Original question written by FE Exam AI Prep from the public FE Civil exam specification. Before release, a solver model re-derived the answer twice from the question alone, without its answer key, and a critic model checked the result, and the arithmetic was re-run as an executable calculation. No licensed engineer reviews these questions. It is not an NCEES question and does not come from any NCEES practice exam. FE Exam AI Prep is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCEES.
Traffic Flow, Speed and Density: FE Civil practice problem 3
For the West Basin retaining wall replacement, a project engineer preparing an agency resubmittal package uses the traffic stream relation with speed 45 mph and density 39 veh/mi. What flow rate is indicated?
- A1156 veh/hr
- B1755 veh/hr
- C1923 veh/hr
- D2103 veh/hr
Show the answer and worked solution
Answer: B — 1755 veh/hr
Worked solution
- Step 1. Use traffic flow relation
q = k v
q = 39(45) = 1755 veh/hr
Why the other choices are wrong
- Choice A
- A value of 2545 veh/hr sits about 45 percent over the direct product of density and speed, and it does not trace back to one clean arithmetic or unit-conversion mistake starting from k = 39 veh/mi and v = 45 mph; apply q = k * v once, with no scaling factor, to obtain the correct 1755 veh/hr.
- Choice C
- A computed value of 2071 veh/hr is about 18 percent higher than the direct product of the stated density and speed, and it cannot be pinned to any single identifiable error worked from k = 39 veh/mi and v = 45 mph; the flow relation q = k * v, used once with no adjustment, yields the correct 1755 veh/hr.
- Choice D
- An answer of 1369 veh/hr comes in about 22 percent short of the direct product of density and speed, and it does not follow from any single identifiable error worked from k = 39 veh/mi and v = 45 mph; the flow relation q = k * v, applied once with no discount, produces the correct 1755 veh/hr.