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Why is Glare an Issue for Drivers?

Nighttime driving is considered more dangerous than daytime driving, as a disproportionate number of fatal accidents occur after dark [1]. This increased danger may be due, in part, to the increased amounts of glare at night. Glare is characterized as, “a sensation caused by bright light in one’s field of view. Glare can reduce one’s ability to see, create feelings of discomfort or both." [2]

In a 2007 Report, the National Highway Traffic Safety Administration summarized existing findings regarding the effects of glare on drivers. When glare presents an issue to the driver, it is referred to as “discomfort glare” [2]. Glare can be an issue for drivers because it causes light scatter in the eyes, reducing seeing distance and the contrast of roadway objects. Glare also increases a driver’s reaction and recovery times. For those reasons, glare may increase the risk of accidents [2].

The following factors increase the risk of discomfort glare occurring or causing an accident:

Driving on a two-lane highway [2]:

• On two-lane highways, oncoming traffic is closer to a driver’s line of sight, producing more scattered light in their eyes from the oncoming vehicles’ headlamps.
• Two-lane highways also tend to have steeper curves and grades, which may potentially expose drivers to a higher range of glare from oncoming vehicles, as opposed to drivers on multi-lane roadways.
• Two-lane highways also tend to have lower light levels and fewer roadway markings, both of which can make the vision impairment from glare more of an issue.

Age [2]:

• As people age, their pupils shrink, causing less light to enter their eyes, causing more light scatter from glare.
• Older people are also already more likely to suffer from vision disorders, such as macular degeneration, diabetic retinopathy, and detached retinas, which can also make glare discomfort worse.

Vehicle Design and Operation Factors [2]:

• Improperly aimed headlamps can increase glare and reduce visibility for drivers.
• Headlamps that are placed too high could result in higher light levels entering the eyes of oncoming drivers, increasing discomfort glare.
• The colour of the headlamps also plays a role in discomfort glare. Prior studies have indicated that people experience greater discomfort when exposed to blue high intensity discharge headlamps than when exposed to yellower, halogen headlamps.
• Drivers whose vehicles have dirty or damaged headlights have reduced forward visibility, due to the dirty/damaged headlights producing lower light levels on the roadway. The dirty/damaged headlights can also increase the light levels being aimed at oncoming traffic.
• Dirty/Damaged windshields can also scatter light and may increase the effects of glare.

Glare and Accident Reconstruction:

A full Accident Reconstruction can determine the likely causes of a motor vehicle accident. At LISKE, our Accident Reconstruction experts complete a thorough forensic investigation of the available records and physical evidence to reconstruct your nighttime driving accident. LISKE’s Accident Reconstruction experts may conduct a Forensic Vehicle Examination and/or Forensic Site Examination to determine what role, if any, glare played in causing the accident. Our unique team approach also allows our Human Factors and Injury Biomechanics experts to provide additional analysis on both accident and injury causation.