At about what speed can tires start to ride up on a wedge of water?
Manitoba Commercial overview
Manitoba Commercial: Weather, winter roads, skids and jackknifing
Ice and snow, reduced visibility, black ice, Manitoba winter and ice roads, strong winds, hydroplaning, wet brakes, the causes of skids, skid recovery and jackknifing.
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- 13 questions
- Topic drill
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Study reference: MPI Professional Driver's Manual (PDF, Dec. 2025), Ch. 2 Efficient and safe vehicle operation — Adverse weather, Winter road driving, Hydroplaning, Skids, Jackknifing
All 13 questions in this test
Every question and its answer choices. The correct answers and explanations appear when you take the test above.
At about what speed can tires start to ride up on a wedge of water?
- Only above 120 km/h
- At any speed on dry roads
- About 70 km/h and higher
- Below 20 km/h
How does MPI define a jackknife?
- The trailer tips over on its side
- The drive wheels spin on ice
- The trailer swings 15 degrees and then recovers by itself
- The tractor at 90° or less to the trailer
What is the recommended speed on Manitoba ice roads for vehicles of 7 tonnes GVWR or more?
- 70 km/h
- 50 km/h
- 15 km/h
- 30 km/h
What can happen if you brake a tractor-trailer using only the trailer brakes?
- The unit can jackknife
- The trailer will stop more smoothly
- The ABS light will come on
- The air dryer will purge
Your skid was caused by over-braking. What is the first thing to do?
- Shift into a lower gear at once
- Press the brake harder and hold it
- Release the brake so the wheels turn again
- Turn the wheel opposite to the skid
Your load needs to be unloaded at a lakeside camp on a winter road. Where may you do it?
- On the ice, if another truck is not nearby
- Anywhere the road is wide enough
- Only on land, never on the ice
- On the ice, if the truck is turned off
How far apart should trucks travelling the same way on an ice road be staggered?
- About one kilometre
- About 100 m
- About five kilometres
- About 300 m
How can a manual front brake limiting valve help on slippery roads?
- It increases front braking for shorter stops
- It locks the drive wheels for traction
- It turns off the trailer brakes
- It reduces front braking to improve steering
The rear of your bus skids to the left. Which way do you steer first?
- To the right
- To the left
- Straight ahead
- Sharply right, then brake
You are driving in strong gusting winds. Which action does MPI advise?
- Speed up to get through the gusts faster
- Pass other vehicles to get clear of them
- Drive close beside other vehicles for shelter
- Reduce speed and grip the wheel firmly
Where should you drive on a winter ice road?
- Wherever the ice looks smoothest
- Close to the centre, away from the snow banks
- Close to the snow banks for better grip
- On the right edge to leave room for others
What causes most skids?
- Using the radio while driving
- Carrying a light load
- Driving too fast for road conditions
- Tires that are slightly over-inflated
Why are bridges and overpasses especially dangerous in winter?
- Black ice can form on them from condensation
- They are salted less often than roads
- Snow plows are not allowed on them
- They are always narrower than the highway
Weather, winter roads, skids and jackknifing: key rules to remember
Our summary of what the official handbook says on this topic, in our own words. Read it before or after the practice questions above, then check the original chapter. Read the official chapter ↗
Ch. 2 Adverse weather and reduced visibility (p. 45)
- On ice or snow: start slowly and test steering and brakes, lower speed, use chains if needed, brake lightly, avoid jerky steering, keep windows and lights clean, ventilate the cab.
- A manual front brake limiting valve can reduce front braking to improve steering on slippery roads.
- In fog, heavy rain or snow use low beams; if visibility is too poor, use hazard lights and pull off the road until it improves.
Ch. 2 Winter and winter road driving (pp. 46–47)
- Bridges and overpasses can form black ice near freezing or in extreme cold.
- Smaller vehicles may follow a large vehicle through a storm; allow for them when braking.
- On ice roads, the recommended speed for vehicles of 7 tonnes GVWR or more is 15 km/h; faster can create an ice wave and break the ice.
- Do not use a winter road before it officially opens.
- Drive near the centre of ice roads, away from the snow banks at the sides.
- Never stop or park trucks on an ice road; load and unload only on land.
- Trucks travelling the same way on an ice road should be staggered one kilometre apart.
- Do not cross a pressure-ridge ramp bridge whose planks have lifted or twisted.
- First-time winter road drivers should go with an experienced driver; a 24-hour log book is still required.
Ch. 2 Wind, hydroplaning and wet brakes (p. 48)
- In strong wind: slow down, grip the wheel firmly, correct gently, avoid passing, increase following distance.
- Below about 50 km/h tires normally cut through water; at about 70 km/h and above they can ride on a wedge of water.
- Worn or under-inflated tires or deep water can cause hydroplaning even below 50 km/h.
- Drive through water with a light drag on the brakes, then apply them lightly to dry them.
Ch. 2 Skids and jackknifing (pp. 49–51)
- Most skids come from driving too fast for conditions; causes are overbraking, overaccelerating and oversteering.
- Using the trailer brakes alone on a tractor-trailer can cause a jackknife.
- Correct the cause first: release the brake for a braking skid, release the accelerator for a power skid, push in the clutch if too low a gear caused it.
- Steer in the direction the rear end is skidding, then counter-steer slightly as it straightens.
- If a trailer starts to skid while braking, release pedal pressure; avoid using the hand valve by itself.
- A jackknife is when the tractor reaches an angle of 90° or less to the trailer, usually after the drive wheels lose traction.
Study the Weather, winter roads, skids and jackknifing rules as flashcards →
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