CDL Doubles and Triples Practice Test

Question 1

What is the maximum legal length of a doubles combination in most states?

Accepted Answer

65 feet

Answer

Most states allow doubles combinations up to 65 feet in length, though some western states allow longer combinations on approved routes. Triples are limited to certain routes and are regulated by individual state law. Always verify local regulations before operating.

Question 2

When coupling a second trailer to form a doubles combination, the converter dolly should be:

Accepted Answer

Aligned under the front of the second trailer with the kingpin locked

Answer

When coupling a second trailer, the converter dolly should be positioned so that it is correctly aligned under the front of the second trailer, with the kingpin locked in the fifth wheel. The safety chains and air/electrical lines must be properly connected before moving.

Question 3

What is 'crack the whip' and why is it more dangerous with doubles/triples?

Accepted Answer

Rear trailer amplification where each unit swings more violently during maneuvers, increasing rollover risk

Answer

'Crack the whip' refers to the rearward amplification effect where the rear trailer swings more violently than the front unit during rapid lane changes or emergency maneuvers. With doubles and triples, each additional trailer amplifies the lateral movement, making rollovers and jackknifes significantly more likely.

Question 4

Before operating doubles/triples, you should check that all trailer air connections are:

Accepted Answer

Properly coupled, not leaking, and connected to the correct lines

Answer

All glad hand (air line) connections must be properly coupled and not leaking. Glad hands must be securely locked together, with each one connected to the correct line (service or emergency). Cross-connected lines can cause brake failure — the emergency line must connect to the emergency coupler.

Question 5

When should the converter dolly's safety chains be used?

Accepted Answer

Always — they must be connected whenever the dolly is coupled to a trailer

Answer

Safety chains must ALWAYS be used when coupling a converter dolly to a trailer. If the dolly separates from the trailer (e.g., kingpin failure), the safety chains prevent the dolly from whipping around and causing catastrophic accidents. They are required for every trip, not just certain conditions.

CDL Practice Test

CDL Practice Test

CDL Doubles and Triples Practice Test