10.1.2 Evidence of crash risk
The evidence is incomplete regarding visual fields and visual acuity and crash risk.1–3 This is likely due to the many methodological reasons outlined in Part A of this publication (refer particularly to Part A section 1.5 Development and evidence base). The degree to which reduced visual acuity increases the crash risk ranges from 1.17 to 7.6 times. While it is generally agreed that adequate visual fields are important for safe driving, the actual cut-off value that should be set remains unclear.7
The majority of research suggests there is no association between crash risk and colour vision. While there is evidence that people with red-colour-deficient vision have difficulty in detecting red lights and stopping in laboratory and on-road testing, significant improvements in road engineering mean that people with red-colour deficiency may largely compensate for their deficiency while driving.