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WINTER WHITEOUTS

(Disorientation Syndrome)

Human factors are in the field of Accident Reconstruction is important when a determination is to be made whether a driver's action(s) in an accident falls within what would be considered to be reasonable or acceptable behaviour.

This article discusses the negative effects of driving under adverse conditions specifically in winter whiteouts, where a phenomenon known as Disorientation Syndrome is known to occur. Unfortunately, limited research has been performed on this topic.

 

Resulting Problems

The problems that result from Disorientation Syndrome are visual and psychological in nature which affect the detection, recognition and identification processes that occur during the driver's decision making.

 

When Do They Occur?

Winter whiteouts occur under daylight conditions. Wind velocity and air turbulence increase the density of loose, dry snow, bringing it up to, and above the driver's eye height. Driving on a highway through open territory, being passed by large vehicles or following or passing snow plows are situations in which winter whiteouts can take place.

 

What Happens?

In a whiteout situation, daylight illumination decreases. A fairly uniform sky and snow covered ground will result in very small luminance differences within the driver's field of view. The situation can be compared to driving in heavy, dense fog.

The driver will have difficulty detecting cues in their peripheral field of view which serve to direct the foveal vision, enabling the acquisition of detailed information. Visibility detection is reduced. Objects that can be seen at all, lose contrast, in that they appear distant.

There can also be a loss of optical guidance leading to a loss of a reference frame (space orientation). The driver no longer has road reference markers to be guided with. They may continue driving straight, hopefully assuming the road will be straight as well, or they may drift toward the centre of the road, to avoid leaving the roadway. Steering becomes more erratic with a shorter preview distance.

 

Visual Demands

The driving task then becomes more demanding. The visual process demand is increased leading to a decrease in peripheral vision performance in terms of reaction time and response eccentricity (functional field of view). More effort is required to acquire and process information regardless of the amount of information that is available. Therefore, a continuous state of stress is produced. Fatigue may become a problem.

In practice, there is little opportunity to learn to drive in adverse conditions.

A detrimental effect of this is that the driver's ability to estimate the speed of his/her own vehicle is impaired. Testing has shown that a vehicle's speed will be maintained until the reduced visibility zone is entered or just about to be entered. Speed reductions of up to 48 km/h were then observed. But, as they proceeded through the zone, they reportedly adjusted to the situation and felt more confident.

 

Expectation of Obstacles

Under adverse weather conditions, a driver's expectation of seeing or encountering obstacles or other vehicles on the roadway is reduced. Therefore, no detection in the visual field will lead to the incorrect assumption that no object or vehicle is there. This is a part of the false confidence that a driver may develop.

 

Overdriving One's Visibility Distance

When nothing can be detected in the visual field, the driver may experience "empty field myopia", fixing his/her sight at a dangerously close distance. This distance is too short from the vehicle to enable the driver to react appropriately, if an object is detected.

In conclusion, drivers subjected to Disorientation Syndrome due to impaired visibility are likely to react by reducing the speed of their vehicle. The demands on the visual system will increase, but the driver will experience a decrease in visual performance, and will probably have reduced obstacle expectations.

 
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Walters Forensic Engineering | 277 Wellington Street West, Suite 800 | Toronto, ON M5V 3H2
Information contact: engineering@waltersforensic.com