This document provides guidance on safely operating combination vehicles and their components. It discusses risks associated with rollovers and off-tracking when turning, and the need for gentler steering, increased following distances, and looking ahead. It also covers proper braking techniques, railroad crossing safety, backing procedures, inspecting and using air brakes and anti-lock braking systems, coupling and uncoupling trailers, and performing brake checks.

1. Commercial Driver License
Study Group
2012

2. Combination Vehicles

3. Driving safely
• Rollover risks
– Keep cargo low and centered
– Drive slowly around curves
• Steer gently
– Rearward amplification = crack the whip effect
– Steer gently & smoothly
– Following distance is longer
– Look ahead
– Slow down at night

4. Driving safely
• Brake early
– Take longer to stop when empty than fully loaded
– Bobtail tractors
• Railroad-highway crossings
– Low slung units
– Long trailer….
– Get out of vehicle and away from tracks
– Call 911

5. Driving safely
• Skids are more likely when trailer is empty or
lightly loaded
– Use mirror to check trailer
– Release brakes to get traction back
• Turn wide
– Offtracking or cheating
– Rear wheels of last unit will offtrack the most
– Keep rear wheels near curb

6. Driving safely
• Backing a trailer
– Turn steer wheel in the opposite direction of where
you want to go
– Once the trailer starts to turn, you must turn the
wheel the other way to follow the trailer
– Position vehicle to back in a straight line
– If curved, back to the driver’s side so you can see

7. Driving safely
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Get out and look at path
Check outside mirrors
Back slowly
Correct drift by turning steering wheel in
direction of drift
• Pull up to reposition vehicle as needed

8. Combination air brakes
• Trailer hand valve - only to test trailer brakes
• Tractor protection valve
• Trailer air supply control

9. Combination air brakes
• Service air line
– Air controlled by foot brake pedal
• Emergency air line
– Air to trailer air tanks
– Loss of air pressure causes trailer emergency
brakes to come on and tractor protection valve to
close

10. Combination air brakes
• Hose couplers (Glad Hands)
– Connect service and emergency air lines from
truck or tractor to the trailer
– Color coded red, blue
– Test brakes before driving
– Keep clean – dummy couplers

11. Combination air brakes
• Trailer air tanks
– Drain each tank every day
• Shut-off valves
– Between or at end of trailers
• Trailer service, parking & emergency brakes
– After 1975 = spring brakes
– Earlier = air brakes + chocks

12. Anti-lock brakes
• After 1998 – ABS required
• Yellow ABS malfunction lamps
• Early models – hard to tell

13. Braking with ABS
• Does not change normal braking
• Activates when wheels are about to lock up
• Helps keep vehicle under control by reducing
braking pressure to a safe level
• Use only force necessary
• Brake same way
• As slow down, monitor, back off brakes

14. Coupling & Uncoupling
• Coupling – 16 steps
• Uncoupling – 10 steps

15. Inspecting a combination
• New items to inspect
– Fifth wheel (lower)
– Fifth wheel (upper)
– Air and electric lines to trailer
– Sliding fifth wheel
– Landing gear

16. Combination brake check
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Air flows to all trailers
Test Tractor Protection Valve
Test Trailer Emergency Brakes
Test Trailer Service Brakes