Are traffic signs too bright?

The world is changing, the population is ageing and technology transforms our lives rapidly. What level of traffic sign brightness best satisfies the changing needs – ageing population, different road users and more challenging road conditions?
This paper will look at how bright a traffic sign needs to be to meet the maximum number of road users’ needs. This literary study draws on research from key factors effecting sign brightness:
• Sign condition: How much impact does the cleanliness, age, installation and positioning of a sign effect the clarity of information to a driver?
• Human factors: Marland (1967) found that human vision, perception and reaction time declines with advancing age; around the age of 60, the amount of light reaching the photoreceptors is only 25% of the amount seen at age 20.
• Road users: The proportion and weight of freight traffic on road networks at night is
increasing. Advancing headlight technology is affecting the illumination levels of
retroreflective signs. Truck drivers are disadvantaged when viewing signs at night due
to the large vertical displacement their seating positions have relative to the truck’s
headlights.
• Headlight configuration: There have been significant technological developments in
the design and output of vehicle headlights, as well as the ability to design the light
distribution profile of the headlights, thus directing light into specific areas of the
road-scape.
• Illuminated vs. retroreflective signs: With the increase in LED and illuminated signs
how can the best luminance level for the driver be achieved?