ACTAR Roadway Analysis 2

Question 1

What term describes the algebraic difference in grade between two intersecting roadway tangents in a vertical curve?

Accepted Answer

A-value

Answer

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?

Accepted Answer

The total visible stain length including shadow skids

Answer

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?

Accepted Answer

6

Answer

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?

Accepted Answer

Dry concrete

Answer

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?

Accepted Answer

The standard two-sided transverse slope directing water to both edges

Answer

Normal crown is the standard pavement cross-section with slopes from the centerline toward both edges to facilitate drainage on tangent sections.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test