Stopping a 70-Foot Long Truck On a Dime

Driving on I-95 today, we passed many semi-trucks (and a few even passed us).  As we passed these 53-foot rigs (that's just the length of the trailer, not the whole tractor-trailer which is closer to 70 feet), I was thinking back on one of my earlier careers where I worked for a time developing anti-skid braking systems for big rigs like the ones we were passing.

In the early 1970's, the Federal Government passed a law that said that heavy trucks (e.g., tractor-trailers, cement carriers, and even school buses) had to be able to stop in a straight line within something like 350 feet from a speed of 60 mph.  While the regulation didn't specify how this was to be done, the only practical way was by using anti-skid (otherwise known as antilock) brakes.  Brake systems like this had long been employed on passenger aircraft and the systems were becoming more common on automobiles.  But antilock brakes were completely new to trucks.  The trucking companies hated the idea.  It would mean that they would have to invest in expensive, new (and as yet unproven) technology.  To save money in those days, lots of trucking companies would take trailers on the road with at least some of the wheels having brakes that were known to be defective.  With the mandate, not only would they have to buy the antilock systems, they would have to actually fix the brakes.  I thought about this often as I was next to a truck on the highway.  I still do.

Nonetheless, the braking requirement was already a law and we set about developing a system that would work on heavy trucks.  I will spare you the gory details except to say that we finally managed to get a system working.  The company that I worked for (Kelsey-Hayes) had a test track that had been an Army Aircorps runway during World War II.  Here I was, a 25-year old engineer, driving a truck that was configured to weigh as much as a fully loaded cement truck, going down a runway at 60 mph.  The truck had been fitted out with our antilock brakes and in the cab next to me were all of these recording instruments to measure various parameters of the braking system while we put it through its paces.

After getting up to speed and making sure everything seemed to be working.  I literally stomped on the brake pedal to see how fast I would stop this monster.  I don't think I can convey what it felt like to be riding in this rig that seemed to actually be hopping down the pavement like some bucking bronco as it shuddered to a halt.  The instruments were banging back and forth against the dash...and so was I.  But the truck stopped in the required distance.  I had to peel my fingers off the steering wheel and sit there for a few moments before I could even look at the test results.

A system like this is never developed in one test or even a hundred tests, but eventually we had a working system.  And what happened?  The trucking companies lobbied the government and had the law rescinded.  Antilock brakes were no longer required and without the legal mandate, there was no market. Our system died.  As far as I know, they are still not required on heavy trucks.

I have driven a lot more miles over the intervening years and I have seen quite a few accidents where trucks have either careened off the road or been involved with multi-vehicle crashes.  I often wonder what might have happened if these trucks had been equipped with antilock brakes?  I know it wouldn't have prevented all these accidents but I believe that it would have helped.  But when the choice for the trucking companies came down to cost or safety, cost won.

From what I read, the NHTSA has had a mandate in place for a number of years which requires a stopping distance from 60 MPH of 335 feet or less.  In 2012, the mandate is going to get even stricter.  Heavy trucks will have to be able to stop in 225 feet.  There is still no explicit requirement for how the technology to meet the requirements but at least the limits are getting tougher.  Who knows?  Maybe a new generation of young engineers will develop the antilock truck brakes that we had attempted to bring to the highway.  I hope so.