Sir – Chris Osman (Letters, September 10) is absolutely right about the problems drivers face in trying to see road signs in urban settings. Oxford needs to adopt the tactic used in Portsmouth (the first city to adopt the 20mph limits) where every road subject to 20mph has a very large sign to this effect painted on the road surface as one turns into it. Drivers cannot fail to see these signs as they drive over them and it is safer than taking their eye off the road to look for restrictions.

Liz Grosvenor, Headington