[user104658]

There's no reason at all for him not to be driving. Plenty of cars have engine noise loud enough to drown out outside noise, and factor in that most people have music or the radio on. Plus manufactures aim to soundproof the interiors even MORE for a smoother, quieter ride. It's not really a sense you rely on much at all for driving. You should see an emergency vehicle's lights LONG before you hear the siren, if you don't, then you haven't been properly aware of the road behind.

The question really should be, why wasn't the driver using his mirrors properly? He should have been well aware of a police car with lights flashing...