ACTAR Roadway Analysis 3 ā Questions and Answers
Question 1: A vehicle leaves four tire marks totaling 120 feet on a surface with a drag factor of 0.70. Using the basic skid speed formula, what is the minimum speed estimate?
- Approximately 51 mph (Correct answer)
- Approximately 63 mph
- Approximately 39 mph
- Approximately 72 mph
Correct answer: Approximately 51 mph
S = ā(30 Ć d Ć f) = ā(30 Ć 120 Ć 0.70) = ā2520 ā 50.2 mph, rounded to approximately 51 mph.
Question 2: Which AASHTO design element directly determines the minimum sight distance available on a crest vertical curve?
- Superelevation rate
- K-value (Correct answer)
- Lane width
- Shoulder width
Correct answer: K-value
The K-value (length per percent of A) determines how gently the crest rises and falls, directly controlling available sight distance.
Question 3: What does a negative super elevation (adverse crown) mean for a vehicle traversing a horizontal curve?
- The pavement slopes away from the curve center, adding to the centrifugal effect (Correct answer)
- The pavement slopes toward the curve center, increasing available friction
- The road is banked correctly for the design speed
- The cross-slope meets AASHTO minimum standards
Correct answer: The pavement slopes away from the curve center, adding to the centrifugal effect
Adverse crown means the pavement tilts outward (away from the curve center), requiring more friction to prevent lateral sliding than a properly superelevated curve.
Question 4: In a traffic accident reconstruction, what is a 'critical speed' scuff mark?
- A skid caused by emergency braking on a straight road
- A curved tire mark deposited when a vehicle exceeds the critical speed of a curve (Correct answer)
- A mark left by a tire blowout
- A yaw mark from ABS activation
Correct answer: A curved tire mark deposited when a vehicle exceeds the critical speed of a curve
Critical speed scuff marks are curved yaw marks that allow reconstructionists to calculate the speed at which the vehicle was traveling through a curve.
Question 5: How is the radius of a circular arc roadway curve typically measured in the field for accident reconstruction?
- By the chord-middle-ordinate method using a tape and string line (Correct answer)
- By reading the posted advisory speed sign
- By GPS triangulation alone
- By counting lane markings per curve length
Correct answer: By the chord-middle-ordinate method using a tape and string line
The chord-middle-ordinate (chord-sagitta) method uses a known chord length and the middle ordinate to calculate R = CĀ²/8M + M/2.
Question 6: Which pavement distress type most significantly reduces available friction for braking vehicles?
- Longitudinal cracking
- Polished aggregate (bleeding/flushing) (Correct answer)
- Edge cracking
- Transverse thermal cracking
Correct answer: Polished aggregate (bleeding/flushing)
Polished aggregate or bleeding (excess asphalt) surfaces dramatically reduce macro-texture and available friction, lowering the effective drag factor.
Question 7: What is the significance of the 'point of curvature' (PC) in roadway geometry?
- The midpoint of a horizontal curve
- The point where a tangent transitions into a horizontal circular curve (Correct answer)
- The highest elevation point of a vertical curve
- The end of the superelevation runoff zone
Correct answer: The point where a tangent transitions into a horizontal circular curve
The PC is the beginning of a horizontal circular curve where the straight tangent section ends and curved alignment begins.
ACTAR Roadway Analysis 3
A vehicle leaves four tire marks totaling 120 feet on a surface with a drag factor of 0.70.
Using the basic skid speed formula, what is the minimum speed estimate?