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Can you also hear cyclist approaching from behind? if so, can you also tell whether they'll overtake or undertake you? were you able to tell how many cars is behind you while in noisy traffic? can you tell whether a car is about to turn left? etc.

It is highly advisable to not rely on your hearing as they don't give you as much information as looking back do.

I think I've (you've) found the nub of the issue here - we're not comparing eggs with eggs.

Dense city centre traffic =/= Faster roads with lighter traffic.

I appreciate hearing is of less importance in the latter but would still submit that voluntarily blocking out a sense in a life and death activity is not a sensible course of action.