Heavy trucks may have hydraulic brakes or air brakes (which require a Z endorsement). Whatever the system, the truck driver must respect how long a loaded vehicle needs to stop.
Total stopping distance is the sum of:
- Perception and reaction distance: how far the truck travels while the driver sees a hazard and responds.
- Braking distance: how far it travels once the brakes are applied.
- For air brakes, add a built-in air-brake lag of up to about half a second before the brakes act.
Two things lengthen the stop sharply:
- Weight: a heavier load increases stopping distance roughly in proportion to the weight.
- Speed: stopping distance grows faster than speed. When speed doubles, braking distance increases about four times.
🧠 Memory hook: "Double the speed, four times the stop." A loaded truck needs a long, early decision, never a last-second one.
Recall: Name the parts that make up total stopping distance. If speed doubles, how does braking distance change?