You might have heard that you should always leave at least three seconds between your car and the vehicle in front. It might sound like a random number to settle. You may wonder how one number can work in all circumstances from sitting in traffic to flying down the highway.

Why a three-second gap? No driver has instantaneous reactions. There is a time gap between noticing the vehicle in front doing something and your foot applying the brakes or your hands turning the wheel. That is what the three seconds is meant to account for.

It’s easier to count seconds than estimate distance

Road safety experts realized people are poor at judging distance, so giving a minimum following distance would be ineffective. They realized that counting in seconds is relatively simple by contrast. What’s more, by counting seconds, you do not need to think about how fast you are traveling when calculating how far back to stay. Three seconds is generally an appropriate distance in good conditions whatever your speed. As you increase your speed, the distance you travel in those three seconds increases so you’ll need to automatically adjust to give yourself a safe following distance.

Sometimes you need more time

If you are not paying attention, a few seconds may pass before you even notice that the vehicle in front of yours has slowed. The same could apply if you are tired and your reactions slower as a result. Road or weather conditions can also make a standard three seconds inadequate. For example, braking on a piece of road that is wet or slippery will require more distance if you hope to make a controlled stop.

Three seconds is an absolute minimum. If you’re not at your most alert or the weather or surface is less than ideal, then make it longer. Following this rule should reduce the chance you need to claim compensation because of crash-related injuries.