Junctions

Using a filter lane at a roundabout to join a dual carriageway

This manoeuvre changes character partway through - it starts as lane discipline on a roundabout and ends as speed-matching onto a faster road, and both halves need their own attention.

Advanced Step-by-step lesson Common mistakes

This video has no narration. Follow the written steps below.

Practical test

Why it matters

This tests whether you can adapt from one skill (lane discipline) to another (speed matching) within a single, continuous manoeuvre.

What to look out for

Two manoeuvres in one

This starts as lane discipline at the roundabout and finishes as speed-matching onto a faster road - treat them as separate phases.

Don't drift back toward the roundabout

Once the lane is chosen, follow its markings cleanly and keep your attention moving forward and to the mirrors, not back toward the roundabout.

Key steps

1 Read the signs and road markings early so you know the filter lane leads towards the dual carriageway, before you're committed to a lane.
2 Check mirrors, choose the lane in good time, and avoid drifting toward the main roundabout lanes.
3 Hold a smooth line through the filter lane, keeping space from traffic ahead.
4 As the lane becomes a slip road, look well ahead and start matching your speed to the dual carriageway progressively.
5 Check mirrors and the blind spot, then join once there's a safe gap in the traffic already on the carriageway.

Common mistakes

Treating the filter lane as automatic priority

Stay alert for lane markings, traffic ahead, pedestrians, and cyclists before you continue through it.

Still thinking about the roundabout

Once you're committed to the filter lane, shift your attention to the slip road and the faster road ahead of it.

Building speed too late

Use the slip road progressively, the same way you would joining any dual carriageway, so you're not accelerating hard at the very end.

Example scenarios

Illustrative, AI-generated examples - not real photographs.

Stopping in the filter lane instead of matching speed with traffic already on the carriageway — it's a merge, not a queue.

Leaving the merge too late — a filter lane is marked by a solid white line, and once it runs out there is no room left to blend in safely.

Highway Code

This lesson is a revision aid, not a replacement for The Highway Code.

Rule 184

On approach, use Mirror-Signal-Manoeuvre at all stages, decide as early as possible which exit you need, give an appropriate signal (see Rule 186), and time your signals so as not to confuse other road users.

Read Rule 184 on GOV.UK

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