One of the critical concepts I learned as a collision investigator this that fully loaded heavy trucks have 50 to 60% of the braking capability of light vehicles. This assumes that the braking system is not overheated, has been maintained properly and is correctly adjusted.
Air brake systems also suffer from brake lag, a short time period that occurs between the driver stepping on the brake pedal and the brakes starting to apply.
These two thoughts ran through my mind when I read a Facebook post from a commercial driver. He had used a frame from his dashcam that showed proper following distance between his front bumper and the back bumper of the pickup truck ahead of him. He had drawn a pink rectangle in this space and advised that he needed every inch of it to stop if something happened to require it.
If that space wasn’t there, whatever was inside it was going to be crushed. Think carefully about that for a moment.
We’ve all been taught to leave at least a two second following distance between us and the vehicle ahead of us when conditions are good. When they are not, we need to leave more space, perhaps adding another second for each factor that departs from the ideal.
Remember that 50 to 60% braking comparison? This means that heavy commercial drivers actually need to follow a four second rule. So do the drivers in front of them!
We should also have been taught that we don’t complete our pass or change lanes unless we can see all of the front of the vehicle behind us in our inside rear view mirror. This may not be enough space when a heavy commercial vehicle is behind you. In fact, if you are too close to the front of a heavy truck, you could become invisible to it’s driver.
The area in front of a commercial vehicle is not the only place that a light vehicle driver needs to worry about. There are a number of other “No Zones” beside and to the rear. Ignoring them could involve you in a squeeze play as this driver in Port Alberni found out.
Constable Tim Schewe (Retired)
DriveSmartBC: Where better than average drivers satisfy their curiosity.