Heavy Truck Safety: Stability, Roof Strength and Crashworthiness

What is a heavy truck?  A heavy truck is precisely what the name implies: a large truck, normally used for long-haul purposes and often in a semi-trailer configuration, responsible for transporting goods across the U.S.  These large vehicles have gross vehicle weight ratings in excess of 25,000 pounds.  When paired with a trailer and cargo, the weight is even greater.  Heavy trucks are commonly referred to as “18-wheelers,” “tractor-trailers,” “big rigs” and “semis.”

When these massive vehicles experience a loss of control they commonly rollover.  When these vehicles rollover, cab occupants are exposed to significant dangers from the weak cab structure of these heavy truck vehicles.  The flimsy cab typically crushes in on the occupants, causing severe injuries and death.

Have you or a loved one been involved in a rollover involving a heavy truck?
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Lack of Stability & Rollover

sm_truck1Heavy trucks have a troubled history when it comes to both vehicle stability and overall durability.  While these enormous vehicles are presumed to be “safe” and “durable” because of their massive size and weight, it is widely acknowledged (both inside and outside of the heavy truck industry) that these vehicles are notoriously unstable and lack adequate protective features to keep occupants safe in rollover events.  A rollover event normally occurs after the heavy truck has lost control.  According to researchers at the University of Michigan Transportation Research Institute (UMTRI) and the National Highway Traffic Safety Administration (NHTSA), loss of control in heavy trucks and rollovers are a major cause of fatalities and traffic tie-ups, “resulting in millions of dollars of lost productivity and excess energy consumption each year.”

Beyond the “lost productivity” and “excess energy consumption,” however, is the danger imposed on heavy truck occupants, such as the driver.  Rollovers of heavy trucks account for more than fifty percent (50%) of ALL truck occupant fatalities in the United States.  In other words, heavy truck rollovers have statistically proven to be extremely dangerous and deadly for heavy truck occupants. This disproportionately high fatality rate for heavy truck rollovers should signal to manufacturers that a significant problem exists.  Yet, little is being done to improve heavy truck design in order to provide occupants with a safer cab.

There is little dispute that the lack of occupant protection in heavy trucks contributes to the fatalities and serious injuries of cab occupants.  Flimsy roofs and the overall lack of cab safety features combine to make heavy trucks very dangerous vehicles when they overturn.  Present cab construction in most heavy truck cabs provide insufficient structural integrity to withstand the anticipated forces present in a rollover event.

While there are many regulations imposed on manufacturers of passenger vehicles – including regulations concerning roof strength in passenger vehicles – the heavy truck industry is less rigorously regulated and lacks the proper oversight and self-governing ability necessary to ensure that heavy trucks are manufactured to protect occupants.  There seems to be little disagreement that understanding the interactions of vehicle payload, tires, suspensions, vehicle types, vehicle stiffness (tractor and trailer, individually and in combination), and roadway surfaces/tire interface on truck rollover events could contribute significantly to improving heavy truck safety. Achieving this level of understanding could be applied to support the design and evaluation of new technologies such as wider axles, wider single tires, adaptive suspension systems, rollover warning systems, ESC/RSC, etc.  Yet, in spite of this potential for design improvements and learning more about the dynamics of rollover incidents, manufacturers do very little “real world” testing to verify the safety of their heavy trucks.

The Trailer

sm_truck3Heavy trucks typically pull trailers.  Trailers can take a variety of forms: tank trailers; flatbed trailers; freight trailers (including refrigerated trailers); tilt trailers; utility trailers; dump body trailers; bulk commodity trailers; bottom or side dump trailers; auto hauler trailers; livestock trailers; logging trailers; and, pole trailers.  In order to better understand vehicle and rollover dynamics, it is important to appreciate the possible role of the trailer in causing loss of control in rollover incidents.  In fact, recent studies have prompted the Federal Motor Carrier Safety Administration (FMCSA) to identify the need to study trailers and tankers, from design through operation, to improve roll stability.

The unique characteristics of heavy trucks – their size, weight distribution, articulation, and varying types of freight carried – make them particularly susceptible to single-vehicle crashes due to rollover and jackknife. In their analysis of fatal heavy truck crash statistics, Moonesinghe et al. (2003, 41) found that a speed limit of 55 mph or higher, poor road conditions due to weather, and road curvature significantly increase the chance for rollover and jackknife, yet there is a converse relationship between harmful events and the size and weight of the truck and trailer. Their analysis shows that the heavier the truck and cargo, the more prone the truck is to rollover, but that the weight serves as a deterrent for jackknife. On the other hand, the odds for jackknife increase with the increase in the length of the truck and trailer (from a single to a double or triple trailer), while the odds for rollover decrease.

Certain safety design changes have been developed and – for some manufacturers – implemented in trailers in an effort to minimize the effect the trailer has in causing loss of control and rollover events.  Specifically, changes to the trailer suspension, use of electronic stability control systems (ESC), rollover stability control systems (RSC) and yaw stability control systems (YSC) have become more prevalent within both the trailer and heavy truck manufacturing industries.   In fact, testing involving the combination of these safety modifications have produced promising results leading to the substantial reduction of crashes.  ESC, RSC and YSC are devices which, when installed on trailers, help the drive to maintain stable control of the vehicle and prevent loss of control events.  These technologies have been available in North America since about 2002 for heavy trucks and trailers.

Conceptually, these technologies (ESC, RSC and YSC) slow the vehicle when the vehicle is in danger of rolling over due to excess speed. Roll stability aids are incorporated into the existing braking equipment on heavy vehicles, so their costs are relatively low. They add several hundred to a thousand dollars to the price of a tractor or trailer and require only minimal additional training of drivers or mechanics. Interestingly, these systems can be quite effective.   Computer simulations demonstrate that electronic stability aids are certainly an important part of an overall rollover prevention program in heavy trucks.

You might ask yourself: “Why aren’t more trailers and heavy trucks equipped with safety features that might prevent loss of control?”  The simple answer is that manufacturers are not required by any law or rule to do so.  Absent these laws and regulations, trailer manufacturers have not shown much initiative to test and implement stability control mechanisms in their trailers.  Moreover, the coordination between heavy truck manufacturers and trailer manufacturers is practically non-existent.  Given this indifference, loss of control remains common in heavy trucks.  Loss of control leads to an increased risk of rollovers, and rollovers expose the weaknesses of these heavy truck cabs.

Have you or a loved one been involved in a rollover involving a heavy truck?
Contact us today to learn your rights.

Contact Us Today