Joining & Leaving a Dual Carriageway —
Speed, Mirror, Signal

Joining a Dual Carriageway

The slip road exists to let you build up to the speed of the traffic you're joining before you merge — not to wait at the end of it for a gap. Use the full length available to accelerate, watching the traffic already on the carriageway as you go.

Speed, Mirror, Position, Signal, Blind Spot

As you build speed on the slip road: check your mirrors to see what's approaching and how fast, choose your target gap, signal your intention, then take a final blind-spot check immediately before you move across — your mirrors can't show you everything, and this is the one check that fills the gap.

Joining at a Direct Junction

Not every dual carriageway has a slip road. Where you're joining directly from a side road with no run-up, you need a gap large enough to pull away and get up to speed without forcing the traffic behind you to brake hard.

Lane Discipline Once You're On It

In practice: don't sit in the right-hand lane once you've finished overtaking, and don't use it as a default cruising lane. It's there for overtaking and turning right, not for general use.

Leaving a Dual Carriageway

Position yourself in the left-hand lane well before your exit, and signal in good time. Keep your speed up on the main carriageway itself — braking there, rather than on the deceleration lane or slip road, catches out traffic behind you. Slow down once you're committed to the exit, not before.

Instructor's tip: "Two things catch learners out here: hesitating on the slip road and losing your gap, or braking too early on the carriageway when leaving. Both come from not trusting the full length of road you've been given — use all of it."

Right Turns Across a Central Reservation

Turning right across a dual carriageway's central reservation is one of the higher-risk manoeuvres you'll meet — you're crossing one carriageway of traffic to wait in the gap, then crossing a second. If you're not certain there's a safe gap on both sides, wait for a clearer one rather than committing.

Source: Highway Code, Rule 137 (dual carriageway lane discipline).