Speed Limits & Following Distance — Idaho
Idaho CDL practice test: 416 free practice questions (Based on the official driver handbook). The official format is not yet verified; check the official site before your test. Speed Limits & Following Distance: 10 questions.
Posted speed limits, school and construction zones, stopping and following distance.
This topic page is still being reviewed against the official handbook. Until review is finished it is hidden from search engines.
| Topic / Metric | Value |
|---|---|
| Topic | Speed Limits & Following Distance |
| License test | Idaho CDL permit (CLP) knowledge tests |
| Topic questions | 10 (2% of 416 total) |
| Review status | This topic page is still being reviewed against the official handbook. Until review is finished it is hidden from search engines. |
Official handbook
Not yet verified
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Questions (10)
1. If another driver is tailgating you, you should:
- Move into the left lane.
- Speed up.
- Increase the distance between you and the vehicle ahead. ✓
Answer: C. Increase the distance between you and the vehicle ahead.
When someone is tailgating you, increase the distance between your vehicle and the vehicle ahead of you. The handbook lists increasing your following distance as one of the things to do when you are being tailgated. Opening up room in front of you means you won't have to make sudden speed or direction changes, and it also gives the tailgater an easier chance to get around you. The same section warns against speeding up, since being tailgated at a low speed is safer than at a high speed, and it says to avoid tricks like flashing brake lights or turning on taillights.
2. When driving a 50-foot truck at 50 mph, your minimum following distance should be:
- Four seconds.
- Five seconds.
- Six seconds. ✓
Answer: C. Six seconds.
At 50 mph in a 50-foot truck, allow at least six seconds of following distance. The handbook's following-distance rule starts with one second for every ten feet of vehicle length, so a 50-foot truck gets a five-second base. It then says to add one second when your speed is above 40 mph. At 50 mph, that extra second brings the minimum to six seconds. The same passage shows the pattern with a 40-foot truck: four seconds normally, or five seconds over 40 mph.
3. How does doubling your speed from 20 mph to 40 mph affect your vehicle's braking distance?
- It stays about the same.
- It doubles.
- It quadruples. ✓
Answer: C. It quadruples.
Doubling your speed from 20 mph to 40 mph makes your braking distance four times longer, so it quadruples. The handbook's stopping-distance figure states that when you double speed from 20 to 40 mph, the impact is four times greater and the braking distance is also four times longer. It gives the same pattern for higher speeds, and it says slowing down can reduce braking distance. So the change from 20 to 40 mph is not a small increase or a doubling; the distance needed to stop grows to four times its earlier length.
4. If you are braking on dry pavement while traveling at 55 mph, how much distance will brake lag add to your overall stopping distance?
- 32 feet ✓
- 45 feet
- 20 feet
Answer: A. 32 feet
Brake lag adds 32 feet to your overall stopping distance. The handbook explains that with air brakes there is a delay while air flows through the lines before the brakes actually work. At 55 mph on dry pavement, that brake lag distance is about 32 feet. The handbook also lists brake lag as one of the four parts of total stopping distance, along with perception, reaction, and braking distance. So the added distance from brake lag is 32 feet.
5. If you are being tailgated, you should:
- Drive on the shoulder.
- Allow the vehicle to pass. ✓
- Drive faster.
Answer: B. Allow the vehicle to pass.
If you are being tailgated, allow the vehicle to pass. The handbook's response to a tailgater is to make the situation calmer and give the other driver room. It says to increase your following distance so you have more room ahead, which helps you avoid sudden speed or direction changes and makes it easier for the tailgater to get around you. It also says not to speed up. Allowing the vehicle to pass matches that guidance: you are not making abrupt moves or racing the tailgater; you are opening space so it can go by.
6. On a curve, the posted speed limit:
- Is safe to be driven in any vehicle.
- Can still permit a vehicle to tip over. ✓
- Is understood to be the minimum legal speed limit.
Answer: B. Can still permit a vehicle to tip over.
The posted speed limit on a curve can still permit a vehicle to tip over. The handbook says drivers must adjust their speed for curves. If you enter too fast, either the tires lose grip and you skid off the road, or they keep grip and the vehicle rolls over. It notes that tests showed a truck with a high center of gravity may roll over even when traveling at the curve's posted limit. So the posted number is not a guarantee that every vehicle can take the curve safely; slow to a safe speed before entering and do not exceed the posted limit.
7. The faster you drive:
- The shorter your stopping distance will be.
- The longer your stopping distance will be. ✓
- The easier it will be to stop your vehicle.
Answer: B. The longer your stopping distance will be.
The faster you drive, the longer your stopping distance will be. The handbook's stopping-distance figure makes the trend clear: as speed rises, braking distance rises too. It shows that doubling speed from 20 to 40 mph makes braking distance four times longer, and tripling speed to 60 mph makes it nine times longer. Higher speed also increases crash severity. Slowing down is the way to reduce braking distance, so faster driving means you need more room to stop, not less.
8. If being tailgated, you should:
- Increase your speed.
- Increase the amount of space between your vehicle and the vehicle in front of you. ✓
- Make quick movements.
Answer: B. Increase the amount of space between your vehicle and the vehicle in front of you.
You should increase the amount of space between your vehicle and the vehicle in front of you. The handbook says that when someone is tailgating you, opening up room ahead helps you avoid sudden speed or direction changes. It also gives the tailgater an easier chance to get around you. The same passage says not to speed up and to avoid quick changes, so the safe response is to create more following distance in front rather than reacting sharply or going faster.
9. What is the average driver’s reaction time?
- 1/16 of a second
- 1/8 of a second
- 3/4 of a second ✓
Answer: C. 3/4 of a second
The average driver's reaction time is 3/4 of a second, which is the low end of the range the handbook gives. The handbook's discussion of stopping distance breaks the total into perception distance, reaction distance and braking distance. For reaction distance, it states that the average driver takes 3/4 second to 1 second to react before physically hitting the brakes, and notes that at 55 mph this accounts for 61 feet of travel. Since 3/4 of a second is the figure the handbook lists first for an average driver, it is the answer here. Reaction time is separate from perception time, which the handbook puts at 1 3/4 seconds for an alert driver.
10. What is the number one cause of death and injury in a work zone?
- Drivers speeding ✓
- Slow drivers
- Animals crossing the road
Answer: A. Drivers speeding
The number one cause is drivers speeding. The work zone section of the handbook names speeding as the leading source of injuries and deaths in roadway work zones. It tells you to watch the posted limit when you approach and drive through the zone, to keep checking your speedometer so your speed does not creep up on long construction stretches, and to slow further for bad weather, poor road conditions, or a worker close to the roadway. That is why speeding is the answer.
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Last checked: 2026-10-17 · Verified from official source
Updated: · Based on the official driver handbook