ACTAR Roadway Analysis 4 — Questions and Answers
Question 1: In roadway lighting analysis for a nighttime accident, which photometric quantity describes the luminous intensity per unit area of a surface as seen by an observer?
- Illuminance (lux/fc)
- Luminance (cd/m²) (Correct answer)
- Luminous flux (lumens)
- Beam candlepower
Correct answer: Luminance (cd/m²)
Luminance (cd/m²) measures the brightness of a surface as perceived by an observer, which is the relevant metric for visibility at night.
Question 2: A roadway has a posted speed of 55 mph. Using AASHTO stopping sight distance tables, what minimum sight distance is generally required on a level grade?
- Approximately 200 feet
- Approximately 360 feet
- Approximately 495 feet (Correct answer)
- Approximately 625 feet
Correct answer: Approximately 495 feet
AASHTO 2018 Green Book specifies approximately 495 feet stopping sight distance for 55 mph design speed on a level grade.
Question 3: Which of the following best describes a 'gore area' in roadway design?
- The raised median between opposing lanes
- The triangular area between a through lane and a diverging exit ramp (Correct answer)
- The paved shoulder beyond the travel lane edge
- The painted island at a signalized intersection
Correct answer: The triangular area between a through lane and a diverging exit ramp
The gore area is the triangular-shaped paved or unpaved area between the through roadway and a diverging ramp at an interchange.
Question 4: When analyzing a roadway cross-section, what is the typical maximum allowable superelevation for a rural highway in the US?
- 2%
- 4%
- 8% (Correct answer)
- 12%
Correct answer: 8%
AASHTO recommends a maximum superelevation of 8% for most rural highways, though 10% or 12% may be used in specific warmer climates without ice/snow.
Question 5: What does the 'tangent runout' portion of a superelevation transition accomplish?
- It rotates the pavement from full superelevation back to normal crown
- It rotates the outside lane from normal crown to a flat (zero) cross-slope (Correct answer)
- It introduces full superelevation immediately at the PC
- It transitions the roadway width from narrow to wide
Correct answer: It rotates the outside lane from normal crown to a flat (zero) cross-slope
Tangent runout rotates the adverse (outside) lane from its normal crown slope to a flat cross-slope, the first step before superelevation runoff begins.
Question 6: In a crash scene survey, a reconstructionist measures an 18-foot chord with a middle ordinate of 0.45 feet for a yaw mark. What is the approximate radius?
- Approximately 90 feet (Correct answer)
- Approximately 180 feet
- Approximately 360 feet
- Approximately 540 feet
Correct answer: Approximately 90 feet
R = C²/(8M) = (18²)/(8 × 0.45) = 324/3.6 = 90 feet (ignoring the small M/2 term for approximation).
Question 7: Which roadway feature is most commonly associated with run-off-road crashes on horizontal curves?
- Insufficient sight distance
- Inadequate or adverse superelevation (Correct answer)
- Excessive lane width
- Missing centerline markings
Correct answer: Inadequate or adverse superelevation
Inadequate or adverse superelevation increases the lateral friction demand, often causing vehicles to slide off the road on curves.
ACTAR Roadway Analysis 4
In roadway lighting analysis for a nighttime accident, which photometric quantity describes the luminous intensity per unit area of a surface as seen by an observer?