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View All PlansIn the District of Columbia, double trailers are effectively restricted, and triple trailers are not allowed at all. Federal law allows two “pup” trailers to have a combined length of 57 feet (not counting the length of the tractor or the connecting dolly). In DC, however, the maximum length of an entire combination vehicle (such as a semi-truck or tractor-trailer) is limited to 55 feet unless an oversize permit is obtained.
For this reason, carriers may operate double pups outside DC, such as on interstate highways. However, for transport into the District, they may transfer the load to a van or smaller truck or break down (separate) the trailers and pull only one at a time into the city.
To drive combination vehicles, you must obtain a Class A CDL. First, you must pass the General Knowledge Test and a skills test to obtain any class of CDL. To obtain a Class A CDL in particular, you must also pass the Combination Vehicles knowledge test on the theory of operating combination vehicles. Under federal regulations, to drive combination vehicles with two or even three trailers or semi-trailers, you must also obtain a Double/Triple (T) endorsement on your Class A CDL. (However, triple trailers are prohibited in DC.) To obtain this endorsement, you must pass the Double/Triple knowledge test. (No skills test is required for this endorsement.)
All these knowledge tests are based on the official District of Columbia CDL manual (District of Columbia CDL Handbook). You likely studied parts of this manual to get your CDL. The Double/Triple endorsement test is based on Chapter 7: Doubles and Triples.
We have created a set of study tools to help aspiring drivers like you pass their knowledge exams on their first try. This District of Columbia Doubles and Triples Endorsement Practice Test, one of five we offer, supplements the official manual with intensive practice. It’s based on Chapter 7 of the official CDL manual, just like the official Double/Triple knowledge test. It’s up to date as of October, 2025. The 20 multiple-choice practice questions and answers on this practice test address such topics as air lines, converter dollies, coupling, following distance, rearward amplification, and rollovers.
Our AI Assistant can help you figure out the answer to any practice question. You can ask it to give you a hint or rephrase the question. You can also ask your own questions. If you still miss the question, the AI Assistant will immediately give you the correct answer and an accompanying explanation.
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