Two critical components help drivers see traffic signs at night: headlights, which illuminate objects in the vehicle’s surrounding environment, and retroreflective signs, which return the light from the headlights back to the driver’s eyes. Without headlights and retroreflective signs, it would be impossible for drivers to see signs at night and interpret their messages with enough time to react.
Retroreflective materials — like the materials used for traffic signs — are designed to reflect light back to drivers. However, when low-beam headlights direct more light at the road, that means they’re directing less light at road signs. Less light results in less retroreflection and reduced sign visibility, particularly for signs in common overhead and shoulder locations.
Recent studies, however, show that the low-beam headlights of newer vehicles deliver lower light levels to typical traffic signs. The University of Michigan Transportation Research Institute (UMTRI) gathered headlight luminous intensity data from headlights installed in 2019 model year vehicles and compared it to a similar study it conducted in 2011.
The research (PDF, 371 KB) specifically looked at how much light a variety of average LED and tungsten halogen (TH) vehicle headlights emitted. They found that low-beam headlights on 2019 vehicles delivered, on average, 20% less sign illumination than their 2011 counterparts. These new low-beam headlights were developed to direct more light at the road, be less glaring and reduce distractions for other drivers. As a consequence, they also deliver less light to overhead road signs and shoulder signs.
To counteract the lower light levels of modern low-beam headlights, we need to think about ways we can increase the retroreflectivity of the signs themselves. That’s where a more efficient retroreflective sign sheeting — ASTM Type XI — can play an important role. 3M™ Diamond Grade™ DG³ Reflective Sheeting, a full-cube Type XI sheeting, uses 100% efficient full-cube prismatic technology to reflect almost 60% of available light back to motorists — nearly double the level of the next highest class of sheeting.
Type XI sign sheeting reflects more light to compensate for modern low-beam headlights, appears brighter from greater distances and returns light in a wider retroreflective cone to help increase the visibility of overhead traffic signs and signs on the shoulders of the road.
Vehicles are always evolving. To keep building safe roads and adapting to the future, our roadway infrastructure needs to keep pace. Type XI sign sheeting is a vital part of this process.
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