Kevin Balke, a research engineer at the Texas A&M University Transportation Institute, says that while smart lights can be particularly beneficial for some cities, others are so jammed that only a sharp reduction in the number of cars on the road will make a meaningful difference.

Research from the Virginia Tech Transportation Institute shows that motorists who text face a 23 times greater risk of crash or near crash.

In 2007 its congested roads cost the country 4.2 billion working hours and 10.6 billion litres of wasted petrol, according to the Texas Transportation Institute.