Speed surveys show that on uncongested motorways, 57 per cent of car drivers exceed the 70mph speed limit, and 20 per cent exceed 80 mph. IAM RoadSmart's most serious concern is that legalising today’s unofficial and tolerated 80 mph speed limit could create tomorrow’s unofficial 90 mph limit. Average traffic speeds would increase, as would accidents and their severity and more people could be killed and seriously injured.