Letter: Briefly

In "Driver blamed for fatal rail crash was on 'risk register'" (27 October) you mention the automatic train protection (ATP) system, which stops trains if they are driven past a red light. It is not installed on our railways because of its enormous cost - more than pounds 400m. The London Underground has used a simple and very effective system of this kind for more than 80 years. What is wrong with that?

Arthur Tarrant

Twickenham, Middlesex