What is the two-second rule of driving?
In order to adequately stop in time to not smash into the car in front of you in traffic, you need to keep a minimum of a two second ‘space cushion’ of stopping distance between you and the car ahead of you – at 30 mph or less.
To find this distance while driving – eyeball some object on the side of the road, like a billboard sign. After the car ahead of you passes the object, count two seconds. If you pass the object within two seconds, you’re driving too close to the car in front of you. You’ll need to remember to pay attention during these two-second calculations to make sure that other roadside objects, don’t come out of nowhere.
The two-second rule is not sufficient for all speeds. The two seconds between cars is only relevant for cars at the lower speeds. You’ll need a much longer stopping distance when you’re driving faster.
The calculation for the time needed between two cars to allow the trailing car enough distance to come to a complete stop before hitting the leading car that had to stop immediately – is as follows:
Given a braking distance of 57 feet, (according to the Iowa Department of Transportation), when traveling at 30 miles per hour (30 mph = 44 feet/second), you need to have 1.3 seconds between you and the car ahead of you. So, you’ll need 57 feet in order to stop 44 feet/second=1.3 seconds.
But, our brains need time to process the information, decide to brake and then, to signal our feet to slam on the brakes. Using an average reaction time of 0.0000000000475, or 1.5 seconds, (from by the Iowa Department of Transportation), the total time needed to stop is: 1.3 seconds (braking time) + 1.5 seconds (reaction time)=2.8 seconds total.
At 60 mph, the time needed between vehicles comes out to over four seconds.
So why doesn’t the two-second rule work? SCIENCE. The reason is that the energy required to stop is dependent on the force of friction (F) over a distance (x) (W = FΔx) and is also equal to the change in kinetic energy, which is dependent on the mass (m) and speed (v) (ΔKE = ½mv2), which means that FΔx=12mv2.
If we double the speed (v), the distance (x) is quadrupled (22 = 4), meaning more stopping distance is necessary at high speeds than predicted by the two-seconds rule. Here’s a video that might help:
A good approximation would be to add a second to your reaction speed (1.5 seconds), between cars for every 20 mph that you’re driving. That works out to about three seconds for city traffic and four to five seconds of stopping distance for highway traffic. Apply a couple more seconds between cars in order to safely stop if the road is wet or slippery.
If another driver was following too close to you and you’ve been injured as a result of their actions, you may be entitled to compensation. It always depends on circumstances – but, your damages might include:
- Reimbursement for your medical expenses,
- Repair or replacement of your vehicle,
- Compensation for pain and suffering,
- Compensation for lost income.
We Will Fight For You!
Call the Law Office of Gerald Fugit at 432-301-9252.