Metric confusion

REGARDING the Sandilands tram derailment, why is it that Britain’s modern tram networks do not follow British custom and display speed limits in mph? Speed limit signs in kph display a higher figure, giving passengers in a speeding tram a false sense of security. Was this obvious problem not considered by the RAIB (Rail Accident Investigation Branch)? Mixing measuring systems is never a good idea. In Britain, speeds are thought of in mph and newspaper reports of the Sandilands crash converted the speed limits into mph. Tram speed limits (in mph) could be clearly displayed on signs headed ‘Tram Limit’. Passengers will then have a better notion of permitted speeds and be more likely to act in the case of a speeding tram. Peter G Scott, M.Phil., MIET, CMILT. Higher Denham, Buckinghamshire