sammy.se":3f71j9i5 said:
If the side road has a give way, the side road needs to wait. The driver of the main road needs to drive safely to the road conditions, so if for example, the main road was 40mph, and s/he slows to 20mph, that is not appropriate, but... the driver behind will still be at fault for rear ending - that is a separate subject.
Basically, courtesy is fine, but you still have to drive appropriately. The driver behind was either too impatient/lacks courtesy, or, the driver slowing down did so in an inappropriate manner.
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Having only passed my driving test a couple if years ago I'm pretty sure the answer is this - failing to check that the car behind has sufficient space to ensure braking is safe, when said braking is not required for safety or an emergency. I think the highway code states you should ALWAYS check you rearview mirror before braking.
Chances are the car behind was too close; and had been for sometime - or the driver who slowed / braked hadn't checked the rear mirrow either before the manouvre,
nor in the preceeding few minutes to notice the rear car was too close.
@ transatlantic - I was under the impression that if the outer lane is empty with nothing approaching, and there is someone on the slip road (which I check as a matter of course), changing lanes was the common practice - safer for you and them - expecting them to speed up or slow to allow you to pass when the outside lane is free (or has sufficient space when traffic is heavier) is a little...... dare I say "this is MY space you work around ME".
You control your car, get out the way and let them do whatever without possible incident.
I've done a fair bit of motorway driving going to and from London for work and if I'm honest, I've seen far too much of the "I'm not getting out of the way" mentality when there was easily space to do so.