Mississippi CDL — General Knowledge practice
Mississippi CDL — General Knowledge: Speed & Space Management practice test
Choosing a safe speed, keeping a space cushion, adjusting for weather and traffic, and understanding stopping distance.
Content reviewed against official driver handbooks · August 12, 2026
14 questions · pass with 11 correct. You get instant feedback and an explanation after every answer.
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12 sample Speed & Space Management questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.
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1. In heavy traffic, what is generally the safest speed?
Correct answer: The speed of the other vehicles, if that is legal and safe
When everyone travels the same way at the same pace, collisions are less likely. Constant passing raises crash risk and adds fatigue.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Speed and Traffic Flow)
2. What should be the main way you control speed on a downgrade?
Correct answer: The braking effect of the engine
Save the brakes for slowing or stopping when traffic requires it. Engine braking is strongest near governed rpm in the lower gears.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Speed on Downgrades)
3. What is the leading cause of injuries and deaths in highway work zones?
Correct answer: Speeding traffic
Obey posted work zone limits, don't let speed creep up through long construction areas, and slow further when workers are near the road.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Roadway Work Zones)
4. With a lot of water on the road, hydroplaning can begin at speeds as low as:
Correct answer: 30 mph
It doesn't take much water. Low tire pressure and worn tread make hydroplaning more likely.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Matching Speed to the Road Surface)
5. According to accident reports, what do trucks and buses most often run into?
Correct answer: The vehicle ahead of them
Following too closely is the most frequent cause. A smaller vehicle ahead can usually stop faster than you can.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Space Ahead)
6. How fast should you drive in relation to how far you can see?
Correct answer: Slow enough that you can always stop within the distance you can see
Fog, rain, and darkness shorten your sight distance, so slow down. At night, stay within the range of your headlights.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Speed and Distance Ahead)
7. On a wet road, by about how much should you reduce your speed?
Correct answer: About one-third, such as from 55 to about 35 mph
Wet roads can double stopping distance, so slow down by about a third. On packed snow cut speed by half or more, and on ice slow to a crawl.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Matching Speed to the Road Surface)
8. If you triple your speed from 20 mph to 60 mph, how much greater do impact and braking distance become?
Correct answer: About 9 times greater
Doubling speed makes them four times greater and tripling makes them about nine times greater. At 80 mph they reach about 16 times the 20 mph figures.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Stopping Distance)
9. At 55 mph in ideal conditions, what minimum total stopping distance does the manual give?
Correct answer: About 419 feet
Perception, reaction, and braking distance together add up to at least 419 feet at 55 mph.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Stopping Distance)
10. Why may a modern truck need a lower gear going down a hill than it needed to climb it?
Correct answer: Low-friction parts, streamlining, and stronger engines leave less to hold it back downhill
Older trucks could often use the climbing gear for descending. Newer trucks climb in higher gears and roll more freely, so they may need a lower gear to descend.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Select the Right Gear before Starting Down the Grade)
11. Why can a truck with a high center of gravity be in danger even at a curve's posted speed?
Correct answer: Tests show such trucks can roll over at the posted curve speed
Slow to a safe speed before the curve, never exceed the posted curve speed, and avoid braking in the curve.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Speed and Curves)
12. Below 40 mph, the manual's following-distance rule calls for at least how much time per 10 feet of vehicle length?
Correct answer: One second
Allow one second for each 10 feet of length, and add one more second above 40 mph. Slippery roads call for even more space.
Source: Mississippi CDL Manual — Section 2: Driving Safely (Space Ahead)
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