Trip Distribution Models in TransCAD. Murtaza Haider Tel: , ext. 2480

Transcription

1 Trip Distribution Models in TransCAD Murtaza Haider Tel: , ext. 2480

2 Trip Distribution Procedures Goal: understand how to use TransCAD to: Generate inputs for trip distribution Run the trip distribution Understand, interpret and analyze procedure results

3 Trip Distribution Trip distribution makes the link between the trips produced by each zone and the trips attracted to each zone Models predict trips for each zone and estimate the flow of trips going from zone i to zone j for all i to j zone pairs The estimated flow of trips going from i to j may depend on the affinity i and j have for each other (e.g. distance, average travel time)

4 Inputs for Trip Distribution Required Zone or point layer joined to balanced productions and attractions for each trip purpose Optional Square matrix of costs of travel between the zones. The IDs of the matrix must match the IDs of the zones

5 Example: Trip Distribution Results

6 Growth Factor Method Scaling an existing matrix by applying multiplicative factors based on input balanced productions (rows) and attractions (columns). In the end, the matrix cells of one row will sum to the row productions and the matrix cells of one column will sum to the column attractions Method sometimes called Iterative Proportional Fitting or Fratar

7 Example: Growth Factor Balancing

8 Getting Ready to Apply a Growth Factor Model Choose File-Close All, then choose File-Open or click on the toolbar. Open the workspace UTOWN_GF.WRK in TCW\TUTORIAL. Choose Planning-Trip Distribution-Growth Factor Method. Choose UTOWN Base OD from the Matrix File drop-down list.

9 Applying the Growth Factor Model Select Production under Constraint Type. Check the Use HBW checkbox. Choose [HBW_P 2000] from the Production Field drop-down list and click OK. Enter MYGFACT as the output filename and click OK. TransCAD applies the growth factor method and generates an output matrix.

10 Growth Factor Application Original data Balanced Matrix

11 Growth Factor Advantages and Limitations Advantages Easy to use No information about transportation network is necessary, thus it is good for short term planning in cases where network is unchanged Limitations Cannot model changes in network well No behavioral explanation behind model

12 Gravity/Entropy Model Operates on the premise that flow between zones decreases as the cost (or impedance) between zones increases Gravity models estimate flows between all zones, given an input matrix of impedances from zone to zone, and balanced vectors of productions and attractions

13 Friction Factors Gravity models generally use measures of relative attractiveness rather than impedances to estimate flow Relative attractiveness is often a function of impedance Popular transformations are gamma, exponential and inverse power functions of impedance Transformations can also be in table format

14 Example: Friction Factors ImpedanceExponentiaInverse Gamma

15 Example: Friction Factor Lookup Table

16 Getting Ready to Create Friction Factors Choose File-Close All, then choose File-Open or click on the toolbar. Open the workspace FRIC_FAC.WRK in TCW\TUTORIAL. Choose Planning-Trip Distribution-Synthetic Friction Factors. Choose Friction Factor Shell from the Matrix File to Fill drop-down list.

17 Entering In Friction Factor Data Check the Use this matrix checkbox. Select Inverse Power under Impedance Function. Enter 1.4 as the value for b. Choose Impedance from the Matrix File drop-down list. Select HBNW FF in the Matrix list.

18 Creating Friction Factors Enter 4.1 as the value for b. Select HBO FF in the Matrix list Enter 3.3 as the value for b and click OK. TransCAD fills the NEWFF matrix file with friction factors and displays a status report. This matrix is now ready to be an input into the Gravity Model.

19 Applying the Gravity Model Required Inputs: Friction factor matrix, or definitions for friction factors Geographic view with balanced productions and attractions for each zone Selection set of zones to be included in output matrix IDs in the friction factor matrix must be the same as the IDs of the zone geographic view Output: Zone-to-zone trip matrix

20 Getting Ready to Apply a Gravity Model Choose File-Close All, then choose File-Open or click on the toolbar. Open the workspace UTOWN_FF.WRK in TCW\TUTORIAL. Choose Planning-Trip Distribution-Gravity Application. In the name field enter HBW Trips Choose HBW_P from the Production drop-down list. Enter 20 for the Iterations.

21 Entering Input to the Gravity Model Click on the Friction Factors tab Choose FRICTFACT Matrix File from the F- Factors drop-down list. Check Use HBW Friction Factor. Click on the General tab Click the Add button In the name field type HBNW Trips Choose HBNW_P from the Production drop-down list.

22 Applying the Gravity Model Click on the Friction Factors tab Selection HBNW Friction in the Matrices list. Click on the General tab Click the Add button Call the third model NHB Trips

23 Applying the Gravity Model Choose NHB_P from the Production drop-down list and click OK. Click on the Friction Factors tab Select NHB Friction in the Matrices list. Check Use NHB Friction Factor. Click OK and enter MYGRAVEV as the output filename. TransCAD evaluates the three models and creates a matrix file with the one matrix for each type of resulting trips (3 matrices).

24 Gravity Model Options Friction Factors Constraint Type K-Factors Extra matrix that is multiplied with the friction factors to adjust and fine-tune the friction factors K-Factor matrices are the same size and contain the same IDs as the friction factor matrices

25 Gravity Calibration #1 The values in a friction factor table or the parameters for an impedance function are often determined from an iterative process This process, called Gravity Calibration, matches the parameters to the Trip Length Distribution (TLD) of observed riders TransCAD provides a Gravity Calibration procedure

26 Gravity Calibration #2 Inputs Base year P-A matrix, impedance matrix, zone layer and selection set Process Initial parameters or friction factor table Apply the gravity model and estimate TLD s Compare TLD s with observed TLD s and change parameters or table as necessary Apply gravity model and compare again

27 Quick Start: Getting Ready to Calibrate Choose File-Close All, then choose File-Open or click on the toolbar. Open the workspace GRAV_CAL.WRK in TCW\TUTORIAL. Choose Planning-Trip Distribution-Gravity Calibration. Choose the matrix file UTOWN Base OD from the Base drop-down list.

28 Entering Inputs Into Gravity Calibration Check the Use HBW checkbox, select Inverse Power under Function, and choose Impedance from the Matrix File drop-down list. Click on HBNW in the scroll list. Check the Use HBNW checkbox, select Inverse Power under Function, and choose Impedance from the File drop-down list. Click on NHB in the scroll list.

29 Calibrating an Impedance Function Check the Use NHB checkbox, select Inverse Power under Function, choose Impedance from the File drop-down list and click OK. Enter MYGRAVCL as the output filename and click OK. TransCAD performs the calibration on the three trip types and estimates the parameters.

30 Gravity Calibration Options Constraint Types TLD Maximum K-Factor Calibration Results in an exact calibration solution, creates a K-factor matrix UTPS-like Calibration Friction factors are weighted by productions, in production constrained calibration, and attractions, in attraction constrained calibration

31 Tri-Proportional Models Doubly-constrained models require that the output flow matrix match input productions and attractions Tri-proportional models add the extra constraint that groups of cells in the output flow matrix must sum to specified values Useful if you know that a sub-area has a known amount of total trips

32 Requirements of Tri-Proportional Gravity Models Friction factor matrix Zone layer with balanced productions and attractions Selection set of zones Zone-to-Zone matrix that contains integer value of the class to which the zone belongs Lookup table of the totals of each class

33 Example: Tri-Proportional Inputs 1. Friction Factor Matrix 2. Zone Layer with Productions and Attractions 3. Matrix of Classes 4. Lookup Table of Total Constrained Trips

34 Example: Tri-Proportional Gravity