I can guess a few reasons:

* Cars tend to be bigger i.e. more dangerous in the US

* Drink driving seems to be more acceptable in the USA.

* The driving test in the UK is much tougher than even the toughest us state

* Most of the US don't have mandatory annual vehicle inspections to check they're safe and roadworthy

Big and straight allows higher speeds and less need to pay attention. Lane width is a major contributor to the actual speed driven.

It's counterintuitive, but broad and straight roads are often more dangerous, as they invite faster driving.

Faster *inattentive* driving.

I'm always kind of surprised how terrified Americans visiting the UK are, when they see the kind of speeds people drive at here.

If you're coming here on holiday from the US and you're planning your route using Google Maps, double the time estimate. You won't like the speeds it expects you to drive at.

> roads are big and straight

To accommodate big cars.