Joining a motorway from a slip road (rule 259)

When you are joining a motorway from a slip road, you should give priority to traffic already on the motorway. Check the traffic, match your speed to fit safely into the flow in the left-hand lane, and do not cross solid white lines or use the hard shoulder. That is Highway Code rule 259.

Every rule on this page is quoted from the Highway Code on gov.uk (rules 253 to 273), read on 27 October 2026.

Rule 259 word for word

Rule 259 says that when you join the motorway you will normally approach it from a road on the left (a slip road) or from an adjoining motorway. You should:

• give priority to traffic already on the motorway
• check the traffic on the motorway and match your speed to fit safely into the traffic flow in the left-hand lane
• not cross solid white lines that separate lanes or use the hard shoulder
• stay on the slip road if it continues as an extra lane on the motorway
• remain in the left-hand lane long enough to adjust to the speed of traffic before considering overtaking.

How to join, step by step

1. On the slip road: check the traffic in the left-hand lane early. Rule 254 says to use your mirrors earlier and look much further ahead on motorways than on other roads.
2. Match your speed: use the slip road to match your speed to the traffic in the left-hand lane, so you can fit safely into a gap.
3. Give way: traffic already on the motorway has priority. If there is no gap, adjust your speed until there is one. Do not force your way in.
4. Stay inside the lines: do not cross solid white lines that separate lanes, and do not use the hard shoulder to join.
5. Settle in: stay in the left-hand lane long enough to adjust to the speed of traffic before you think about overtaking.

If the slip road carries on as an extra lane, stay in it rather than moving across. Green studs mark the edge of the main carriageway at slip roads (rule 132).

The theory test question

Learners search for this question word for word: "You're joining a motorway from a slip road. How should you deal with traffic already on the motorway?"

The right answer: give way to it. Traffic already on the motorway has priority, so you adjust your speed to fit safely into a gap in the left-hand lane.

Why: the first point in rule 259 is to give priority to traffic already on the motorway. Any option that expects motorway traffic to make room for you, or has you use the hard shoulder to join, goes against rule 259.

A related question asks whose priority it is on the slip road. The answer is the same: traffic already on the motorway.

Other slip road rules

• Learner drivers: rule 253 says provisional car licence holders MUST NOT drive on the motorway unless they are accompanied by a DVSA Approved Driving Instructor and are driving a car displaying red L plates (or D plates in Wales) with dual controls. Our learner drivers on motorways guide covers lessons on the motorway.
• No reversing: rule 263 says you MUST NOT reverse along any part of a motorway, including slip roads, unless directed by a police or traffic officer.
• No stopping: rule 271 says you MUST NOT stop on a slip road except in an emergency, or when told to by the police, traffic officers, an emergency sign or red flashing light signals.
• Leaving: you will normally leave by a slip road on your left. Rule 273 says to signal left in good time and reduce your speed on the slip road as necessary.

The full set of motorway rules, from lane use to breakdowns, is in our motorway rules guide.

Test yourself

Try a free mock theory test under exam conditions, or the free practice questions one topic at a time. The free diagnostic shows whether motorway rules are a weak area. theorytest.ai is independent and is not affiliated with the DVSA.

Frequently asked questions

How should you deal with traffic already on the motorway when joining from a slip road?

Give priority to it. Check the traffic and match your speed to fit safely into the flow in the left-hand lane (rule 259).

Who has right of way on a motorway slip road?

Traffic already on the motorway. Rule 259 tells drivers joining from a slip road to give priority to it.

When joining a motorway, what must you always do?

Give priority to traffic already on the motorway, and do not cross solid white lines that separate lanes or use the hard shoulder. Rule 259 puts these as "should" advice rather than a legal "MUST".

What if the slip road continues as an extra lane?

Stay on it. Rule 259 says to stay on the slip road if it continues as an extra lane on the motorway, rather than moving across.

When can you overtake after joining a motorway?

Only after you have stayed in the left-hand lane long enough to adjust to the speed of traffic (rule 259).