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If we're going to limit vehicles' ability to speed, start with the real problem: Cars

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Updated May 29, 2022

A version of this column by longtime Overdrive Extra contributor Clifford Petersen was sent by the writer to his Congress representatives in Missouri, likewise filed to the regulatory docket the Federal Motor Carrier Safety Administration has opened asking a series of questions around speed-limiting technology. FMCSA extended the comment period this week through July 18. 

Several times over the last couple of decades truckers have expressed concerns on how dangerous differential speed limits, or separate limits for cars and heavy trucks, can be for our nation’s highway users. Yet once again, the Federal Motor Carrier Safety Administration appears to be ignoring its own findings and disregarding the many studies whose results speak to that effect. As Overdrive readers are likely well aware at this point, FMCSA is making moves to to mandate more control over truckers’ businesses and personal safety with a potential rulemaking to require use of speed-limiting technology.

As far back as 1964, studies noted the variance created by different speed limits for cars and trucks increased the likelihood of interaction, resulting in more cars' rear-end collisions with trucks. Up closer to the present day, implementation of differential speed limits on two-lane rural highways were found in 2012 to have correlated with a more than 60% increase in fatal accidents.

Those are but two studies. Others have clearly shown increased accident probability by virtue of the simple fact that two classes of vehicles traveling at differing speed limits will inevitably lead to an increase in overtaking maneuvers, shorter following distances, and more.

An analysis conducted by the Federal Highway Administration division devoted to technology and research in 2004 analyzed the safety impacts of a wide variety of speed-limit policy changes, including shifts to and away from differential speed limits and unified speed limits. Not one single state experienced a significant decrease in crash rates. Yet in states that moved from a unified to a differential speed limit, a fatality became a more likely result for a crash.

In other words, states that changed from a single speed limit for both cars and trucks to a differential speed limit recorded an increase in crashes where fatalities were the result.

This, folks, is simple physics. Newton's third law of motion states that when two objects interact their collision transfers force equal in magnitude and opposite in direction – the proverbial equal and opposite reaction we’ve all been taught. If a car traveling at 75 mph impacts a wall, the sudden decrease in velocity transfers as much force of impact back to the vehicle formerly in motion as it does the wall. 

Personally, I was taught in high school drivers’ ed that when a vehicle impacts an object, occupants in the vehicle not secured by restraints will also impact the object collided, or the roadway, as it were, at the same speed of travel upon impact. As noted, simple physics.

As an over-the-road trucker for nearly 25 years, I observed that the average speed of cars is about 5-15 mph above the posted speed limit. If trucks are limited to 65 mph in a state with a 75 mph speed limit, cars traveling at 75 to 90 mph create a differential of 10 to 25 mph.

This puts the trucker and car occupants themselves at greater risk than otherwise might be the case.

Another lesson in simple physics: if a truck blows a steer tire at 65 mph, the only possible way to maintain some control in the moment is to increase speed two to three mph and slowly guide the truck off the highway. However, if that truck is technologically limited at that speed when the tire blowout happens and cannot increase to a controlling speed, the driver is at the mercy of gravity. If that governed truck blows a left steer tire, it will enter the lanes of oncoming traffic, or the highway median, as the case may be. A right-steer blowout will send the vehicle off of the roadway into a ditch, culvert, tree, embankment, cliff ... with probable roll-over, impact with a stationary object, death. …

The stakes are high.  

[Related: 'Dumbest idea I've ever heard': Owner-operators say not to mandated speed limiters]

As a professional trucker, I set my cruise control at 65 mph. I saved fuel and wear and tear, thus reducing maintenance expense. It’s a business decision, but also a safety decision. Without a governed top speed, I retain the ability to safely overtake and pass a vehicle, if need be, instead of delaying traffic behind me and creating road rage in aggressive drivers by holding them up.

Professional truckers are not the problem. Excessive speeding by automobile operators is. If government is going to limit the ability to speed, start with cars.

While mandated electronic logging devices may well have aided in professionals’ compliance with the hours of service rules, they’ve also raised the stakes when it comes to time. Even a mere 3 mph can mean the difference between a trucker getting home in time for a 34-hour restart and shutting down 50 miles away.

While that may not sound like much, a speed limiter mandate is bound to impact capacity and exasperate the limited parking situation. At the same time, there is currently a proposal to redefine overtime pay as it applies to employee truck drivers. In my view, if that is done, speed-limiter use by truckers will be even less necessary. The few nonprofessional truck drivers who ignore speed limits will see clearly the benefit of slowing down instead of rushing.

My reading of the research suggests a more effective approach to speed limits with a mind toward pushing down accident rates would be implementation of variable speed limits in congested areas – and/or during weather anomalies.

Truckers are already heavily regulated, and far less likely to be at fault in an accident where a passenger vehicle is also involved. If regulation is required, then perhaps you should look at regulating those who are more likely to be at fault.

[Related: One operator's 'hairy' trip speed-limited at 65 mph]  

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