Protan colour vision deficiency and road accidents.

BACKGROUND: Protans are precluded from holding a commercial driver's licence in Australia because they have a substantially reduced ability to see red lights and have more road accidents involving signal lights. This exclusion has been in place since 1994 but is likely to be abandoned following a current review of medical standards for commercial drivers. This paper reviews the level of risk of road accidents due to protan colour vision deficiency. It also addresses the question of whether it is fair to regard all protans as having a higher risk of road accident because some protans might have a sensitivity to red light that is as good as that of some people with normal colour vision.
METHODS: Data of two studies by Verriest and co-workers are re-analysed to estimate the degree of overlap of the protan and colour normal distributions of sensitivity to red light.
RESULTS: Field trial data show that protans have a very reduced visual range for red signals compared to colour normal observers but there is considerable variability among both classes of observers and the distributions do overlap. However, some variability is due to differences in observers' choices of a detection criterion, their speed of response and the measurement method. A laboratory study of the spectral sensitivity of protan and colour normal subjects that largely removes these sources' variability shows that all protans have a sensitivity to red light that is less than that of the least sensitive colour normal.
CONCLUSION: It is reasonable to conclude that all protans, regardless of the severity of their defect, have a lesser ability to see red signals than colour vision normal observers and for that reason will have a higher risk of road accident.