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Experience:  Retired Civil Engineer, USC Professor & Realtor, financier
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# how long would it take a tractot trailer

### Resolved Question:

how long would it take a tractot trailer combination weighing 80,000lbs to stop going down a 8% grade
Submitted: 9 years ago.
Category: General
Expert:  The Geezer replied 9 years ago.
The exact answer would depend on the condition of the unit's brakes, whether or not the pavement is dry, and whether or not there were any sand or gravel on the road.

You would also have to specify the speed at the time the brakes were applied.

But a reasonable estimate of the stopping distance, using a typical highway speeds, on FLAT ground, would be:

30 mph - 100 feet
60 mph - 426 feet
65 mph - 525 feet

http://www.truck-accident-lawfirm.com/CM/Resources/Trucking-Accidents-Collision.asp

From my Highway Engineering classes at USC many years ago, the increase in stopping distance for such a grade is in the range of 5-10%. This gives the following estimates:

30 mph - 110 feet
60 mph - 450 feet
65 mph - 575 feet

These estimates do NOT include the driver's reaction time, and assume that the brakes have not been overheated by immediately prior overuse.