CDL COMBINATION VEHICLE PRACTICE
TEST EXAMINATION TEST 2026 QUESTIONS
WITH SOLUTIONS GRADED A+
⩥ Stopping distances. Answer: 'Bobtail' tractors can take longer to stop
than a combination vehicle loaded to the maximum gross weight.
⩥ Air lines color coding. Answer: The emergency line is red; the service
line is blue.
⩥ Braking distance. Answer: When a combination vehicle is empty or
lightly loaded, its braking distance increases due to poor traction.
⩥ Bobtail tractor. Answer: A tractor without semitrailers that can take
longer to stop than a fully loaded tractor-trailer.
⩥ Trailer air supply valve. Answer: You supply air to the trailer tanks by
pushing in the trailer air supply valve.
⩥ Safe distance for driving. Answer: Under good driving conditions, you
should leave at least one second of space between your vehicle and the
vehicle ahead for every 10 feet of your vehicle's length.
,⩥ Spring brakes. Answer: Semi-trailers made before 1975 that are
equipped with air brakes often do not have spring brakes.
⩥ Trailer air supply control. Answer: On newer vehicles, it is an eight-
sided red knob on the dashboard of the tractor.
⩥ Trailer rollover risk. Answer: The rear trailer is twice as likely to turn
over as the tractor.
⩥ Service air line. Answer: Also known as the control line or signal line.
⩥ Crack-the-whip effect. Answer: Due to rearward amplification, the
last trailer on a combination vehicle has the highest probability of rolling
over.
⩥ Coupling the trailer. Answer: After you have coupled the trailer, you
should start to raise the landing gear by using the appropriate
mechanism.
⩥ Air line connections. Answer: If the brakes did not release when you
pushed the trailer air supply valve, you should check the air line
connections.
⩥ Coupling a tractor to a semi-trailer. Answer: You have connected the
air lines.
, ⩥ Wheel chocks. Answer: Always use wheel chocks when parking
vehicles that rely on air pressure for emergency brakes.
⩥ Driving distance at high speed. Answer: Give yourself at least 1
second for every 10 feet of your truck's length, and another second if
you're travelling faster than 40 mph.
⩥ Emergency brakes. Answer: Trailers and converter dollies built before
1975 rely on emergency brakes that hold using air pressure.
⩥ Air flow to service line. Answer: If you cross the emergency and
service air lines, air will flow to the service line instead of the trailer air
tanks.
⩥ Pushing the knob. Answer: When you push the knob in, air will flow
through the trailer's emergency air lines to charge the trailer air brake
system.
⩥ Glad hand seals. Answer: Check the glad hand seals to ensure proper
connection of air lines.
⩥ Landing gear. Answer: Start to raise the landing gear by using the low
gear range (if the landing gear is so equipped).
TEST EXAMINATION TEST 2026 QUESTIONS
WITH SOLUTIONS GRADED A+
⩥ Stopping distances. Answer: 'Bobtail' tractors can take longer to stop
than a combination vehicle loaded to the maximum gross weight.
⩥ Air lines color coding. Answer: The emergency line is red; the service
line is blue.
⩥ Braking distance. Answer: When a combination vehicle is empty or
lightly loaded, its braking distance increases due to poor traction.
⩥ Bobtail tractor. Answer: A tractor without semitrailers that can take
longer to stop than a fully loaded tractor-trailer.
⩥ Trailer air supply valve. Answer: You supply air to the trailer tanks by
pushing in the trailer air supply valve.
⩥ Safe distance for driving. Answer: Under good driving conditions, you
should leave at least one second of space between your vehicle and the
vehicle ahead for every 10 feet of your vehicle's length.
,⩥ Spring brakes. Answer: Semi-trailers made before 1975 that are
equipped with air brakes often do not have spring brakes.
⩥ Trailer air supply control. Answer: On newer vehicles, it is an eight-
sided red knob on the dashboard of the tractor.
⩥ Trailer rollover risk. Answer: The rear trailer is twice as likely to turn
over as the tractor.
⩥ Service air line. Answer: Also known as the control line or signal line.
⩥ Crack-the-whip effect. Answer: Due to rearward amplification, the
last trailer on a combination vehicle has the highest probability of rolling
over.
⩥ Coupling the trailer. Answer: After you have coupled the trailer, you
should start to raise the landing gear by using the appropriate
mechanism.
⩥ Air line connections. Answer: If the brakes did not release when you
pushed the trailer air supply valve, you should check the air line
connections.
⩥ Coupling a tractor to a semi-trailer. Answer: You have connected the
air lines.
, ⩥ Wheel chocks. Answer: Always use wheel chocks when parking
vehicles that rely on air pressure for emergency brakes.
⩥ Driving distance at high speed. Answer: Give yourself at least 1
second for every 10 feet of your truck's length, and another second if
you're travelling faster than 40 mph.
⩥ Emergency brakes. Answer: Trailers and converter dollies built before
1975 rely on emergency brakes that hold using air pressure.
⩥ Air flow to service line. Answer: If you cross the emergency and
service air lines, air will flow to the service line instead of the trailer air
tanks.
⩥ Pushing the knob. Answer: When you push the knob in, air will flow
through the trailer's emergency air lines to charge the trailer air brake
system.
⩥ Glad hand seals. Answer: Check the glad hand seals to ensure proper
connection of air lines.
⩥ Landing gear. Answer: Start to raise the landing gear by using the low
gear range (if the landing gear is so equipped).
