Although glare is not the number one cause of automobile accidents, it is a prevalent cause. The effect of glare, whether from oncoming headlamps or sunlight, obstructs the driver's vision. It can take an average, middle-aged person's eyes six to seven seconds to adjust to glare from oncoming traffic. If you were traveling down a simple two-lane road at 40 mph. In six to seven seconds, you and your vehicle would have traveled between 354 and 414 feet. In that amount of space and time, serious automobile damage could easily occur.  Vision is also effected by age.  As a person ages, his ability to focus and recover from glare continues to diminish.

Crash data compiled from police-reported crashes (2000-2003) was analyzed by the National Highway Traffic Safety Association (NHTSA). Variables studied were sex, age, travel speed, maneuver, crash hour, flow of traffic, number of lanes, roadway profile, and vehicle role. This data showed a positive correlation with glare - caused by bright sunlight, headlights, or reflected glare. Our National Critical Technology's technical application was purposed to diminish or eliminate these types of dangerous glare.
 

Image courtesy of NHTSA: National Center for Statistics and Analysis

The conclusion of the report states that

what is needed is a common approach to both headlamp and sunlight glare and develop counter measures to reduce glare before it strikes drivers' eyes.

This correlation led to the NHTSA agreeing in 2003-2004 that moderating the glare of headlamps as well as from the sun would greatly reduce the number of traffic altercations caused by high-mounted headlamps on trucks, headlamps with High Intensity Discharge (HID) bulbs and other fog lamps mounted on the front of vehicles. The conclusion was that remedying glare-based visibility issues should become one of its regulatory priorities.

In 2005 over 900 accidents in Kentucky alone were caused by glare. Most state traffic accident reports, including Florida and Washington, have a place on their reports indicating whether or not glare was a significant, contributing factor.