Speed Limiters: The Controversy of Speed Differentials Between Trucks & Cars

The DOT recently published a proposed rule to require “speed limiters” on trucks — meaning there would be technology on trucks to limit how fast they could run. There is, of course, controversy about this proposed safety measure.

See the proposed rule (NPRM) at this link: U.S. DOT Proposes Speed Limiters For Large Commercial Vehicles

The American Trucking Associations (ATA) supports it. Some major trucking companies already use them.

The Owner-Operator Independent Drivers Association (OOIDA) opposes it:  Among the various concerns the organization has are the possibility that truckers will speed more often in low-speed areas, such as construction zones, to make up time, and the potential for drivers to lose money because they couldn’t drive as many miles in a day. http://ht.ly/e2Hy303DTS0

According to Joel Stocksdale, Autoblog,

NHTSA’s proposal says vehicles with a gross vehicle weight rating of 26,000 pounds or more must be limited to 60, 65 or 68 mph. This would apply to both semi-trucks and buses. NHTSA explains that the amount of force a truck will exert in a crash goes up far more drastically than with cars because of the vehicle’s great mass; hence, a lower speed limit with more seriously impact safety. US Transportation Secretary Anthony Foxx summed it up saying, “This is basic physics.” The organization also said that requiring limiters could also save over $1 billion in fuel each year.

I have corresponded with one independent truck owner-operator, Jeff Halling (and Linda, his wife–a truck driver team), about this safety issue (among others). This is what he says,

  • Personally Linda and I think this is a terrible idea. Not because we want to drive 80 miles an hour but because it totally eliminates our advantage of getting out of a situation if we have to speed up a little bit. Every credible study that has ever been conducted says traffic flows better when everyone is running the same speed. Several states have actually increased the truck speed to coincide with that of cars. Illinois and Arkansas being the most recent. Folks driving cars generally drive anywhere from 5 to 10 to 15 miles an hour above the posted limit. Trucks stuck at 65 will create major rear-end hazards. Not to mention the incredible traffic jams and road rages that will increase dramatically. The only way speed limiters will work is if all vehicles have them and we both know that’ll never happen. Very interested to see what the report says this week.
  • Can you imagine how this will affect the Move Over Law. I’m running down the interstate stuck at 65 cars are running 80 and 85 miles an hour. An emergency vehicle is on the shoulder in front of me what do I do. If I move over it’s guaranteed rear-end crash. If I slow down to 40 miles an hour which is what they recommend another possibility of rear-end crash. Just not a good idea.
  • I can say this though. If this law does pass we definitely need to get stronger rear end guards on trailers. Because rear-end crashes will go up ten fold.

Jeff and his wife (they are a trucking team) recently had a good conversation, about truck safety concerns, with an Idaho DOT vehicle inspector while they were being inspected. This is what he told them:

  • While we never touched on the subject of speed limiters he did say he did not like speed differentials. Although we got the impression he wanted to lower the limit for cars not raise it for trucks. Makes sense everybody drives too damn fast.

In fact, I found a September 2004 Federal Highway Administration (FHWA) article on research related to this topic: The Safety Impacts of Differential Speed Limits on Rural Interstate Highways . They study the impact of Uniform Speed Limits (USL) and Differential Speed Limits (DSDL). Here are a couple of quotes from that article:

  • A 1974 study by Hall and Dickinson showed that speed differences contributed to crashes, primarily rear end and lane change collisions.
  • Table 1 shows that a higher proportion of car-into-truck and truck-into-car crashes occurred in USL States, except for rear end crashes where more car-into truck collisions happened in the DSL group.
  • A study by Garber and Gadiraju conducted in 1991 compared crash rates in the adjacent States of Virginia (DSL) and West Virginia (USL).(3) The increase in the posted speed limit for trucks to 105 km/h (65 mi/h) did not result in a significant increase in fatal, injury, and overall accident rates. There was, however, some evidence that the DSL may increase some types of crash rates while reducing others.

It will be some time before every car is equipped with crash avoidance technology, so cars rear-ending trucks will continue to be a problem and underride deaths will still be a problem until the underride regulation is drastically improved.

And, even with the crash avoidance technology, what will be the result of high speed differentials? Will the cars truly avoid colliding with the truck? Will the trucking industry be required to protect against underride at higher speed collisions than what is currently proposed: 35 mph?

Here is a previous post which I wrote on speed limiters last spring:

See why truckers oppose Speed Limiters & why others promote them #VisionZero strategy needed

How is it that I, as a self-made (Ha! like I had a choice) safety advocate, am waffling on this purported safety measure? Do these things ever get a truly comprehensive discussion around the table?

Talkin together

Yet one more traffic safety issue which could perhaps be more effectively negotiated with the help of a National Traffic Safety Ombudsman. . . just sayin’.

UPDATE, February 26, 2017:

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