ACTAR Roadway Analysis 3

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?

Accepted Answer

Approximately 51 mph

Answer

S = √(30 × d × f) = √(30 × 120 × 0.70) = √2520 ≈ 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?

Accepted Answer

K-value

Answer

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?

Accepted Answer

The pavement slopes away from the curve center, adding to the centrifugal effect

Answer

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?

Accepted Answer

A curved tire mark deposited when a vehicle exceeds the critical speed of a curve

Answer

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?

Accepted Answer

By the chord-middle-ordinate method using a tape and string line

Answer

The chord-middle-ordinate (chord-sagitta) method uses a known chord length and the middle ordinate to calculate R = C²/8M + M/2.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Roadway Analysis 3