Monday, June 29, 2009

Braking News

Knowing that I work in the motor carrier world, friend Pepper Foxpath (not her real name) asked if I would address some things she’s always wondered about commercial trucks. She asked some fabulous questions that I’ll address over the next several postings.

Today’s subject is braking distance. Pepper wanted to know how cars and tractor-trailers compare. I found some stats from the Insurance Institute for Highway Safety that are very interesting. If we look at average total stopping distance at 55 mph, the reaction and braking time for a car and trucks are as follows:

Passenger car -193 feet (2/3 of a football field)
Loaded tractor-trailer with cool brakes -256 feet
Loaded tractor-trailer with hot brakes -430
(twice as long as a car!)
Empty tractor-trailer -249 feet
Tractor only
(driving without a trailer) -243 feet

I’m impressed that a loaded truck’s stopping distance is just 63 feet longer than a car when its brakes are cool. Think about it. The semi and its load weigh 20 times the average 4,000 lb. weight of American cars, minivans and SUVs. That’s some fantastic mechanics! Still, that same truck with hot brakes has a stopping distance 68 percent longer.

Truck brakes heat up as they’re used. That’s why in mountain states, downhill stretches of highway have mandatory pull-offs where trucks sit and cool their brakes.

So when you’re out on the road, how can you tell if a truck has hot brakes? From the driver’s seat of your car, it’s nearly impossible. I think I’ll just drive as if all the trucks around me are steaming hot. No darting in front of trucks or making a last-minute turn into the same lane. Giving trucks the full passing lane as we both descend Missouri’s steep spots. Not braking willy-nilly because I think a truck is tailgating me. Driving smart could keep me from being squashed!

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