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Difficulty: HardSpace Ahead and Following Distance

You are operating a 60-foot tractor-trailer combination on a highway route. While traveling at 35 mph through a designated work zone, you maintain the minimum following distance prescribed by CDL safety standards. After exiting the work zone onto an open interstate, you increase your cruising speed to 55 mph. According to official CDL space management guidelines, what minimum following distances must you maintain in the work zone and on the open interstate, respectively?

  1. A
    6 seconds in the work zone and 6 seconds on the open interstate
  2. 6 seconds in the work zone and 7 seconds on the open interstateAnswer
  3. C
    5 seconds in the work zone and 6 seconds on the open interstate
  4. D
    3 seconds in the work zone and 4 seconds on the open interstate

Answer

6 seconds in the work zone and 7 seconds on the open interstate
Under CDL rules, safe following distance is calculated as 1 second per 10 feet of vehicle length when traveling below 40 mph, with 1 extra second added for speeds at or above 40 mph. For a 60-foot vehicle, 35 mph requires 6 seconds (60÷1060 \div 10), and 55 mph requires 7 seconds (6+16 + 1).

Step-by-Step Solution

1
Determine the baseline following distance for the 60-foot vehicle at speeds below 40 mph.
60 ft÷10 ft/sec=6 seconds60\text{ ft} \div 10\text{ ft/sec} = 6\text{ seconds}
CDL regulations require at least 1 second for each 10 feet of vehicle length when driving under 40 mph.
2
Apply the speed adjustment factor for highway travel at 55 mph.
6 seconds+1 second=7 seconds6\text{ seconds} + 1\text{ second} = 7\text{ seconds}
At speeds of 40 mph or higher, 1 additional second must be added to compensate for increased stopping distance and brake lag.
3
Combine the calculated values for both operating conditions.
6 seconds at 35 mph and 7 seconds at 55 mph.
Provides the complete required space cushion profile for the vehicle across both speed zones.

Key Concept

CDL Space Ahead Formula: 1 second per 10 feet of vehicle length under 40 mph, plus 1 additional second at speeds of 40 mph or greater.
Estimated Time:2m 0s
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Topics

Space Ahead and Following Distance

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