Civil Engineering PE Transportation and Traffic Engineering Questions and Answers

Question 1

According to the fundamental relationship of traffic flow, what is the traffic flow rate when the traffic density reaches its maximum possible value (jam density)?

Accepted Answer

Zero

Answer

The fundamental equation of traffic flow is Flow = Speed × Density. At jam density, vehicles are stopped or nearly stopped (bumper-to-bumper), so their speed is zero. Therefore, the flow rate, being the product of speed and density, is also zero.

Question 2

A horizontal curve on a two-lane rural highway has a radius of 1,200 ft and a design speed of 55 mph. According to AASHTO guidelines, which of the following is the primary purpose of applying superelevation to this curve?

Accepted Answer

To counteract the centrifugal force experienced by a vehicle.

Answer

Superelevation, or banking a curve, tilts the roadway to help vehicles navigate the turn. A component of the vehicle's weight is directed toward the center of the curve, which counteracts the outward centrifugal force. This reduces the reliance on side friction between the tires and the pavement, improving vehicle stability, safety, and driver comfort.

Question 3

An engineer is calculating the required yellow interval for a signalized intersection approach. The design speed is 40 mph, the driver perception-reaction time is 1.0 second, and the comfortable deceleration rate is 10 ft/s². The approach is on a +2% (uphill) grade. Using the standard kinematic equation, what is the minimum required yellow interval?

Accepted Answer

3.8 s

Answer

The formula for the yellow interval (Y) is: Y = t + V / (2a + 2Gg), where t = perception-reaction time, V = approach speed, a = deceleration rate, G = grade, and g = acceleration due to gravity (32.2 ft/s²). First, convert speed: V = 40 mph * 1.467 (ft/s)/mph ≈ 58.7 ft/s. Then, plug in the values: Y = 1.0 s + 58.7 ft/s / (2 * 10 ft/s² + 2 * 0.02 * 32.2 ft/s²). Y = 1.0 + 58.7 / (20 + 1.288) = 1.0 + 58.7 / 21.288 = 1.0 + 2.76 s ≈ 3.76 s. The closest answer is 3.8 s.

Question 4

According to the Highway Capacity Manual (HCM), which performance measure is primarily used to determine the Level of Service (LOS) for a basic freeway segment?

Accepted Answer

Density (passenger cars per mile per lane)

Answer

For basic freeway segments, Level of Service is defined by density, measured in passenger cars per mile per lane (pc/mi/ln). Density is a measure of vehicle proximity and is a better indicator of operational quality on uninterrupted flow facilities (like freeways) than speed, as speed can remain relatively high even as conditions worsen from LOS C to D.

Question 5

A traffic engineer needs to determine the required stopping sight distance (SSD) for a vehicle traveling at 60 mph on a roadway with a -3% downgrade. Assuming a standard perception-reaction time of 2.5 seconds and a coefficient of friction (f) of 0.30, what is the approximate SSD?

Accepted Answer

615 ft

Answer

The AASHTO formula for Stopping Sight Distance is SSD = (Perception-Reaction Distance) + (Braking Distance).  Perception-Reaction Distance = 1.47 * V * t = 1.47 * 60 * 2.5 = 220.5 ft. Braking Distance = V² / (30 * (f + G)) = 60² / (30 * (0.30 - 0.03)) = 3600 / (30 * 0.27) = 3600 / 8.1 ≈ 395.6 ft. SSD = 220.5 ft + 395.6 ft = 616.1 ft. The closest answer is 615 ft.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Transportation and Traffic Engineering Questions and Answers