I have a few comments I'd like to share on this issue.
During my last couple of holidays in America (New York City and area, San Francisco and area) I found the road junctions very frustrating. I can't believe how slow the progress is through a typical American town and the reasons are 4-way stops and traffic lights; stop, go, stop, go, stop, go. Haven't you guys heard of roundabouts?
Also, slow drivers are a real pain and no doubt cause many an accident. Speed cameras should be used to enforce minimum as well as maximum speeds.
Finally, why all the concern about saving money on petrol (gas)? I see driving fast as a luxury that I'm prepared to pay for.