I do not use case studies to attack, ridicule, or otherwise demean anyone who may have been involved in an actual incident. Instead, I am simply trying to demonstrate the concepts and theories that we have been discussing over the past few months in a real-life environment.
To understand how curve advisory speeds are calculated, we need to understand several issues related to road design. Keep in mind that this article is not meant to be an engineering class. Instead, we will touch on a few keys points and discuss curve advisory speeds in simple terms.
This class reinforces the safety message that no matter how long you have been driving or how “good” a driver you think you are, there are limits to safely operating an emergency apparatus or personal vehicle.
While most of these procedures are justified and useful, some are not. What is common among many of them is the fact that no one knows where they came from. The only background or justification for such a rule is the fact that “an old guy told me to.”
On a slick road, the tires on the fire apparatus may break traction and start to slide before enough lateral g-force is created to cause the vehicle to roll over.
As long as the combined g-force does not exceed the available grip of the road, the vehicle will hold its grip on the road.
While the friction circle is an important aspect of safe driving, it is an often-overlooked aspect of fire apparatus driver training programs.
When the amount of lateral g-force exceeds the rollover threshold of the vehicle, the g-force will “push” the vehicle over. Most fire apparatus have a high center of gravity, and it does not take much lateral g-force to push them over.
Many fire apparatus crashes are the result of the driver drifting off the road and then overcorrecting to regain control of the vehicle. When the driver overcorrects, he turns the wheel and creates an artificial curve in an otherwise straight road.
One of the many ways that lateral g-force can contribute to a rollover crash is by inducing a “weight shift.” It is common to hear driver trainers and crash investigators refer to “weight shift.” But what is “weight shift,” and why is it bad?