Case of the Month – Auto/Pedestrian Accident

Nov 1, 2017 by

Imagine you are driving in stop and go traffic. It is night. You have two other lanes to your right, and a left hand turn lane on your left. Traffic comes to a stop. Then it begins to creep forward and then it stops again. Then it slowly starts rolling again. Then all lanes come to a stop again. You have been patiently waiting to approach the next traffic light, where you will turn left. While all traffic is stopped, you slowly edge into the empty left turn lane, taking care not to pull into the path of an overtaking vehicle already in the left turn lane.

You slowly increase your speed to about 15 mph. All of the sudden, a man steps out from between the stopped cars on your right directly into your path. You hit him. Is it your fault?

This is what happened to our client’s insured. GEI was tasked to answer the question, “Whose fault was it?” Could the driver have prevented the accident?

The general topic of an analysis of pedestrian/vehicle accidents can be separated into several sections.

The initial section is the perception period. The first part is a measure of the amount of time that it takes for the driver to notice that there is something (or anything) present in the roadway. While we typically assume that the driver has his eyes on the road 100% of the time, generally that isn’t very accurate. The driver may occasionally be looking in the side and rear view mirrors. The driver occasionally drops his vision onto the instrument panel or at the radio. The driver may be sweeping the roadway back or forth with their eyes and then stay focused on a blinking turn signal of that box truck ahead, wondering if it is going to move out of the lane. The time it takes for the driver to perceive that there is something in the roadway varies considerably due to these effects. Additionally, drivers are pretty good at detecting movement, but not so good at detecting changes. Was that round stationary figure on the right shoulder there three seconds ago? Maybe.

Next is the analysis and categorization of what we are looking at, once we are aware that something is there. Is that dark thing a person? Is it a bicycle? Is it a tree branch? Is it a black cow or is it smoke from a campfire? The more visual cues we get, the faster we can identify an object. Shape, color, outline, and contrast are necessary to help us understand what we perceive. Unexpected shapes can play a large part in delaying identification.

The next phase is the period of time spent deciding what to do: swerve, brake, or accelerate? This is a pretty short length of time for most experienced drivers, but throw in the unexpected, and decision paralysis can occur.

The next section is the reaction period. This has two components. The first is the time it takes for the foot to lift from the accelerator pedal and press onto the brake pedal. The second is the time it takes the vehicle to come to a stop after the driver reaches full pressure on the brake pedal. This is also dependent upon many factors. The condition of the tires and brakes and the coefficient of friction of the roadway are the most important (new tires and fresh asphalt versus bald tires and black ice).

The accident reconstruction community has performed thousands of scientifically rigorous research studies and projects related to these factors and has established guidelines of what to expect in these situations.

For this case, our expert reviewed the documentation provided by the client, which included a description of the collision and the police report.

The pedestrian was crossing a 4-lane roadway in an area without a crosswalk. There were three through lanes and a left hand turn lane. The traffic in the three through lanes was stop and go and the pedestrian was crossing between stopped vehicles. The left turn lane was open, and the insured driver was driving in that lane at 15 mph. The pedestrian was relatively short in stature and presumably could not be seen over the top of the stopped vehicles in the right lanes.

A commonly agreed upon daytime perception/reaction time is 1.5 seconds, half to perceive the danger and half to react to this danger. This perception/reaction time has been a standard used in accident reconstructions for many years. Slide or skid-to-stop formulas use a friction factor for the roadway of this type at generally .65 to .75 g. Due to antilock braking of this particular vehicle, this factor can be increased to a friction factor of .9 g. This would indicate a very hard braking stop with antilock brakes. Using the 1.5 seconds perception/reaction time, the driver would travel 33 feet during perception/reaction. Once the driver reacted to the danger and applied the brakes, it would have taken about 8 feet and .75 seconds to stop. This adds up to 41 feet total distance to stop and 2.25 seconds to do so. This assumes a daytime accident.

There are many studies with differing types of collisions that show nighttime perception/reaction times to be considerably longer. In this case the expert used a 2.5 second night perception/reaction time. The time and distance of the stopping remained the same, 8 feet and .75 seconds. The longer perception/reaction time would equal a distance of 55 feet of travel during perception/reaction, totaling 63 feet and 3.25 seconds to complete stop.

In summary, given the facts presented in this case, there was no way for the driver to have avoided the accident. It was not her fault. The client was also pleased to receive his rush report the next day.

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