Yes. Most people assume that a truck can stop as easily as a car. There are several reasons why this is not the case and why trucks pose a much greater safety hazard when it comes to applying its brakes and stopping the vehicle.
First, most trucks travelling on our highways today weigh up to 84,000 pounds. Under the simple laws of physics, (Newton’s first law), “a force put in motion will stay in motion with the same speed and in the same direction unless acted upon by an external force.” What this means is that once you get an 84,000 pound truck moving at a speed of 60-70 m.p.h., it will require a significant external force to slow it down. That is where the trucks brakes come into play.
Like cars, trucks also have brake drums, pads and shoes, connected to the wheel axels. However, unlike brakes on a car which are initiated with brake fluid, which is a hydraulic system, truck brakes are pneumatic, or use compressed air instead of brake fluid as the initiating substance. The truck’s air braking system keeps a steady supply of compressed air, it then directs that air’s flow, and finally, it uses the energy of air pressure and changes it into a mechanical force.
While using air makes the truck brakes extremely reliable because truck brakes never run out of brake fluid like cars do, it also means that there is a brake lag. A brake lag is the time it takes for air to get through the lines and force the brake linings to contact the brake drum. When a truck driver pushes the brake pedal in his truck, he must get used to the fact that the air brakes do not work at once, as they do in a car.
What this means is that a car travelling at 55 mph can stop in about 225 feet with its hydraulic brakes. However, a truck traveling at the same 55 mph speed will take more than 400 feet to stop. Moreover, if the truck has a leak in its approximate 40 feet of hose used for its air brakes, this lag time can be further increased.
Another potential problem with big rigs is downhill braking. Some drivers fail to appreciate the severe demands put on the brakes by long downhill runs. Negotiating a 6% downgrade in elevation for 6 miles is the equivalent of trying to stop the truck from a speed of 238 miles per hour, or 16 stops from 60 miles per hour.
Finally, because most air braking systems do not automatically adjust for wear, they must be well maintained and inspected by the operator. If not, the performance of the air braking system can rapidly deteriorate. In fact, truck inspections demonstrate that a large percentage of trucks have some form of defect in their braking systems. These defects are usually the result of air leaks or poor adjustments.