Understanding the Line of Sight and its role in Vehicular Accident Investigations

In many vehicular accidents, the forensic engineer is often called in to make expert opinions as to how the line of sight (ie. how well the driver could see the scenario developing ahead) may have contributed to an accident. Of course, the next determination is to what or who caused this line of sight issue. Contributing factors can be either topographic or man-made. Let’s discuss each.

Topographic factors that impede a driver’s line of sight are typically horizontal or vertical. Horizontal translates to a road with left and right turns. A vertical topographic factor results from hills and vallies in the road. Other topographic factors are trees and foliage that may obstruct a driver’s line of sight.

Man made factors result from humans making decisions that affect a driver’s line of sight. Examples are the way roads and highways are designed and how road construction work may temporarily obstruct visibility. When roads/highways were constructed many years ago and opposing lanes are divided by a large wall and there is no median lane to pull off, you can imagine the accidents that occur when a vehicle is traveling at speed around a curving road and encounters a disabled vehicle in its path. Other situations occur when construction workers separate traffic with large jersey cement barriers which influence the visibility.

Forensic engineers evaluate accidents from a line of sight perspective first by visiting and inspecting the accident scene. Ideally, the engineer will inspect at a time when a similar environment exists as at the time of the accident; lighting and weather can also affect line of sight evaluation. The engineer will work from industry guidelines such as the American Association of State and Highway Transportation Officials (AASHTO) and the Manual for Uniform Traffic Control Devices (MUTCD) to qualify his/her opinions on the human factors involved with designing safe roadways, safe speed (ie. speed limit), and safe working zones.The CED  engineer uses his ‘trained eye’ along with an inspection to capture the evidence and provide the building blocks of accident reconstruction.