Space Cushion Rule
Over the past three years, more than 17% of one insurance carrier’s commercial automobile incidents were related to rear-end crashes, which accounted for nearly 25% of the total incurred dollar loss. According to the Federal Motor Carrier Safety Administration, “each year about 400,000 trucks are involved in motor vehicle crashes. Eighteen percent of the trucks are involved in rear-end crashes…” Not maintaining an adequate space cushion is one common factor that has contributed to this type of crash.
If you leave yourself a space cushion to the front and rear of your vehicle, sudden stops of vehicles ahead will not put you in a dangerous position. You will have room to slow down gradually, which has the added advantage of reducing the possibility of a rear-end collision. Leaving an adequate space cushion also conserves fuel, since you will not be involved in as much energy wasting braking as the traffic tempos fluctuate.
Leave an opening to each side of your vehicle as well. This allows you an escape route and prevents you from being inadvertently trapped if another vehicle should make the wrong move that requires quick evasive action on your part.
Don’t drive alongside of other vehicles in a “static” pattern. You may often see vehicles riding alongside one another, when they are not passing or being passed, and blocking the road for other vehicles. If you are not passing or being passed, control your position – even in heavy traffic – so you are not abreast of another vehicle. This allows you an escape route to either side if evasive action is required. Pulling ahead or dropping back a few feet is easy and may provide you with essential space to maneuver if something does happen. It also allows other traffic to continue to move freely without being obstructed by this bottleneck.
Allow more space than the old rule of one vehicle length for every 10 miles per hour. This rule is inadequate under most conditions and is very difficult to apply.
Space Cushion Rule
Vehicle Time Interval
Car/Van 3 Seconds
Truck/Bus 4 Seconds
Tractor Trailer 5 Seconds
Add one second for over 40 mph –
Add at least one second for slippery road conditions
Federal Motor Carrier Safety Administration – Rear-end Large Truck Crashes
Hartford Loss Control Loss Analysis Data & Process – Hartford Loss Control Driver Letter