I had the opportunity to attend one of several Rollover Prevention Summits sponsored by the US Department of Transportation (DOT), National Tank Truck Carriers, and Refrigerated Transporter's sister publication, Bulk Transporter. It was an enlightening experience.
Administrator of the Federal Motor Carrier Safety Administration John Hill, in his remarks to the meeting, said some 45 percent of injuries from single large truck accidents are due to rollovers, and that 52 percent of truck occupant fatalities involve a rollover accident.
As you might expect, cargo tank trucks are more likely than van trucks to roll over, often due to drivers not considering the continuous movement of liquid in the tank. Hill noted that 75 percent of all cargo tank truck rollover accidents are caused by driver error, while only 10 percent of rollovers are due to excessive speed. Cargo tank rollovers account for one in four tanker driver fatalities.
What I learned from the many presenters at the summit that most surprised me, is that a driver — whether in a tank or van truck — is seldom aware that his rig is rolling over. A driver usually only feels his truck starting to roll over after it is too late to do anything about it. The truck has reached its “rollover threshold.”
This is the basics of a truck rollover, according to Triodyne, a mechanical engineering consulting firm specializing in safety of engineering systems and mechanical devices: When a truck travels in a curved path, it leans to the outside of the curve because of the centrifugal force acting through the truck's center of gravity. The centrifugal force increases with speed and with the curvature of the road.
The truck's ability to resist rollover is determined by its rollover threshold. This is the lowest value of centrifugal acceleration that causes the truck to tip over when driving steadily in a curved path.
A driver doesn't feel his truck beginning to roll over until after it is too late to respond because there is a delay in the rolling of the tractor. The trailer has a higher center of gravity, and the flexibility of the trailer allows it to twist and start to roll while the tractor's tires maintain contact with the road.
Rollovers can occur when a truck is traveling too fast, especially around a curve. They can take place when a truck is “tripped.” This is when the tires strike something such as a curb or object on the roadway while turning, or when the tires go off of the pavement, or when a truck is returning to the road after drifting off the pavement.
Rollovers also can happen due to abrupt lane changes or sudden road maneuvers.
Driver inattention and/or fatigue also plays a role in rollovers, because a driver may not realize the need to slow down or take evasive action in time to prevent his truck from rolling over.
Then there is the influence of a truck's length, weight, cargo, weight distribution, suspension, center of gravity, and so forth.
While electronic vehicle stability systems, highway design and signage, and automated warning systems can help prevent truck rollovers, the biggest factor is driver behavior and awareness.
The most effective way to avoid a rollover, or any accident for that matter, is for drivers to always drive safely and cautiously. Furthermore, drivers must be aware of the situations that can lead to a rollover.
Remind your drivers to stay alert and anticipate the actions of other drivers. Stress the need to avoid sudden maneuvers, such as swerving quickly to avoid hitting an animal or road obstacle. Emphasize the importance of driving the load, not just the road.
I welcome your thoughts and comments.