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2.6.3 – Speed and Curves

Drivers must adjust their speed for curves in the road. If you take a curve too fast, two things can happen. The tires can lose traction and continue straight ahead, so you skid off the road. Or, the tires may keep their traction and the vehicle rolls over. Tests have shown that trucks with a high center of gravity can roll over at the posted speed limit for a curve.

Slow to a safe speed before you enter a curve. Braking in a curve is dangerous because it is easier to lock the wheels and cause a skid. Slow down, as needed. Never exceed the posted speed limit for the curve. Be in a gear that will let you accelerate slightly in the curve. This will help you keep control.

2.6.4 – Speed and Distance Ahead

You should always be able to stop within the distance you can see ahead. Fog, rain, or other conditions may require that you slow down to be able to stop in the distance you can see. At night, you cannot see as far with low beams as you can with high beams. When you must use low beams, slow down.

2.6.5 – Speed and Traffic Flow

When you are driving in heavy traffic, the safest speed is that of other vehicles. Vehicles going the same direction at the same speed are not likely to run into one another. In many states, speed limits are lower for trucks and buses than for cars. It can vary as much as 15 mph. Use extra caution when you change lanes or pass on these roadways. Drive at the speed of the traffic if you can without going at an illegal or unsafe speed. Keep a safe following distance.

The main reason drivers exceed the speed limit is to save time. But, anyone trying to drive faster than the speed of traffic will not be able to save much time. The risks involved are not worth it. If you go faster than the speed of other traffic, you will have to keep passing other vehicles. This increases the chance of a crash and is more tiring. Fatigue increases the chance of a crash. Going with the flow of traffic is safer and easier.

2.6.6 – Speed on Downgrades

Your vehicle's speed will increase on downgrades because of gravity. Your most important objective is to select and maintain a speed that is not too fast for the following:

  • Total weight of the vehicle and cargo.
  • Length of the grade.
  • Steepness of the grade.
  • Road conditions.
  • Weather.

If a speed limit is posted or there is a sign indicating “Maximum Safe Speed,” never exceed the speed shown. Also, look for and heed warning signs indicating the length and steepness of the grade. You must use the braking effect of the engine as the principal way of controlling your speed on downgrades.

The braking effect of the engine is greatest when it is near the governed RPMs and the transmission is in the lower gears. Save your brakes so you will be able to slow or stop as required by road and traffic conditions. Shift your transmission to a low gear before starting down the grade and use the proper braking techniques. Please read carefully the section on going down long, steep downgrades safely in “Mountain Driving.”

2.6.7 – Roadway Work Zones

Speeding traffic is the number one cause of injury and death in roadway work zones. Observe the posted speed limit at all times when approaching and driving through a work zone. Watch your speedometer and do not allow your speed to creep up as you drive through long sections of road construction. Decrease your speed for adverse weather or road conditions. Decrease your speed even further when a worker is close to the roadway.

Multiple-Choice Questions:

Question #98 (1 of 6)

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When is the braking effect of the engine at its greatest?

  • When it is well below the governed RPMs and the transmission is in the higher gears.
  • When it is well below the governed RPMs and the transmission is in the lower gears.
  • When it is well above the governed RPMs and the transmission is in the higher gears.
  • When it is near the governed RPMs and the transmission is in the lower gears.
The braking effect of the engine is greatest when it is near the governed RPMs and the transmission is in the lower gears.
The faster the engine is turning, the greater the braking effect of the engine brake, but do not exceed the governed RPMs of the engine.
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Question #95 (2 of 6)

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Which of the following is true about driving through a curve in a truck with a high center of gravity?

  • Ride the brakes slightly in the curve. This will help you keep control.
  • Be in a gear that will let you accelerate slightly in the curve. This will help you keep control.
  • Staying on the brake while slightly pressing the accelerator at the same time will balance the forces throughout the curve, making the truck more stable
  • Trucks with a high center of gravity can go around a curve a little more quickly than a truck with a lower center of gravity
Slow to a safe speed before you enter a curve. Braking in a curve is dangerous because it is easier to lock the wheels and cause a skid. Slow down as needed. Do not ever exceed the posted speed limit for the curve. Be in a gear that will let you accelerate slightly in the curve. This will help you keep control.
You will not normally be on the accelerator through the curve, but that is how you handle an emergency. This is an advanced technique, so don't worry about this just yet. Focus on getting your speed down where it needs to be before you enter the curve.
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Question #99 (3 of 6)

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What is the number one cause of injury and death in roadway work zones?

  • Rain or snow
  • Inattentive construction workers
  • Speeding traffic
  • Heavy traffic
Speeding traffic is the number one cause of injury and death in roadway work zones.
Getting a ticket for speeding in a construction zone is catastrophic for a professional driver. Enforcement is very strict. Do not try to save time speeding through construction zones.
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Question #97 (4 of 6)

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What is the safest speed to drive in heavy traffic?

  • The safest speed is the speed of the vehicles in the lane furthest to the right
  • The safest speed is slightly slower than the vehicles around you
  • The safest speed is slightly faster than the vehicles around you
  • The safest speed is that of other vehicles.
When you are driving in heavy traffic, the safest speed is that of other vehicles. Vehicles going the same direction at the same speed are not likely to run into one another.
Go with the flow! Now you know where that saying comes from. Well, at least I think so!
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Question #96 (5 of 6)

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How quickly must you be able to stop?

  • Within the distance you can see ahead.
  • Within 100 ft if you're traveling at less than 50 mph
  • In less than 1/2 of the length of your vehicle
  • Quickly enough to prevent the vehicle behind you from running into the DOT bumper on the back of your trailer
You should always be able to stop within the distance you can see ahead. Fog, rain or other conditions may require that you slow down to be able to stop in the distance you can see. At night, you cannot see as far with low beams as you can with high beams. When you must use low beams, slow down.
Adjust your speed according to road conditions and visibility. If you can not stop within the distance you can see, then you're going too fast for conditions.
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Question #94 (6 of 6)

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What have tests shown about trucks with a high center of gravity?

  • They can cause congested roadways because of their additional length
  • They can roll over at the posted speed limit for a curve.
  • They can go around a curve a little more quickly than a truck with a lower center of gravity
  • If you follow the speed limit in a curve you'll be fine because posted speed limits consider heavily loaded trucks with a high center of gravity
Tests have shown that trucks with a high center of gravity can roll over at the posted speed limit for a curve.
You must get your speed down before entering a curve. Enter a curve too fast and it might be your last. Stay well below the posted speed limit in the curve. They design those speed limits for cars, not for loaded trucks with a high center of gravity.
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