Road Signs and Visibility.

Specifications are established and measurements made for road signs under conditions of lighting and observation close to actual conditions in service. As an example, the conditions of measurement of pavement markings and road signs are described. But the motorist's perception of these signs is not assured by conforming to these requirements alone. The visibility of a sign depends on the brightness of its environment, the observer's visual adaptation (greatly influenced, for example, by the lights of on-coming vehicles) and also on the interaction of all the signs within the motorist's field of vision.