§ 383.91 sorts commercial motor vehicles into three groups, and the group you are tested on is the group you may drive. Group A, the combination group, is any combination of vehicles with a gross combination weight rating of 26,001 pounds or more, provided the vehicle or vehicles being towed exceed 10,000 pounds. Group B, heavy straight vehicles, is any single vehicle at 26,001 pounds or more gross vehicle weight rating, or such a vehicle towing a unit not over 10,000 pounds. Group C, small vehicles, is anything meeting neither definition that is either designed to transport 16 or more passengers including the driver, or used to transport hazardous materials in a quantity requiring placards. The towed-unit weight is what separates A from B, and it is the distinction most often got wrong: a heavy truck pulling a light trailer is still Group B.

What Chapter 1 did not say is that the groups form a ladder. Under § 383.91(c), a driver who has passed the knowledge and skills tests for Group A may operate a Group B or Group C vehicle, and a driver who has passed for Group B may operate any Group C vehicle — in each case provided they hold the endorsements those vehicles require. The ladder runs downward only. A Group B holder who wants to pull a heavy trailer does not extend their license by experience or by asking; § 383.91(c) requires them to retake and pass all related tests for the group they want. Testing up is the only way up.

One practical note about the test itself. § 383.91(b) defines a representative vehicle for the driving test as any commercial motor vehicle meeting the definition of that group. That is why a driver tested in one Group A combination is licensed for Group A combinations generally, rather than for the particular truck they hired for the day — and why choosing a test vehicle at the bottom of a group’s range has consequences for what you are then expected to handle. What each group additionally demands by way of endorsements is Chapter 4.