Urban Infrastructure and Transportation Planning
The exam tests the four-step travel demand model, capacity concepts, and the sizing logic of water, wastewater and waste systems. Expect a small arithmetic check on capacity or demand.
Principles
- Four-step model - trip generation, trip distribution (gravity model), mode choice (logit), assignment (user equilibrium); then feedback to land use.
- Capacity and level of service - v/c ratio, lane capacity around 1,800 passenger cars per hour, peak-hour factor; the unit of analysis should be the person, not the vehicle.
- Demand management - pricing, parking control, BRT, transit-oriented development, complete streets; induced demand means new capacity is partly self-cancelling.
- Utilities - per-capita water demand with peak-day and peak-hour factors, gravity sewer design, stormwater return periods, waste generation per capita per day.
Worked example
A corridor carries 30,000 person trips per day; 40% use transit, 60% use cars with average occupancy 1.5. Car person-trips = 18,000, so vehicles = 12,000 per day. Assume 10% of daily traffic falls in the peak hour: 1,200 vehicles per hour. Two lanes at 1,800 each give capacity 3,600, so v/c = 0.33 - comfortable. Now test the common exam twist: a proposal to add a lane looks unnecessary; a proposal to cut transit share to 30% raises car trips to 21,000 and peak to 1,400 vph, which is still under capacity but changes the LOS assessment and parking demand. Reason with the numbers, not with intuition.
Traps
- Using daily volumes for capacity analysis; capacity is an hourly concept.
- Forgetting occupancy and transit share when converting person-trips to vehicles.
- Designing a road for the peak hour of the peak month without checking the cost of idle capacity.