Brain Reaction Time and Traffic Accidents

Maryland, Virginia, and Washington, D.C.

When you are driving and suddenly encounter a circumstance that may lead to a car accident, you must react quickly and decisively to avoid the accident. There are many components to your reaction, but perhaps the most important is your brain's reaction time to the circumstance. Equally important is the reaction time of other drivers around you to avoid hitting you as you complete your accident-avoidance maneuver. In trying to understand an accident and how liability might be assigned in the accident's aftermath, let's look closely at the role of brain reaction time in a car accident.

What Is Brain Reaction Time?

Many times, people like to lump brain reaction time into one step, from when you see a circumstance to when you act, say by applying the brakes or turning the wheel, but the moment of seeing and reacting is actually composed of several distinct parts. The breakdown we give here is from the 2000 article "How Long Does It Take to Stop?" in Transportation Human Factors by Marc Green.

Mental Processing Time is the time it takes to perceive a circumstance and decide what response to take, the proper reaction time. This time can be broken into:

• Sensation--the time it takes to tell there is something to be aware of in or around the road
• Perception/recognition--the time it takes to recognize what the sensation is, such as brake lights or a pedestrian in the road
• Situational awareness--putting the sensation in the context of driving, such as "will I hit this person/object if I don't respond?"
• Response selection--deciding which of the many possible responses will yield the best results

Movement Time is the time it takes for your body to carry out the selected action

Mechanical Response Time is the time it takes for your car to perform the maneuver, such as braking or steering

How Long Is Brain Reaction Time?

Mechanical response time and movement time are fairly constant, but mental processing time is highly variable. Traditionally, mental processing time, or reaction time, time for a normal driver under good conditions is considered to be about 0.75 seconds. However, recent evaluations have shown that reaction times are more likely to be longer than a full second, and, depending on some factors it may be two seconds or more. Factors influencing reaction time include personal characteristics, intoxication level, alertness, where the eyes are--because most of our visual acuity is directed to recognizing object in the center of our visual field (using foveal, as opposed to peripheral, vision)--how expected the stimulus is, how many different tasks a person is doing at once, and how urgent the stimulus is perceived to be.

Studies have shown that drivers who are intoxicated or distracted are far more likely to be involved in accidents. Driver studies have shown that cell phone use is about equal to intoxication in terms of slowing reaction time and increasing the likelihood of an accident. At least one naturalistic study has shown that eating while driving may be even more dangerous.

Stopping Distances

A car traveling at 65 mph will travel over 70 feet during the estimated 0.75 seconds of processing time. It takes about 0.3 seconds to apply the brake, during which time the car will travel another 28 feet, and actually stopping the car requires another 188 feet with good tires on dry roads. This means that under the best conditions, an alert driver can avoid hitting any obstacle that he perceives when it is at less than 300 feet away. With a brain reaction time of one and a half seconds, the stopping distance increases to over 350 feet. And if reaction time lengthens to two seconds, what some believe is a reasonable estimate of how long it takes for someone to interpret brake lights or turn signals when distracted, the stopping distance increases to over 400 feet. This means that a distracted driver can cause an accident even if following at a responsible 2-second distance (about 200 feet at 65 mph).

The problem becomes even worse if the following vehicle is a large truck, which may require over 250 feet for the brakes to stop the truck once applied, increasing minimum stopping time over 350 feet at 65mph, and stopping distance for a distracted driver becomes almost 500 feet. This makes distraction or any other factor that slows a truck driver's reaction time a critical event in truck accidents. A recent study of commercial vehicle accidents by the Federal Motor Carrier Safety Administration (FMCSA) showed that drivers were engaged in non-driving tasks in 71 percent of crashes.

If you were in an accident caused by a distracted or inattentive driver, the car accident lawyers at Chaikin, Sherman, Cammarata, & Siegel, P.C. can help. Please call or email us today to learn more.

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