A fresh approach to testing the colour vision of train drivers

Researchers from City St George’s, University of London have described a new two-step approach to testing the colour vision of train drivers in their report Defining Colour Vision Requirements for Train Drivers.

On the basis of the report, the Rail Safety and Standards Board is now urging rail operators and occupational health providers to adopt the new evidence-based approach to assessing colour vision.

The report authors highlighted that the proposed approach would reduce discrimination – as the proportion of people who pass the new testing approach with red/green (RG) colour vision deficiencies increases by more than half.

The new protocol would also result in a three-fold reduction in the severity of colour vision loss among those who pass the test, but still have a colour vision deficiency.

As coloured lights are important for the safe operation of railways, train drivers are required to pass a colour vision test. At present, the Ishihara 24-plate edition is widely used for this assessment.

The City St George’s, University of London researchers propose a two-stage approach. The first stage is a simplified version of the Ishihara test, using the first 13 plates for screening.

Applicants who fail this stage complete a second CAD test, designed by researchers to pass normal trichromats and provide an accurate measurement of the severity of colour vision loss.

Professor John Barbur, of City St George’s, highlighted that the report presents a “step forward” for the rail industry.

“By improving the precision and fairness of colour vision testing, we can ensure safety-critical roles remain accessible to a broader pool of candidates without compromising safety,” he said.

He added that the new approach would reduce variability in the standard applied, and provide a way of quantifying the severity of colour vision loss.

“The new protocol ensures all applicants are assessed consistently, with much reduced variability which leads to enhanced safety and reduced discrimination,” he emphasised.

Dr Rodriguez Carmona, senior lecturer at City St George’s, shared that the research illustrates that it is possible to balance inclusivity with safety in rail recruitment.

“Modernising colour vision testing not only ensures a fairer assessment process for applicants with mild deficiencies but also enhances safety in visually-demanding, colour related tasks,” she said.