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Speed Limiters On Semis Show Impressive Safety Benefits

In late March 2012, the Federal Motor Carrier Safety Administration, part of the U.S. Department of Transportation, announced study findings important for the future of commercial trucking safety. Extensive research showed that installing speed limiters, also called SLs or speed governors, on large commercial trucks provides a “profound safety benefit.”

Profound indeed – the study concluded that such devices reportedly reduce crash rates by half.

An SL is an electronic device that keeps a truck engine below a programmed speed limit. SLs are already voluntarily used by some trucking companies for safety and to slow down truck wear and tear. All new trucks come equipped with SLs, but the devices are not always turned on.


Speed-limiter devices are supported by the American Trucking Associations, the biggest U.S. trucking-industry trade organization that advocates for trucking interests at the state and federal levels. In fact, the ATA has asked the federal government to order that all large trucks made after 1992 use speed limiters. ATA President Bill Graves calls speed the “single greatest contributor to highway crashes.”

Important Statistics

The study’s summary cites governmental findings that underscore the obvious danger of a multi-ton vehicle hurtling down the highway at excessive speed – defined as either more than the posted speed limit, or too fast for road or weather conditions:

  • In 2009, speeding was a factor in 8 percent of reported semi-truck accidents.
  • In 2006, almost a quarter of all commercial-truck crashes and more than 10 percent of large-truck accidents with passenger vehicles were reported to involve travel speeds unsafe for the conditions.

Sobering. According to, the legal weight limit for an 18-wheeler is 40 tons (with some receiving permits to drive even heavier), compared with the average weight for a car of about 5,000 pounds.

Study Findings

The current study is actually phase two of a larger project. For this phase, the FMCSA called on the American Transportation Research Institute and the Virginia Tech Transportation Institute to carry out the research. One of the main objectives was to “identify SL effects in reducing the severity and frequency of crashes.” Among other things, the study reviewed truck-carrier data from the years 2007 to 2009 involving about 138,000 trucks and more than 15,000 crashes.

Data analysis was careful and complex. Ultimately, the study concluded that “results across analyses indicated a strong, positive safety benefit for SLs.”

Future of Speed Limiters

Speed limiters seem here to stay. Truckers are already voluntarily using them and the results of the federal study would seem to support the possibility of governmental trucking regulations being strengthened to require more SL use. Such a regulatory move is being aggressively pushed by the ATA, the Truckload Carriers Association and safety advocates.

ATA, Road Safe America and trucking carriers filed formal petitions with the National Highway Traffic Safety Administration requesting SL regulations. In early 2011, the NHTSA combined the petitions and announced it would begin the official federal rulemaking process. The agency indicated it was motivated by responses received in a previous request for public comments on the proposal to require SLs in large, commercial trucks. The proposal discussed was to cap the speed of such trucks at 68 mph.

The public comments (almost 4,000) included support from private citizens with experience in truck accidents either personally, or through close relatives and friends, as well as from some trucking companies and road-safety advocates. In addition to safety, another strong reason for SL support is fuel efficiency and environmental impact.

A variety of grounds for challenging the SL-mandate proposal was also included in the comments, especially from independent truckers. Reasons for opposition included the high cost of SL equipment (which the current study disagreed with) and objection to cars being exempt from the requirement.

The agency indicated it would publish a “Notice of Proposed Rulemaking” in 2012, which would begin the extensive and detailed procedures associated with the creation of federal regulations. But whether the rule is actually passed will remain to be seen depending on what happens in the rulemaking process, said the agency.

As of the date of this writing, no rulemaking proposal has been officially issued yet. In the meantime, if you are involved in an accident with a commercial truck, be sure to consult with a personal injury with experience in truck accidents. You will want to be sure your accident is properly investigated and that your rights are preserved.