Traditional Four-steps Transportation Forecasting Model

1. Basic Knowledge of Transportation Planning (2) Lectures 17Mode Choice & Trip Assignment(Chapter 8, Textbook)

2. Traditional Four-steps Transportation Forecasting Model Trip Generation Trip Distribution Mode Choice Trip Assignment

3. Mode Choice (Mode Split) – Purpose • To determine how many trips are made by different modes available in the urban area (QIJK, number of trips between zones I and J made by mode K)

4. Mode Choice – Factors Affecting the Choices (1) • Characteristics of the trip • - Trip purpose • - Trip length • - Time of day • Characteristics of trip maker • - Income • - Auto availability • - Age

5. Mode Choice – Factors Affecting the Choices (2) • Comfort and convenience • Walking distance • Number of transfers/reliability • Physical comfort (weather protection, temperature, etc.) • Psychologies factors (status, privacy, etc.) • Amenities (beverage, food service) • Feeling of security Characteristics of the modes - Line haul time - Transfer time - Walk time – within ¼ mile - Wait time - Frequency of service - Schedule - Reliability (variance in time) - Access and egress time Cost to users - Fares - Tolls - Parking - Fuel - Fixed costs (insurance, depreciation, etc.)

6. Mode Choice – Models • The dependent variable of the mode choice model would be the market share or the percent of travelers that are expected to use each of the available modes • The independent variables are factors that affect the mode choice of trip makers

7. Mode Choice – Utility and Disutility Functions • A utility function measures the degrees of satisfaction that people derive from their choice • A disutility function represents the generalized cost (akin to the concept of impedance) that is associated with each choice.

8. Mode Choice – Utility and Disutility Functions • The utility (or disutility) function is typically expressed as the linear weighted sum of the independent variables of their transformation; that is, • U = a0 +a1X1 +a2 X2+ … + arXr • where U is the utility/disutility derived from a choice defined by the magnitudes of the attributes X that are present in that choice and weighted by the model parameters ai

9. Mode Choice – Multinominal Logit Model • The multinomial logit model calculates the probability of choosing mode K if disaggregate or the proportion of travelers in the aggregate case that will select a specific mode K according to the following relationship: • This specification ensures that all trips that have been estimated to occur on a specific interchange are assigned to the available modes; that is, the following trip balance equation is satisfied:

10. Mode Choice – Example (1) Example: Three mode choices: Car (C), Bus (B), Train (T) Factors affecting mode selection: Household income (IN) Trip cost (TC) Trip time (TT) Utility functions: By car By bus By transit

11. Mode Choice – Example (2) The probability for a traveler k to select modal m :

12. Example 8.6 – Application of Logit Model

13. Solution of Example 8.6 – Application of Logit Model

14. Trip Assignment - Purpose • Given QIJK, that is, the estimate of interzonal demand by mode, determine the trip-maker’s likely choice of paths between all zone I and J along the network of each mode K and predict the resulting flows q on the individual links that make up the network of that mode

15. Trip Assignment - Rationale • The estimates of link utilization can be used to assess the likely level of service and to anticipate potential capacity problems • The number of available paths between any pair of zones depends on the mode of travel • In the case of private transportation modes a driver has a relatively large set of possible paths and path variations and also a good deal of freedom in selecting between them • On the other hand, typical mass transit modes offer a limited number of path (or route) choices

16. Trip Assignment – Link flow and Interzonal Flows • Interzonal flows (QIJ) refer to the demand for travel between a pair of zones • Link flows (qij) refer to the flow that occurs on a specific link (i, j) of the transportation network and is the sum of all interzonal flows that happen to include that particular link on their preferred paths

17. Trip Assignment – Stochastic Equilibrium • Users have only limited information about the network and their transportation options for going from an origin to a destination. • Instead of basing the equilibrium on “general cost”, it is more logical to base it on the perceptionsof users. • I.e. user assigns himself/herself on a path that he or she thinks is the shortest.

18. Trip Assignment – Major Steps • Step 1: Describe the network (provide a way of coding network) • Step 2: For each zonal interchange, impedances on alternative routes computed • Step 3: Based on particular assignment rule, trips are assigned to particular routes

19. Trip Assignment Inputs and Outputs

20. Trip Assignment – Deterministic Models • Concept of Shortest Path • Free-All-or-Nothing Traffic Assignment • Free/Multipath Traffic Assignment • Apply the MultinormialLogit Model (MNL) • with the negative of path utilities in place of the utility terms • Capacity-Restrained Traffic Assignment

21. Example– All-or-Nothing Assignment Simply assumes that all of the traffic between a particular origin and destination will take the shortest path (with respect to time)

22. Highway Network:

24. Example 8.15 – Free/Multipath Traffic Assignment Note:

25. Homework #7 – Examples 8.3 and 8.7, Due: 3:30 PM on July 5 Example 8.3 – see Slides 34 – 38 (Lecture 16) Example 8.7