Travel Demand Forecasting Traffic Assignment CE 331 Transportation

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Travel Demand Forecasting: Traffic Assignment CE 331 Transportation Engineering

Travel Demand Forecasting: Traffic Assignment CE 331 Transportation Engineering

Overall Procedure Land Use and Socioeconomic Projections Trip Generation Trip Distribution Modal Split Traffic

Overall Procedure Land Use and Socioeconomic Projections Trip Generation Trip Distribution Modal Split Traffic Assignment Direct User Impacts Transportation System Specifications

Traffic Assignment ¢ What route to choose? l l ¢ Input l l l

Traffic Assignment ¢ What route to choose? l l ¢ Input l l l ¢ Mostly for auto mode Intermodal network OD matrix by mode Roadway network (for auto) and/or transit network Characteristics (travel time, cost, …) of each route connecting an OD pair Output l Vehicular flow on each link of the network

Assignment Techniques ¢ Basic Assumption l ¢ Travelers always choose the least cost route

Assignment Techniques ¢ Basic Assumption l ¢ Travelers always choose the least cost route connecting the OD All or nothing assignment Assign all trips/vehicles to the route with minimum cost l Assume travel time does not change with volume l ¢ Equilibrium assignment

All or Nothing Assignment 10 min 600 veh 600 O D 12 min 0

All or Nothing Assignment 10 min 600 veh 600 O D 12 min 0 veh If there are 600 vehicles traveling between O and D, all of them will be assigned to the shortest route (with 10 min travel time).

Problems of “All or Nothing” Assignment Ignore capacity constraint ¢ Ignore the fact that

Problems of “All or Nothing” Assignment Ignore capacity constraint ¢ Ignore the fact that travel time is related to flow level ¢

Highway Performance Function ¢ Flow-dependent travel time l l Free flow travel time (tf)

Highway Performance Function ¢ Flow-dependent travel time l l Free flow travel time (tf) Typical form: a. k. a. BPR function

Equilibrium Assignment ¢ Basic Assumptions Travelers know the exact cost of choosing each route

Equilibrium Assignment ¢ Basic Assumptions Travelers know the exact cost of choosing each route l Travelers always choose the routes that minimize their own travel cost l

User Equilibrium Model travelers’ route choice behavior ¢ Equilibrium condition: ¢ l Between an

User Equilibrium Model travelers’ route choice behavior ¢ Equilibrium condition: ¢ l Between an OD pair, • All used routes will have the same travel time; • All unused routes will have longer travel time(s).

Example 1 t 1 = 6 + 4 x 1 (thousand vehs) 4500 O

Example 1 t 1 = 6 + 4 x 1 (thousand vehs) 4500 O D t 2 = 4 + x 22 x 2 (thousand vehs) At equilibrium, let t 1 = t 2 6 + 4 x 1 = 4 + x 22 x 1 + x 2 = 4. 5 x 1 = 1. 6 x 2 = 2. 9

Population, Household by TAZ – Woodford County

Population, Household by TAZ – Woodford County

Estimated Speed

Estimated Speed

Congestion Level (V/C ratio) Estimation

Congestion Level (V/C ratio) Estimation