Sir – Mark McArthur-Christie may be chairman of the Oxford group of the Institute of Advanced Motorists but his grasp of basic physics seems shaky.

Last week he was quoted as stating “Speed does not kill. Inattention, people not observing properly and people not anticipating properly are what kills”.

That this is nonsense is easily demonstrated by a simple thought experiment: imagine sitting in your car being as inattentive and unobservant as you like, but doing 0mph. Will you kill anyone? No.

Cars kill by converting kinetic energy — proportional to the vehicle’s mass and the square of its speed — into traumatic injuries. In other words, speed is precisely what kills. Vehicle speed may not be the primary cause of most accidents, but in reducing the time available for drivers to react it increases the likelihood of accidents, and by increasing the energy to be dissipated in any collision it is the primary factor in determining their severity.

I agree with Mr McArthur-Christie that improving driver training and skill levels is crucial, but even the most skilled and best trained people have lapses of attention and make errors of judgement. Having a system of routinely enforced speed limits to restrict the potential for harm from those lapses therefore seems to me to be highly desirable.

Richard Stamper, Oxford