The Two Second Rule

Yesterday we started out the day with sunshine. Bright, blinding sunshine. The roads were clear so imagine my surprise when one of our out of district drivers radioed in that traffic was at a dead stop on the highway into the city.

Reports on exactly what happened differ but the gist of it was that a driver hit their brakes when they were suddenly blinded by the sun and somewhere between eight and twenty cars piled up behind them.

This accident was totally preventable. All of the cars that rear-ended the car in front of them violated the two second rule. This rule is vaguely referred to as safe following distance in the driver’s manual. The CDL manual goes further with a mathematical formula that I couldn’t figure out without a calculator.

The two second rule is easy. When you see the rear of the vehicle in front of you pass a tree, sign or other marker start counting one Mississippi, two Mississippi. If you get to the marker before you finish the second Mississippi YOU ARE TOO CLOSE. Simply leave a little more room and try again. This will work at any speed. If you are going 30 mph you will find that you are much closer to the car in front of you than you are at 60 mph. I have found that the average driver is only one second behind the vehicle in front of them which is not enough time.

The number of seconds you need actually varies depending on the length of your vehicle and the weather. For every 10’ of vehicle length allow one second and always round up. So for a car that is between 10’ and 20’ long you need two seconds. My bus is 36’ long so I need four seconds. A tractor trailer needs even more. Add seconds in poor weather.

Give it a try. Most of you will be surprised by just how much space you really should leave.