pose risk to yourself and nearby drivers. It’s important to use the slip road to slow down. As you approach a slip road, you’ll see countdown markers with angled white lines, indicating the distance to the start of the slip road: 300 yards, 200 yards, and 100 yards. When exiting, ensure that you indicate at the 300-yard marker to signal to other drivers that you’re coming off the motorway or dual carriageway.

• Use indicator signals well in advance to inform other drivers your intention to change lanes or merge
• Continuously check mirrors and blind spots • Avoid jerky movements or hesitation as this may distract nearby drivers • Don’t force yourself into a gap if you’re unsure whether the gap is suitable to merge into, slow down and wait for a safer opportunity • When leaving a motorway, your judgement of speed may be affected. Ensure you check your speedometer and adjust your speed to that of the road ahead • Some slip roads are short with sharp bends – look for signage indicating the severity of the turn • Practice using slip roads at quieter times of the day, the more practice you get with slip roads the more confident you’ll become

Reflective studs that indicate a slip road are green in colour.

Whilst most drivers will be accommodating and move lanes to give you space to join, there may be situations where they are unable to do so. If you’re in a situation where it is not safe to join, you should stop on the slip road and wait until a suitable gap becomes available.

You should only stop at the end of a slip road if you are unable to join the motorway or in an emergency situation, for example if your vehicle experiences a mechanical failure, where you should pull over as far left as possible.

Yes, if there are two lanes you can overtake. However, remain cautious as slip roads are primarily used for drivers to adjust their speed prior to joining or exiting a major road. If the vehicle ahead is very slow, assess carefully and overtake only if it’s safe.

Yes, you must give way to traffic on the major road. According to the Highway Code, the traffic already on the major road have priority on a slip road.

Unless otherwise stated, the speed limit on a motorway slip road is usually 70mph. For other road types there is no standard limit, so you should refer to signs along the slip road to indicate the maximum speed limits.

Whilst slip roads are predominately found at dual carriageways and motorways, they can also be found on slower more urban routes.

Jamiton is where traffic slows down to around 12mph without any obvious reason. It’s usually caused by one driver breaking too harsh, causing a ripple effect that slows everyone behind. These usually happen near slip roads where merging disrupts the flow of traffic. To prevent jamitons, avoid sudden breaking or hesitation.
Now that you know more about slip roads, why not take a look at some of our other helpful articles about car ownership.