Sir – I see that, amongst other unsightly signs, Oxford now boasts placards with the words ‘It’s for a reason’ or somesuch. This is, I imagine, the best ill-defined justification of the new 20mph that could be managed.

Driving along Five Mile Drive at 20mph and then Sunderland Avenue at 40mph one is struck by the total pointlessness of the enterprise. Dan Hearn’s article on the danger of such a low limit illustrates one downside. Paul Smith’s quote is surely misleading, suggesting as it does that speed is the only cause. The reduction in impact with a reduction in speed is acknowledged, but first one must have the accident.

Gerard Van Dam, Eynsham