Challenge
Most students think 'a gap is a gap, so take it' — cautious-sounding behaviour that is nonetheless wrong. The CBR exam designer counts on that: whoever merges too early has not yet built up enough speed and still forces through traffic to react, exactly the danger the 2/3 rule is meant to prevent.
Read this section on its own page: Challenge: Merging and exiting: 2/3 of the lane and the 300-metre rule
The model
No — always use about 2/3 of the merge lane to get up to speed, even if you could merge earlier (Book p.148). Through traffic is not obliged to make room. Exiting is the mirror image: signal at about 300 metres before the exit lane, and then use the WHOLE lane, never the hard shoulder (Book p.151).
Read this section on its own page: The model: Merging and exiting: 2/3 of the lane and the 300-metre rule
Core
On the merge lane your first task is to build speed, not to merge immediately: always use about 2/3 of the lane length, even if a gap is already visible earlier (Book p.148). You must give way to through traffic; some drivers shift left to give room, but that is nowhere an obligation — so do not count on it. Is the merge lane too short to build sufficient speed? Then you stop at the START of the lane, not somewhere halfway, and only pull away once you see a gap in the traffic flow approaching in your left mirror (Book p.149). Under no circumstances end up on the hard shoulder — further along it a broken-down vehicle could be standing there (Book p.150). Exiting works as a mirror image, with its own numbers: signal at about 300 metres before the start of the exit lane, using the green hectometre markers as an aid (Book p.151). Then use the WHOLE exit lane — here too: never the hard shoulder. One exception to the ordinary overtake-on-the-right rule applies specifically to the exit lane: to the right of the block marking you may overtake slow-moving drivers on the through lane on the right, provided that is needed for smooth traffic flow and you hinder or endanger no one (Book p.153).
Read this section on its own page: Core: Merging and exiting: 2/3 of the lane and the 300-metre rule
Why it matters
Merging too early near Clinge on the A37 means joining at a speed still too low for the through lane — through traffic then has to brake or swerve unexpectedly. And whoever only signals halfway along the exit lane near Graauw gives following traffic too little time to anticipate; the 300-metre rule exists precisely to guarantee that reaction time.
Read this section on its own page: Why it matters: Merging and exiting: 2/3 of the lane and the 300-metre rule
Frequently asked questions
‘You must merge as early as possible, as soon as there is a gap in the traffic, even if you are still only at the start of the merge lane’ – is that true?
No. Always use about 2/3 of the merge lane to get up to speed, even if you could merge earlier
‘Drivers on the through lane are legally required to move left and make room as soon as you want to merge’ – is that true?
No. You must give way to through traffic; some drivers move left to give room, but that is not obligatory, so do not count on it
‘If a merge lane is too short to get up to speed, you may stop somewhere halfway along the lane and wait for a gap’ – is that true?
No. At a too-short merge lane you stop at the START of the lane, not halfway, and only pull away once you see a gap approaching in your left mirror
‘For exiting you simply signal 'in good time'; the book does not name an exact distance for the start of the exit lane’ – is that true?
No. Signal at approximately 300 metres before the start of the exit lane, using the green hectometre markers as an aid
‘Overtaking on the right is never allowed on an exit lane, not even of slow-moving drivers on the through lane’ – is that true?
No. On the exit lane you may, to the right of the block marking, overtake slow-moving drivers on the through lane on the right, provided it is needed for traffic flow and no one is hindered