Reaction Time

While driving if confronted with an emergency scenario, the driver’s reaction time can be the difference between success and failure. Although it is an important part of driving and driver training reaction time is not easy to demonstrate. But there are exercises that can show the affect of reaction time on the decision making process.

The Reaction Time Process

There are many factors that can affect the driver’s reaction time, but before we talk about them, let’s find out just what reaction time is.

Reaction time is the sum of the time needed for:

1. The brain to receive information from the senses. The senses we’re referring to also include sensations of motion and related “seat of the pants” sensations.

2. Making decisions on what to do next. Many times, this is a reflexive reaction that carries a potential for danger with it, such as immediately smashing down on the brake pedal when we feel the car begin to skid.

3. Transmission of the messages from the brain to the muscles needed to react and move the controls.

4. The muscles to respond.

The most critical portion of the reaction process is Step #2. After the senses detect the danger, a decision has to be made about what to do with the received information. The time proven example of the inter action between steps 2 and 3 are young drivers. They have very fast reflexes, Step 3, but it is preceded by the wrong decision Step 2. They can react fast (Step 2) but unfortunately they make the wrong decision, and they do it quickly.

Surprise vs. Reaction Time

The best research done on the affects of surprise on reaction time is by Dr. Marc Green. He has been studying the concept of reaction time for over 34 years. If you are running a driver training program I would strongly suggest you read his work – just Google his name and you will get many articles written by the Doctor. In one of his articles he discusses the difference between reaction time when the event is expected, (which could relate to an experience driver) and when the event is a surprise (which could relate to an inexperience driver).

As an example, when the driver knows they have to brake they can achieve the best possible reaction time. Dr Green says that the best estimate is 0.7 second. Of this, 0.5 is perception and 0.2 is movement, the time required to release the accelerator and to depress the brake pedal.

When the need to brake is a complete surprise reaction time is substantially different. In this case Dr. Green suggests that the best estimate is 1.5 seconds for something that may be coming at you from the side and a few tenths of a second faster for straight-ahead obstacles. Surprise creates a perception time of 1.2 seconds and a movement time of 0.3 second.

The Numbers

As many of the articles in the past have mentioned, an emergency is a time distance relationship. How much time does the drive have and how much distance does the driver have. If the decision making process eats up a big chunk of time nothing good is going to happen.

As an example – If the driver is moving at 40 MPH (58.8 Ft/Sec) and is driving into an exercises where they expect to use the brake, the distance used up in reacting to the exercises would be .7 times 58.8 feet or 41.3 feet.

Same speed the driver is surprised and then reacts at 40 MPH (58.8 FT/Sec) the distance used up would be 1.5 times 58.8 feet or 88.2 Ft.

Lesson Learned

A little as .2 seconds more time to react makes the difference between success and failure. By the way what is .2 seconds, .2 seconds is the time it takes to blink your eye. In the blink of an eye you can change failure into success.

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