Monday, March 9, 2009

Sharing the Road with Big Rigs - Braking Distance

One of the dumbest maneuvers I see in traffic is that of small cars cutting off big rigs. This move is plain out idiotic, not to mention dangerous.

A fully loaded big rig can weigh up to 80,000 lbs. Your car weighs in at about 3000lbs, maybe more, depending on the vehicle. We don’t have to be geniuses to see that the difference in weight here is huge and will severely impact the way a big rig reacts on the road as opposed to a regular car.

One difference that everyone should be aware of, is the braking distance. A loaded big rig requires 20-40% extra stopping distance than that of a car, a the percentage that increases with bad weather conditions such as rain and snow. And an empty big rig actually takes even longer to stop than a loaded one.
Some information I’ve come across regarding braking distance states that at 60mph, it takes a big rig 450 feet to stop.
I don’t believe that this estimate includes all the factors that are involved in stopping a car in moving traffic, which in addition to actual brake time also includes perception time and reaction time. When combining these factors with the weight and the length of the vehicle, the total time it takes a big rig to stop at 60 mph comes out to 626 feet, which is the length of over more than 2 football fields.

This is how the math is done:
A big rig at 60mph will cover 88 feet of freeway per second.
Perception Time: The amount of time it takes from the moment a driver sees a hazard in the road to the time the brain recognizes the hazard is about 1 second, which we now know is 88 feet.
Reaction Time: Then we need to allow some time for the brain to signal the foot to step on the brake pedal, and this takes another second…or another 88 feet.
Braking Distance: Now we have a total calculation of 176 feet before the brakes are even engaged, and once you add the 450 feet it will take the rig to stop, you end up with … 626 feet.

This is the minimum distance. This number increases drastically on wet asphalt, and even more so if there is ice and snow on the road. The condition of the driver should also be taken into consideration. A driver may be tired, sick or distracted in some way, which means his or her reaction and perception time will increase.

The braking distance for a truck hauling an empty trailer is even longer! This is due to the fact that when a trailer is heavily loaded, it provides the tires with extra traction, which shortens the retardation time for the vehicle. The braking system on a big rig, as well as tires, springs and shock absorbers, are designed so they work better when a truck is loaded. Once a truck has been emptied, the loss of the extra weight means losing traction and it’s more likely to bounce and lock up the wheels, moving the vehicle into a skid.

And really…. This isn’t like being hit on the bumper by a Prius for a Honda Civic, which is something you would in fact feel and that may cause a whiplash or a broken arm. This is being hit on the bumper by a 80000 lbs big rig, in which the possibility of this interaction being fatal is really high. I think I quoted this number before, but I’ll say it again: 78% of accidents involving a small car vs a big rig ends up being a fatality!

Most truck drivers are safe, reliable and experienced on the road, but unpredictable incidents on the road are many and can throw even the most experienced driver off balance. Leave room for the big rigs.

So play nice out there and stop playing with fate!


Neil Lang said...

happens to me everyday
I call them suicide attempts

Neil Lang said...

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