> municipal governments adversely affect traffic flow by lowering speed limits because those lower speed limits generate more ticket revenue.

I don't know about the US because the US is weird, but:

* at 30kmph the rate of fatalities in case of a car hitting a pedestrian is basically 0%, at 50kmph I think it's 5% or more

* at 30kmph collisions are much easier to avoid due to the increased reaction time and the decreased braking distance (I don't remember the exact numbers)

* at 30kmph you can hold a conversation at normal speech levels next to a moderately busy road, at 50kmph you will have to shout (and not even notice it due to the high ambient noise)

Etc.