Most people are familiar with the “three-second” rule when it comes to how far behind the vehicle in front of a driver should stay to avoid a crash if that lead vehicle comes to a sudden stop. It’s easy enough to measure by counting to three seconds after that vehicle has passed a specific point like a sign. Your car shouldn’t reach that point for at least three seconds after a lead vehicle has done so.
A number of factors determine how quickly a driver can stop if they need to. Typically, smaller vehicles can stop more quickly than larger ones – all other things being equal.
Size and speed are factors
Consumer Reports has determined that sports cars traveling 60 miles per hour on a dry surface on average need 120 feet to come to a stop. Large SUVs and pick-up trucks need 140 feet. Other types of passenger vehicles fall somewhere in between, with the average being 132 feet. That’s about twice the length of a bowling lane.
Different makes and models of cars perform differently. One Consumer Reports technician noted that hybrids tend to have longer stopping distances because “automakers may compromise some grip for low rolling resistance to help fuel economy.”
Speed is a big factor in how quickly a vehicle can stop. That’s one of just many reasons why it’s not safe to go about the posted speed limit or whatever speed is safe for weather and road conditions (whichever is less).
Braking vs. stopping distance
You may see the terms braking distance and stopping distance used interchangeably from time to time. However, these terms are distinct. Braking distance is how far a vehicle travels after the driver hits the brake. Just how does speed affect braking distance? It’s the square of the speed. That means if the speed is doubled, the braking distance is four times greater. If it’s tripled, it’s nine times greater.
By contrast, stopping distance is how far a vehicle travels after the driver realizes they need to stop and when their foot hits the brake (reaction distance) plus braking distance. Reaction distance can be longer if a driver is distracted or impaired. Both reaction and braking distance (and therefore, total stopping distance) increase with the speed that a car is going.
What’s important to remember is that by traveling at a safe speed, remaining alert and allowing a safe distance from the vehicle ahead of you, you’ll be better able to react to reckless moves by other drivers.
