CDL Combination Vehicles — All Questions

Why do combination vehicles need a longer following distance than smaller vehicles?

• a.Because they use less fuel
• b.Because the trailer has no brakes
• c.Because trailers have brighter lights
• d.Because they are heavier and longer, so they take more time and distance to stop✓

Combination vehicles are heavy and long, so they need much more distance and time to stop than cars. A good rule is at least one second of following distance for every 10 feet of vehicle length at low speeds, adding a second above 40 mph. More space gives you time to react and stop safely.

At 50 mph in a 60-foot combination vehicle, about how many seconds of following distance should you keep?

• a.1 second
• b.At least 7 seconds (6 for length plus 1 for speed over 40 mph)✓
• c.3 seconds
• d.2 seconds

Using the rule of 1 second per 10 feet of length, a 60-foot vehicle needs 6 seconds, and you add 1 second for speeds over 40 mph, for a total of about 7 seconds. This extra space accounts for the vehicle's long stopping distance. In bad weather or on hills you should allow even more.

Why are combination vehicles more likely to roll over than they might appear?

• a.Because the brakes are too strong
• b.Trucks with a high center of gravity can roll over at highway speeds on ramps even when they feel stable to the driver✓
• c.Because the trailer is always empty
• d.Because the tires are too wide

A loaded combination vehicle can roll over on a curve or ramp at a speed that feels safe because the driver cannot feel the trailer beginning to tip. The high center of gravity and trailer lag make rollover happen suddenly. Slowing well before ramps and curves is the safe practice.

When driving a combination vehicle on a curved highway exit ramp, what should you do?

• a.Coast in neutral through the curve
• b.Brake hard in the middle of the curve
• c.Slow down before the ramp to a speed well below the posted ramp limit, because the limit may be too fast for a loaded truck✓
• d.Maintain highway speed to keep momentum

You should slow down before entering a curved ramp, often to a speed below the posted advisory limit, because those limits are set for cars, not heavy trucks. Braking in the curve can cause a skid or rollover. Reducing speed before the curve lets you drive through it under control.

How does the trailer respond to steering inputs compared to the tractor, and why does this matter?

• a.The trailer steers itself
• b.The trailer lags behind and can swing or off-track, so drivers must plan turns and lane changes with extra room✓
• c.The trailer never moves independently
• d.The trailer responds instantly to steering

The trailer follows and reacts more slowly than the tractor, lagging behind in turns and lane changes and off-tracking to the inside. This means drivers must plan turns wide and check that the trailer clears obstacles and other lanes. Abrupt steering can make the trailer swing dangerously.

What is the safest way to brake in a combination vehicle to avoid a skid?

• a.Pump the brakes rapidly at all times
• b.Slam the brakes to stop quickly
• c.Only use the trailer hand valve to stop
• d.Brake early and smoothly, keeping the vehicle straight, so the wheels keep traction✓

You should brake early, smoothly, and while the vehicle is as straight as possible so the wheels keep traction and the trailer does not swing. Sudden or hard braking, especially in a turn, can lock the wheels and cause a jackknife. Leaving extra space lets you brake gradually.

Why should you generally avoid using the trailer hand valve (trolley/spike valve) to control the vehicle in normal driving?

• a.It turns off the headlights
• b.It disconnects the air lines
• c.It raises the landing gear
• d.Applying only the trailer brakes can cause the trailer to skid and jackknife✓

Using the trailer hand valve alone applies only the trailer brakes, which can lock the trailer wheels and cause a skid or jackknife, especially on slippery roads. Normal braking should use the foot brake, which applies brakes on all wheels together. The hand valve is not a substitute for the service brakes.

When changing lanes or merging in a combination vehicle, why must you allow extra space and time?

• a.Because the vehicle is long and the trailer off-tracks, so you need more room for the whole rig to clear✓
• b.Because the engine is slow to start
• c.Because the trailer has no mirrors
• d.Because the trailer brakes are stronger

A combination vehicle is long, accelerates slowly, and the trailer off-tracks, so you need more space and time to change lanes or merge safely. You must be sure the entire rig, including the trailing trailer, will clear other vehicles. Checking mirrors and signaling early are essential.

On a slippery road, how should you adjust your driving in a combination vehicle to prevent skids?

• a.Reduce speed, increase following distance, and brake and steer gently to keep traction✓
• b.Brake harder than usual
• c.Drive at your normal speed
• d.Use only the trailer brakes

On wet, snowy, or icy roads you should slow down, leave much more following distance, and make all inputs gentle to keep the tires from losing traction. Sudden braking or steering can cause the trailer to skid or jackknife. Smooth, gradual control is the key to staying stable on slippery surfaces.

Why is it important to check your mirrors frequently when driving a combination vehicle?

• a.To check the paint
• b.To monitor the trailer position, watch for trailer skids or tire problems, and confirm the trailer is tracking properly✓
• c.To read road signs behind you
• d.To watch the sky

Frequent mirror checks let you monitor the trailer's position, spot the early signs of a trailer skid or jackknife, and catch problems like a smoking tire or shifting load. Because the trailer lags and off-tracks, mirrors are your main way to see what it is doing. Early detection gives you time to react safely.