Methods for assessing the impact of oncoming glare on driving behavior

Glare from oncoming vehicles while driving at night impairs visibility through the mechanism of scattered light in the eyes, which reduces the luminance contrast of objects in the field of view, and through the mechanism of increasing the visual adaptation level, which decreases visibility following glare exposure. Glare can also cause discomfort, which is most commonly assessed experimentally through the use of subjective rating scales. The present paper reports on an investigation of methods to assess glare's impact on driving behavior in a naturalistic setting. Vehicles belonging to drivers were instrumented with a photosensor to estimate the glare illuminance, as well as sensors for monitoring speed, acceleration, braking status, lane position and other attributes. Data from all of these instruments were collected and stored. Using these data, we investigated whether it was possible to identify relationships between the magnitude of glare illuminance and the presence of behaviors such as changes in speed or lane position. The utility and limitations of these types of methods are also discussed.