From Mr Kenneth Billings

Sir: Adrian Turner (letter, 26 February) should consult his copy of the Highway Code if he has any doubts about the meaning of twin red flashing lights. The signals are installed wherever their operation is intermittent: at railway crossings, outside fire and ambulance stations, swing bridges and the like. They are also provided on motorways and on police vehicles to signal an immediate stop. The purpose of twin flashing signals is to draw attention where the driver would not expect to be stopped.

Ordinary three-aspect (red, amber, green) signals are only used where the operation of the signals is regular. To use these at level crossings would mean that the green signal would be almost permanently on. There would be problems of familiarity and the lamp would need frequent replacement.

Yours faithfully,

Kenneth Billings

Crowborough, East Sussex