SafeSpeed wrote:
...So the right answer changes with the size of the gap. In fact if you define it as a 'gap' then it's probably better not to use it...
Actually, that brings up a point of logic that I'd never considered in my first answer, and I think it may explain why this situation rings alarm bells:
If the gap is closing, then it is unwise to accelerate into it, for all the reasons given previously.
But if the gap is constant, or is even growing, this vastly increases the chances that the driver will suddenly become aware that he isn't making any progress on the vehicle in front and is out in L2 for no reason whatsoever, at which point he may well feel a bit sheepish and leap back into L1 pronto, without checking for the undertaking vehicle that he won't expect to be there. Furthermore, the fact that he's been out there drifting along without gaining on the vehicle in front makes it seem highly likely that he's been "daydreaming" and won't have spotted your approach at all.
So in either circumstance (ie that there is a "gap" between the two vehicles rather than coming across them a fair distance apart) I'd regard the undertake as posing an unacceptable risk, versus the alternate strategies available at that time.
As an aside, what a great first post Mr Flintoff!.
This is one of many, many scenarios that have been brought up on here where previously I might have subconsciously dealt with it without really justifying my actions to myself. But talking through it like this equips me with a mental checklist, a positive strategy, and a clear justification for my actions the next time it arises. I presume I'm not alone in noticing this, and wonder how many other posters have felt this benefit too.