New extentive experiments demonstrated that: (a) protan observers are more deficient than deutan ones with regard to perception distances of some traffic panels, of vehicle red stop lights, of vehicle red rear-position lights and of white, yellow and red reflectors. Contrarily, deutan observers are more deficient than protan ones for the distinction of differently coloured traffic lights and vehicle rear lights; (b) protan and deutan drivers are nevertheless not responsible for more traffic accidents than drivers with normal colour vision; (c) this apparent contradiction is due to psychological compensation mechanisms. The practical conclusions are: (a) that persons with defective colour vision need not to be excluded from non professional road traffic; (b) that it is nevertheless useful that they should be aware of their handicap; (c) that the red traffic signal has to be larger than the other ones; and (d) that the stop and red position lights of vehicles must be sufficiently intense and that the filters transmitting only pure red should be avoided in them.