that's also a problem that stems from driving too fast. but at least europeans tend to drive slower when the road conditions require it. also, these obstacles are only placed in areas, that are already low-speed (30km/h = 18mph limit). sure, you can drive arount those obstacles like a slalom-racer, but then you're violating the speed limit - and common sense - again. those limitation won't hold an idiot, but they'll give the rest of the population an incentive to think about what they are doing - and thus reducing the probability of accidents. and you'll probably avoid a surveilance state, where every "concerned" citizen uploads speed-trapping software to his webcam/smartphone, and hunts for sinners.