On a steep downgrade, why must a doubles/triples driver be especially careful with braking?

DOUBLES/TRIPLES ON DOWNGRADES: Multi-trailer combinations on steep downgrades face: greater total weight (more momentum, more heat generated in braking); risk of brake overheating and FADE (loss of braking from heat); potential trailer instability if braking causes the rear trailers to push or swing; PROPER TECHNIQUE: Select a LOW GEAR before starting the descent (don't wait until moving fast); use ENGINE BRAKING as primary speed control; use SNUB braking (firm application to slow ~5 mph below target, then release to let brakes cool, repeat) — avoid continuous brake application which overheats brakes; control speed for the grade, weight, and conditions (heavier = slower); BRAKE BALANCE: All trailers' brakes must be working and properly adjusted (verify in pre-trip); RUNAWAY RISK: Overheated, faded brakes on a heavy multi-trailer combination can lead to a runaway — use runaway ramps if brakes fail; the added weight of multiple trailers generates more heat, making proper downgrade technique even more critical than for a single trailer; smooth snub braking with correct gearing and controlled speed prevents brake fade and maintains control of the long, heavy combination.