ASCE Transportation and Infrastructure Planning 2

Question 1

Under the Greenshields linear speed-density model, maximum flow occurs at what density?

Accepted Answer

One-half of jam density

Answer

Greenshields' parabolic flow-density curve peaks at k = kj/2.

Question 2

A freeway lane has a free-flow speed of 60 mph and a jam density of 200 veh/mi. Using Greenshields' model, what is the lane capacity?

Accepted Answer

3,000 veh/h

Answer

Capacity = vf × kj / 4 = 60 × 200 / 4 = 3,000 veh/h.

Question 3

An approach carries 1,800 veh/h, with a peak 15-minute volume of 500 vehicles. What is the peak hour factor?

Accepted Answer

0.90

Answer

PHF = 1,800 / (4 × 500) = 0.90.

Question 4

Which statement about space mean speed is correct?

Accepted Answer

It is the harmonic mean of spot speeds over a point

Answer

Space mean speed is the harmonic mean of spot speeds and is less than or equal to time mean speed.

Question 5

Under the Highway Capacity Manual, which measure defines level of service on a basic freeway segment?

Accepted Answer

Density in pc/mi/ln

Answer

The HCM uses density in passenger cars per mile per lane as the LOS measure for basic freeway segments.

ASCE - American Society of Civil Engineers Certification Practice Test