What's New in Research T rain movement on North American railways is primarily governed by wayside signal lights.
Information is coded by using various combinations of red, yellow, and green signal lights.
Engineers are required to identify these lights at viewing distances between 0.5 to 1.5 km. Obviously, this task can be problematic for individuals with a congenital color vision defect. For the past 150 years, however, the challenge has been to find an appropriate test which provides a fair functional assessment of the employee's color vision capabilities while ensuring safety concerns are addressed. In the last half of the 1800s and early 1900s, the Holmgren Wool test was the standard test for most rail companies. However, there was also the realization that this test may not be sufficient.