I've spend some time driving in both the US and the UK and while infrastructure in the US could be improved I don't think that's the main issue.

What's different is driver training and attitude. Passing a driving test in the US is too easy to encourage new drivers to learn to drive. And an average American driver shows less respect to pedestrians, cyclists and other drivers, aggressive driving is relatively common. Bad drivers can be encountered in the UK of course but on average British drive better.

Huge SUV and pickup trucks are also part of the problem - they are more dangerous for everyone except people in such vehicle.