ACTAR Human Factors 4 — Questions and Answers
Question 1: What is the average total stopping distance (perception-reaction + braking) for a driver traveling at 55 mph on dry pavement with a PRT of 1.5 seconds and a deceleration rate of 0.7g?
- Approximately 240 feet (Correct answer)
- Approximately 170 feet
- Approximately 320 feet
- Approximately 120 feet
Correct answer: Approximately 240 feet
PRT distance ≈ 80.7 ft/s × 1.5 s = 121 ft; braking distance = v²/(2 × 0.7 × 32.2) ≈ 120 ft; total ≈ 241 ft.
Question 2: Older drivers (65+) generally exhibit longer perception-reaction times primarily due to which physiological change?
- Reduced muscle strength
- Slower central nervous system processing speed (Correct answer)
- Decreased peripheral vision width
- Increased startle response
Correct answer: Slower central nervous system processing speed
Age-related slowing of central neural processing is the primary cause of longer reaction times in older drivers, independent of sensory changes.
Question 3: A driver claims they 'looked but didn't see' a motorcyclist before a collision. Which human factors explanation best accounts for this?
- The driver was legally blind
- Saccadic eye movement prevented any fixation on the motorcycle
- The motorcycle was in a visual scan but not attended to (looked but not seen) (Correct answer)
- The driver deliberately avoided looking at the intersection
Correct answer: The motorcycle was in a visual scan but not attended to (looked but not seen)
'Looked but failed to see' is a recognized phenomenon where a glance occurs but attention is not allocated to the target, resulting in no conscious perception.
Question 4: Which of the following describes the 'motion camouflage' effect relevant to motorcycle crashes?
- Motorcycles are painted in camouflage colors
- A closing vehicle appears stationary when approaching head-on because its bearing angle does not change (Correct answer)
- Motorcycles move too fast for drivers to track them
- Motion camouflage is a lighting artifact unique to nighttime
Correct answer: A closing vehicle appears stationary when approaching head-on because its bearing angle does not change
When an object approaches on a constant bearing (direct interception path), it appears stationary against the background—making an oncoming motorcycle difficult to detect.
Question 5: What does research on cell phone distraction indicate about hands-free vs. hand-held phone conversations while driving?
- Hands-free conversations are significantly safer than hand-held
- Both produce comparable cognitive distraction and crash risk elevation (Correct answer)
- Hand-held phones are legal because they are safer than texting
- Cognitive distraction disappears within 2 seconds of ending a call
Correct answer: Both produce comparable cognitive distraction and crash risk elevation
Research, including NHTSA studies, shows that hands-free and hand-held phone conversations produce similar cognitive distraction and comparable crash risk increases.
Question 6: In a rear-end collision analysis, which factor most directly determines whether a following driver had adequate time to perceive and react to a lead vehicle braking?
- The color of the lead vehicle's brake lights
- Time-to-collision (TTC) at the moment brake lights activated (Correct answer)
- The posted speed limit on the roadway
- The following driver's age
Correct answer: Time-to-collision (TTC) at the moment brake lights activated
TTC at brake light activation determines whether the following driver had sufficient margin (typically ≥ PRT + braking time) to avoid collision.
Question 7: Which criterion is used to determine whether a pre-impact event was within a driver's 'avoidance window'?
- Whether the driver applied brakes before impact
- Whether the hazard was within the driver's lane at time of detection
- Whether sufficient time and distance existed for the driver to perceive, react, and complete an avoidance maneuver (Correct answer)
- Whether the event occurred in daylight
Correct answer: Whether sufficient time and distance existed for the driver to perceive, react, and complete an avoidance maneuver
The avoidance window requires that time-distance analysis confirm perception was possible and that reaction plus maneuver could have been completed before impact.
ACTAR Human Factors 4
What is the average total stopping distance (perception-reaction + braking) for a driver traveling at 55 mph on dry pavement with a PRT of 1.5 seconds and a deceleration rate of 0.7g?