I don't know about enforcement frequency, but what I have seen here is that there is a lot of traffic calming, and deliberately engineered chokepoints where tra

I don't know about enforcement frequency, but what I have seen here is that there is a lot of traffic calming, and deliberately engineered chokepoints where traffic must slow down considerably or stop for cars heading in the opposite direction. This isn't just central London, either, but in the suburbs. The complex junctions with multiple islands for pedestrian crossings (often carefully fenced such that you _have to_ cross at the zebra stripes proper) are another difference from the US, and structurally contribute to this effect.