 In 2017, in the UK, 66% of cars and Light Commercial Vehicles, and 60% of motorcycles left the recommended two-second gap between themselves and other vehicles..

Headway spacing is selected by various safety criteria, but the basic concept remains the same – leave enough time for the vehicle to safely stop behind the vehicle in front of it.The "safely stop" criterion has a non-obvious solution, however; if a vehicle follows immediately behind the one in front, the vehicle in front simply cannot stop quickly enough to damage the vehicle behind it.An example would be a conventional train, where the vehicles are held together and have only a few millimetres of "play" in the couplings.