Problem:

Flies have a short lifespan, therefore evolution should technically happen over a shorter period of time (years).
Flies die all the time from getting hit by cars on the motorway.
Those flies that don't go near the motorways have a greater chance of reproducing.
If this was an advantage (motorway avoidance = not dying), shouldn't more and more flies be avoiding the motorway?
Cars have been around since, roughly ~1950. That's 60 years.

Question: Why don't flies avoid the motorway?

Please explain.