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Norman Washington G arrick CE 2710 Spring 2014 Lecture 07

Transportation Forecasting Trip Generation. Norman Washington G arrick CE 2710 Spring 2014 Lecture 07. The Four Step Model. Trip Generation Estimates the number of trips from given origins and destinations Trip Distribution

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Norman Washington G arrick CE 2710 Spring 2014 Lecture 07

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  1. Transportation Forecasting Trip Generation Norman Washington GarrickCE 2710 Spring 2014 Lecture 07

  2. The Four Step Model • Trip Generation Estimates the number of trips from given origins and destinations • Trip Distribution Determines the destination for each trip from a given origin • Mode Choice Determines the mode choice for each trip • Route Assignment Determines the specific route for each trip

  3. 1 3 2 5 4 8 7 6 Trip Generation Trip Generation model is used to estimate the number of person-trips that will begin or end in a given traffic analysis zone (TAZ) The unit of analysis for traffic generation is the TAZ

  4. Estimated Target year socio-economic, land use data Predict Target year No. of Trips Calibrated Model Relating trip making to socio-economic and land use data Trip GenerationDeveloping and Using the Model Survey Base Year Socio-economic, land use and Trip making

  5. Trip GenerationForm of the Model The trip generation model typically can take the form of No. of trips = Function (population, income, auto ownership rates) The model is developed and calibrated using the BASE year data

  6. Trip GenerationTravel Survey Trip Generation models are often developed from travel surveys. These surveys are used to determine the trip making pattern for a sampling of households in the area. This trip making pattern is then related to land use and socioeconomic factors that are considered to affect travel patterns Common socioeconomic factors considered include population, income, and auto ownership rates

  7. Trip GenerationTrip Purpose Often separate predictions are mode for different type of trips since travel behavior depends on trip purpose In other words different models must be developed for each trip type The category of trip types commonly used include • Work trips • School trips • Shopping trips • Recreational trips

  8. Trip GenerationExample of a Trip Generation Model One way of presenting the trip generation model developed from a survey is as a cross-classification table

  9. Calibrated Model Relating trip making to socio-economic and land use data Trip GenerationThe Survey and The Model Survey Base Year Socio-economic, land use And Trip making

  10. Trip GenerationTrip Rates

  11. Trip GenerationTrip Rates

  12. Trip GenerationTrip Rates

  13. Trip GenerationTrip Rates

  14. Trip GenerationTrip Rates

  15. Estimated Target year socio-economic, land use data Calibrated Model Relating trip making to socio-economic and land use data Trip GenerationEstimating Target Year Data

  16. Trip GenerationTarget Year Data

  17. Trip GenerationTarget Year Data

  18. Trip GenerationTarget Year Data

  19. Estimated Target year socio-economic, land use data Predict Target year No. of Trips Calibrated Model Relating trip making to socio-economic and land use data Trip GenerationPredicting Number of Trips

  20. Trip GenerationPredicting Number of Trips 60 Number of Trips = trip rate*no. of HH = 0.6 * 100 = 60

  21. Trip GenerationPredicting Number of Trips

  22. Trip GenerationPlanning for the Future and Uncertainties Earlier we talked about the uncertainties associated with making prediction for the future and the importance of not treating predictions as if they are set in stone but rather as a guide to help in decision making In considering the ‘trip generation’ process it is important to understand some potential sources of uncertainties

  23. Trip GenerationSources of Uncertainties in Predicting Number of Trips Significant errors can creep into the trip generation process in a number of places including • Errors in the survey Who is surveyed, how well was the survey constructed, did we consider all important parameters? • Errors in the prediction of future demographics Will the population grew, what will be the make up of the population • Errors in how well the model can actually reflect the future Will the land use change, will transportation change, will technology change, will peoples attitudes change

  24. Trip GenerationEffect of Changes in Land Use Changes in Land use and the type of transportation provided can have a huge impact on travel But the trip generation process typically assume that this factor is constant over the period of the study

  25. Trip GenerationDemographics and Trip Making Factors affected by Land Use The land use pattern and transportation type may affect • Car ownership rates • Household size and composition • Number of daily trips • Mode of trips • Length of trips

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