[Katana]

I think it's a good idea to a certain extent, but if you remove too much i think it would be risky. It might work in a smallish town, but in a city you need markings and lights to maintain a certain order with the deluge of cars.
In england we have roundabouts (what americans call turning circles) and they work very well for the most part, you just have to see who is coming from the right and properly indicate. Bigger roundabouts have traffic lights because it would be difficult to get on them at peak traffic times, as people coming from busy routes use the cars in front as a spearhead and no gaps are left for people to merge onto the roundabout if they need to go elsewhere.

It's just awareness really, if there is a sign up ahead that says you have right of way you barge along and expect the other people to give way, if the sign isn't there, you'd probably slow down and take more notice of the other cars and proceed more cautiously.
It can have a the opposite effect in some people where they panic at an unfamiliar junction with no markings/signs/lights and make mistakes.