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Diverse Vehicle Sizes

Vehicle size makes a difference in a driver’s ability to see traffic signs at night. The same sign may appear less bright to drivers of SUV s and large trucks than it does to drivers of passenger vehicles.

Larger Vehicles, Different Observation Angles

The number of large trucks registered in the U.S. has increased steadily over the last two decades, reaching almost 11 million in 2009. During that same time, truck traffic (as a percent of vehicle miles traveled) has doubled, nearing 300 billion miles in the U.S. in 2009.¹ The FHWA reports that by 2040, long-haul freight truck traffic in the U.S. is expected to increase dramatically on the National Highway System and may reach 590 million miles per day.² And, unlike automobile and business-truck traffic that peaks between the daytime hours of 7:00 a.m. and 7:00 p.m., long-haul truck traffic has a flat time-of-day distribution, with as many vehicles traveling during nighttime hours as during the day.³
When it comes to seeing traffic signs at night, drivers of large vehicles are at a particular disadvantage because of their observation angle (the measure of separation between a driver’s eyes and his or her headlights) is significantly greater. See Understanding Angularity for more information.
How important is this measure? Large trucks can have twice the observation angle of passenger vehicles at the same distance. That means there’s much less reflected light available for these drivers to see road signs. Drivers of large vehicles can greatly benefit from signs made with high performance reflective sheeting that returns more light in a larger cone of reflectivity.

¹Commercial Motor Vehicle Facts - November 2011, U.S. Department of Transportation
²FHWA-HOP-13-001 - Freight Facts and Figures, 2012
³ FHWA-RD-98-117 - Understanding Traffic Variations by Vehicle Classifications