Braking and Stopping with Multiple Trailers
Braking and Stopping with Multiple Trailers
Multiple trailers increase gross weight and the number of articulation points, so stopping distance grows and straight-line stability shrinks. The exam tests smooth brake application, proper use of engine braking, and recognition that trailer brakes must be balanced with tractor brakes.
Core rules
- Increase following distance; a doubles/triples combination needs more room than a single semi.
- Apply brakes early and progressively; avoid hard stab braking that can fold the combination.
- Use engine braking and downshifting before a downgrade; do not ride the service brakes.
- Check that all trailer brakes are working during the pre-trip and after coupling.
- If a trailer starts to skid, release brake pressure to regain rolling traction, then reapply gently.
- Test the emergency line: a breakaway should set the trailer spring brakes.
Worked example
A driver descends a long grade at 55 mph with a triple combination. The service brakes begin to fade because the driver has ridden them for a mile. Correct action: downshift early, use engine braking, and apply brakes in short, firm applications to slow below the safe speed. If fade continues, pull off and let the brakes cool; do not continue.
Traps
- Assuming the tractor's brakes alone can stop the combination.
- Braking hard in a curve, which can cause the rear trailer to swing out.
- Neglecting the dolly brake check.
- Using the trailer hand valve to stop; it is for testing only and can cause a jackknife.