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16-Civ-B10 Traffic Engineering: May 2014

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

  1. Question 1 Intersection flows, saturation flow, clearance intervals and flow ratio
  2. Question 2 Cycle length, green splits, pedestrian check, capacity and delay
  3. Question 3 Overload probability, delay components, person delay and queue length
  4. Question 4 Multi-channel drive-in facility and Poisson arrivals at a toll plaza
  5. Question 5 Single-channel drive-up window with one and two servers
  6. Question 6 Peak-hour factor, controller types and a coordinated timing plan

Start with Question 1 →

Paper format. National Examinations, May 2014 — 98-Civ-B10 Traffic Engineering. Three-hour, open-book examination; any non-communicating calculator is permitted. Six questions are printed and five complete solutions are required, all questions being of equal value (20 marks each). The printed grading scheme is Q1 (a) to (d) 5 marks each; Q2 (a) to (e) 4 marks each; Q3 (a) to (e) 4 marks each; Q4 (a) and (b) 10 marks each; Q5 (a) to (e) 4 marks each; Q6 (10 + 5 + 5) marks. The paper states that if doubt exists as to the interpretation of a question the candidate should submit with the answer paper a clear statement of any assumptions made, and that any data required but not given can be assumed. All six questions are worked below.

Reference texts. Garber, N. J. and Hoel, L. A., Traffic and Highway Engineering, 5th ed. — Ch. 4 (traffic engineering studies: volume studies, peak-hour factor), Ch. 6 (fundamental principles of traffic flow: Poisson arrivals, deterministic and stochastic queueing, M/M/1 and M/M/N channels), Ch. 8 (intersection control: cycle length, phasing, change and clearance intervals, progression and time–space diagrams) and Ch. 10 (capacity and level of service at signalised intersections). This is the principal reference for the subject. Webster, F. V. and Cobbe, B. M., Traffic Signals, Road Research Laboratory Technical Paper No. 56 — the optimum-cycle and three-term delay formulae used throughout Questions 1 to 3. Transportation Research Board, Highway Capacity Manual — saturation-flow adjustment factors and the pedestrian-green requirement. Transportation Association of Canada, Manual of Uniform Traffic Control Devices for Canada (MUTCDC) and Geometric Design Guide for Canadian Roads — Canadian signal-timing, clearance-interval and crosswalk practice. Institute of Transportation Engineers, Traffic Engineering Handbook — controller types and coordinated timing plans.

Check: the four values assumed under the paper's own NOTE 2 (“any data required, but not given, can be assumed”). They are declared here once and used consistently in every question.

  • Bus passenger-car equivalent $E_B = 2.0$ pcu (HCM value for buses on level terrain). The paper gives bus occupancies but no pcu equivalent; note that the pcu-based and vehicle-based flow ratios in Question 1 agree exactly for any choice of $E_B$, so this assumption does not affect Questions 2 or 3.
  • Pedestrian walking speed $S_p = 1.2$ m/s (HCM 2000 / MUTCDC design value; the more recent 1.1 m/s would lengthen the pedestrian interval by about 1 s).
  • Lost time convention: the whole intergreen (amber + all-red) is taken as lost, so effective green equals displayed green. This is the conservative reading and needs no assumed start-up lost time. Webster's alternative, $L = n\ell + R$ with $\ell \approx 2$ s, would give $L = 10$ s instead of 12 s and lengthen each green by about 1 s.
  • Delay model: Webster's three-term formula, with the first two terms reported separately in Question 3(b) as the uniform and overflow components.