ACTAR Roadway Analysis 2 — Questions and Answers
Question 1: What term describes the algebraic difference in grade between two intersecting roadway tangents in a vertical curve?
- Superelevation rate
- A-value (Correct answer)
- Cross-slope differential
- Grade break index
Correct answer: A-value
The A-value is the algebraic difference in grades (in percent) at the endpoints of a vertical curve and governs curve length design.
Question 2: When measuring skid marks to calculate pre-impact speed, which segment length is most critical for an accurate minimum-speed estimate?
- The total visible stain length including shadow skids (Correct answer)
- Only the dark scuff portion excluding shadow skids
- The gap between front and rear axle marks
- The length from impending skid to rest
Correct answer: The total visible stain length including shadow skids
Including shadow skids and any visible tire marks gives the longest defensible distance, yielding the most accurate minimum pre-impact speed.
Question 3: A roadway has a 4% upgrade followed immediately by a 2% downgrade. What is the A-value at this crest?
- 2
- 4
- 6 (Correct answer)
- 8
Correct answer: 6
A = |G1 − G2| = |4 − (−2)| = 6%; the algebraic difference accounts for sign change at a crest.
Question 4: Which roadway surface condition produces the highest coefficient of friction for a standard passenger tire?
- Dry concrete (Correct answer)
- Wet asphalt
- Packed snow
- Wet concrete
Correct answer: Dry concrete
Dry concrete typically yields the highest friction coefficients, often 0.70–0.80 for standard passenger tires.
Question 5: In the context of roadway cross-section, what does 'normal crown' refer to?
- A raised median separating opposing lanes
- The standard two-sided transverse slope directing water to both edges (Correct answer)
- The maximum superelevation on a horizontal curve
- A crowned surface used only on rural roads
Correct answer: The standard two-sided transverse slope directing water to both edges
Normal crown is the standard pavement cross-section with slopes from the centerline toward both edges to facilitate drainage on tangent sections.
Question 6: Which type of pavement marking is used to delineate the right edge of a roadway?
- Yellow solid line
- White solid line (Correct answer)
- Yellow broken line
- White broken line
Correct answer: White solid line
White solid edge lines mark the right edge of the traveled way per MUTCD guidelines.
Question 7: What is the primary purpose of a transition (spiral) curve between a tangent and a circular curve?
- To increase the posted speed limit gradually
- To allow gradual introduction of centripetal acceleration and superelevation runoff (Correct answer)
- To widen the lane for truck traffic
- To mark the beginning of a no-passing zone
Correct answer: To allow gradual introduction of centripetal acceleration and superelevation runoff
Spiral transitions allow drivers to gradually steer into the curve while superelevation and widening are introduced, improving safety and comfort.
ACTAR Roadway Analysis 2
What term describes the algebraic difference in grade between two intersecting roadway tangents in a vertical curve?