> because modern cars are so heavily sound-proofed they don't hear a bicycle bell anymore

Agreed. I had a supercharged V8 Jaguar that I could barely hear.

And my Audi has a system that actually pumps engine noise into the cabin, so you can hear that, but not the outside world.

The Fire Department I was at was looking at "thumpers" - augmentations to sirens that make cars in front of them vibrate (a la those people playing too much bass too loud).

Not just sound proofing, but inattentiveness. I've been behind people on semi-rural quiet roads with my 40,000lb fire engine behind them, lights, sirens, and airhorns, and they've driven for a mile or two completely oblivious.