Towing Trailers and Converter Dollies
What this domain tests
This domain covers doubles and triples: converter dollies, coupling order, safety chains, air lines, electrical connections, shut-off valves, and the handling differences of multi-trailer combinations.
Core rules
- A converter dolly has its own fifth wheel, axles, brakes, and often a safety chain or chains. Inspect it as a separate vehicle.
- Couple the dolly to the tractor or lead trailer squarely; connect air lines, electrical cord, and safety chains.
- Confirm that dolly brakes and lights work and that air line shut-off valves are in the correct position.
- Multi-trailer sets amplify sway and rearward amplification; drive slower and steer smoothly.
- Backing doubles is difficult; use a spotter and avoid blind-side backing when possible.
Worked example
You hook a second trailer to a dolly but leave the dolly's electrical cord unplugged. The dolly brakes and lights may not function, and the trailer behind it may have no brake lights. The correct action is to connect the cord, check all lights, and test the dolly brakes before moving. The reasoning: every trailer and dolly in the set must have working brakes and lights; a missing connection affects following drivers and stopping performance.
Traps that cost marks
- Forgetting safety chains or leaving them crossed or loose.
- Connecting glad hands incorrectly or leaving shut-off valves closed.
- Skipping the dolly brake and light check.
- Backing a double without a spotter or mirror check.