One Point Five Seconds? Accident Reconstruction Truth

A car is going to make a left hand turn in front of you. How much time will you really have? Are you going to survive, or will you be toast? What happens, second by second, to determine who makes it, and who gets hurt? We know that time, speed, and distance are all involved, but how do things really happen?

Most law-enforcement investigators and accident reconstructionists who are not trained in motorcycle accidents make a simple analysis based on the assumption that it takes the rider .75 seconds to perceive the danger, and another .75 seconds to react, for a total of 1.5 seconds. At the end of that period, the rider starts to brake (and/or steer), and the reconstructionist uses formulae to determine how much time, speed, and distance would elapse before impact. Since the rule of thumb is that feet per second is about 1.5 times the speed in mph, this is a simple and convenient way to figure out what happened.

For example, if the motorcycle is going 30 miles per hour, it travels at 45 feet per second. Once the left-hand turn starts, the rider takes 1.5 seconds to perceive and react, so he travels about 67.5 feet before he begins to brake.

Simple, elegant, easy to use. Unfortunately, also completely wrong.

These shopworn estimates of perception and reaction time come from experiments done long ago, using simulators with a fake steering wheel, accelerator and brake. When the light goes from green to red, the subject moves their foot from the accelerator to the brake, and a timer records the result; not very realistic.

Let’s try again, and see what you are faced with in a real accident.

Your perception time includes the time it takes to see, the time it takes to focus attention, and decision time. Only then can you begin to react, and only when your reaction is complete and you do something will your motorcycle begin braking or swerving. The whole time, you are moving towards disaster.

You’re not expecting an accident. You’re cruising along, enjoying the ride, as you approach an intersection. There’s an oncoming car in the left-turn pocket, but you expect it to wait for the light. As you get closer, you notice that the car is slowly pulling forward. You figure it’s just pulling closer to the line. You keep going, but pay a little more attention to the car. Now you are closer to the intersection. The car gets closer to the line, then over it, and accelerates into the intersection. At this point, you have to make sense of a complex and confusing set of facts, one that is contrary to your expectations, and you are beginning to panic. It takes time for your brain to understand what is going on, calculate the trajectory of the car, and deal with the danger.

It doesn’t take a scientist to realize that the perception of this set of circumstances is confusing, and it is going to take you longer than reacting to a green light switching to red. Precious time is gone. Studies show that perception and response time is greatly increased by situations that do not initially seem critical. Your motorcycle keeps going forward until you brake or swerve.

Included in “perception time” is the concept of attention. It took time for you to take attention from the tasks of riding and transfer attention to the task of tracking the now-dangerous left-turning vehicle, and analyze evasive options.

Attention is something we all agree is critical to accident avoidance. Attention is related to the ability to process information. Studies show the ability to switch focus of attention does not change with age. However, uncertainty about the location of information relevant to a certain task does change with age. This would suggest that older drivers are at a disadvantage in complex and demanding traffic situations. This may be one of the reasons many older drivers drive slowly. Vision, particularly night vision, is worse, and it takes longer to clearly see the situation.

Unfortunately, you’re not done. Included in “perception time,” is “decision” time. In that situation an internal dialogue takes place. How fast is the car going? How fast it is accelerating? Will the driver see and stop? Can I slow enough to go behind? Can I get in front? At what point should I get off the brakes and swerve? How much front brake should I use? How much rear? More time is gone. Your bike keeps going forward. While you sort this out, the car accelerates into the intersection in front of you.

Forget the theoretical 3/4th of a second. More like several seconds have been spent.

Finally, you begin deciding what to do. More time, more distance. Time’s up. You are now way too close to do anything successfully. You are going to hit the side of the car, and go flying over it. Even if you catch a little brake, expect to be six or seven feet in the air as your limbs flail towards a landing more than 20 feet away.

We can talk about things that will help avoid a collision. Covering the front brake can save a small amount of time. Having a foot on the rear brake saves time, but can lead to a skid-induced highside. But we need to stop looking at motorcycle accidents using methods designed for car accidents.

Mike Padway is a motorcycle lawyer with a passion for riding and riding safety. He handles cases throughout the state and can be contacted by email: mike@michaelpadway.com.

This article was originally published in Citybike Magazine.

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