Following distance, trucks and motorcycles

Key points

1. Use the three second rule to check your following distance; it works at any speed.

   Source: Handbook p. 127

   “It is called the “threesecond rule,” and it works at any speed.”
   Delaware Driver Manual, Handbook p. 127

2. Some situations, such as slippery roads, call for a four second following distance.

   Source: Handbook p. 128

   “In the following situations, you may need a four-second following distance to be safe. • On slippery roads - Because you need more distance to stop your vehicle on slippery roads, you must leave more space in front of you.”
   Delaware Driver Manual, Handbook p. 128

3. You need a gap of about four seconds to merge with other traffic.

   Source: Handbook p. 130

   “Anytime you want to merge with other traffic, you need a gap of about four seconds.”
   Delaware Driver Manual, Handbook p. 130

4. If you are tailgated and there is a right lane, move over to the right.

   Source: Handbook p. 129

   “If you are being followed too closely and there is a right lane, move over to the right.”
   Delaware Driver Manual, Handbook p. 129

5. Allow at least four seconds between your vehicle and a truck.

   Source: Handbook p. 103

   “Allow at least four seconds between your vehicle and the truck”
   Delaware Driver Manual, Handbook p. 103

6. After passing a truck, move back only when you can see its front in your rearview mirror.

   Source: Handbook p. 103

   “Be sure to move back only when you can see the front of the truck in your rearview mirror.”
   Delaware Driver Manual, Handbook p. 103

7. Two thirds of commercial vehicle crashes happen while backing; never cross behind a backing truck.

   Source: Handbook p. 104

   “Sixty-six percent of all commercial vehicle crashes are while backing; therefore, never try to cross behind a truck which is preparing to back up.”
   Delaware Driver Manual, Handbook p. 104

8. Follow a motorcycle by 2 seconds under 40 mph and 4 seconds above 40 mph.

   Source: Handbook p. 100

   “Following distance behind the motorcyclist should be at a two second count when traveling at speeds under 40 mph and a four second count for speeds above 40 mph.”
   Delaware Driver Manual, Handbook p. 100

9. Windy conditions can move a motorcycle out of its lane.

   Source: Handbook p. 100

   “Windy conditions can actually move a motorcycle out of its lane of travel.”
   Delaware Driver Manual, Handbook p. 100

10. Never share a lane with a motorcycle, even if the rider is far to one side.

    Source: Handbook p. 100

    “Never move into the same lane alongside a motorcycle even if the lane is wide and the cyclist is riding far to one side.”
    Delaware Driver Manual, Handbook p. 100

Numbers to know

3 questions from the Delaware practice test

1. 1. What following-distance method does the Delaware manual recommend for ordinary driving?

   1. Following until the lead vehicle's brake lights appear
   2. The one-car-length rule at every speed
   3. The three-second rule
   4. Keeping exactly one second behind on dry roads
   Show answer

   The three-second rule. The manual calls the three-second rule an easy way to tell whether a driver is following too closely, and says it works at any speed. A fixed car length changes meaning as speed changes, while waiting for brake lights leaves little reaction time. One second is less than the stated ordinary cushion. Choose a stationary point after the vehicle ahead passes it, count three seconds, and increase the gap when weather, visibility, load, or traffic requires more room.

2. 2. What following gap should a driver allow behind a truck to reduce the truck's rear blind-spot risk?

   1. One car length at every speed
   2. Exactly one second
   3. At least four seconds
   4. Four feet regardless of speed
   Show answer

   At least four seconds. The manual advises allowing at least four seconds behind a truck. Large vehicles have deep rear blind spots, so the truck driver may not see a car following close behind, and the trailing driver loses a clear view of traffic ahead. One car length changes meaning with speed and is not a dependable time gap. A four-foot spacing is a distance, not the recommended interval. Pick a fixed object, note when the truck reaches it, and make sure at least four seconds pass before your vehicle reaches the same point.

3. 3. Why should a Delaware driver watch for sudden motorcycle movement near bridges and large trucks?

   1. Bridges remove the need for following distance
   2. Motorcycles always stop in the center of bridges
   3. Large trucks pull motorcycles toward them
   4. Crosswinds can move a motorcycle out of its lane
   Show answer

   Crosswinds can move a motorcycle out of its lane. Crosswinds can push a motorcycle out of its lane, especially on open stretches, bridges, and near the wind blast from a fast-moving large truck. The rider may need to change speed or direction quickly, so a driver should stay alert and avoid squeezing the motorcycle's space. Trucks do not pull motorcycles toward them, and bridge location does not justify reducing the gap. Watch the rider's lane position, keep a generous buffer, and be prepared to adjust smoothly rather than making a sudden pass.

Source: the Delaware Driver Manual, Section Five: Driving Skills and Safety Tips. This lesson is a plain English summary, not the law itself; where it differs, the manual and the statute govern. Last checked 2026-09-27.