National Academies Press: OpenBook
« Previous: T56712 Text_50
Page 59
Suggested Citation:"T56712 Text_51." National Academies of Sciences, Engineering, and Medicine. 2008. Innovations in Travel Demand Modeling, Volume 1: Session Summaries. Washington, DC: The National Academies Press. doi: 10.17226/13676.
×
Page 59

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

idation process will include model estimation tests and model application tests. The anticipated validation tests for the model components include (a) checks to ensure that the model component is producing the correct results, (b) com- parisons of model parameters to comparable parameters in similar models in other areas, (c) disaggregate validation of all model components, (d) testing of each model’s sensitiv- ity to variables through controlled modification of those input variables, (e) comparisons of the model component output to the results from the survey data set, and (f) com- parisons of base year outputs from model components to available independent observed data. • The second set of tests will focus on model appli- cations. The model application tests will address aggre- gate comparisons to the Travel Behavior Inventory (TBI) survey results, comparisons to independent data, and assessments of the individual model components. • A number of issues may need to be addressed in developing and conducting validation tests of new activity- based models. Possible issues include the lack of experience with activity- based models and available comparisons and the lack of established standards, acceptable error ranges, and elasticity standards. Other possible issues may emerge during the aggregate comparison to the TBI survey results and the aggregate comparison to independent data. • The overall model validation will be performed for the model estimation year 1997 and for 2005 against independent observed data. Examples of elements to be included in these traditional checks are the root- mean- square error of modeled to observed traffic volumes, matching observed vehicle miles of travel with approxi- mately 1% error, matching highway and transit screen- line volumes, and matching total transit boardings. Other traditional checks include park- and- ride lot usage, matching of peak and off- peak roadway speeds, toll road usage, and highway volumes on individual freeways. • The validation process includes validating the new model against observed travel data for 1997 and 2005. While these tests are important for model validation, they do not address the potential true value of activity- based models, which is the ability to provide better assessments and travel forecasts based on a more appro- priate representation of the actual decision- making process. Two approaches will be used to test the sensitiv- ity of the activity- based model. • The first approach for testing the sensitivity of the new activity- based model will be to compare the forecast year results to those results obtained by the calibrated trip- based model. The second approach will focus on develop- ing a model that is more sensitive to policy variables. These policy- oriented tests, which will be subjective, will include evaluating transit- oriented development areas, dif- ferent regional development densities, development in known industrial areas, development of specific greenfield areas, and redevelopment efforts in targeted areas. VALIDATION AND ASSESSMENT OF ACTIVITY- BASED TRAVEL DEMAND MODELING SYSTEMS Ram Pendyala and Chandra Bhat Ram Pendyala discussed validation and assessment of activity- based travel demand models. He described vari- ous approaches to validating and assessing activity- based models, potential issues, and topics for further consider- ation. Volume 2 contains a paper on the topic.2 The fol- lowing points were covered in his presentation. • While there continues to be growing interest in the use of activity- based travel models, actual application of these models has been limited. The lack of detailed vali- dation and assessment of these new models may be a contributing factor to their slow introduction. Given the costs associated with the new models, information on their benefits is needed for widespread use. • Validation of travel demand models typically involves the refinement and adjustment of model com- ponents and parameters to ensure that the forecasts repli- cate base- year travel conditions and statistics within an acceptable margin of error. Examples of measures fre- quently used in the validation process include aggregate measures of travel such as vehicle miles traveled (VMT), vehicle hours traveled, mode split, trip length distribu- tion, and total trips and trip rates. The traditional approach has focused on replicating observed base- year conditions within a certain margin of acceptable error. • At a basic level, validation of activity- based travel models will focus on replicating base- year travel condi- tions comparable to those achieved with existing four- step models. A number of issues may need to be addressed in validating new models. There may be an expectation that a higher standard of validation should be used with activity- based models and that fewer adjustments and refinements will be needed. Currently, there is an absence of performance assessment standards for validating activity- based models. There is a need to develop techniques and approaches for comparing the results from traditional four- step models with the results from activity- based models. • While it is important to consider the accuracy of replicating base- year conditions, one of the benefits of activity- based models is their use in analyzing a wide range of policies and scenarios. To address these elements, an assessment of an activity- based model might focus on a variety of policies and scenarios. Examples might include examining changes in land use, socioeconomic 51VALIDATION 2 See Pendyala, R. M., and C. R. Bhat. Validation and Assessment of Activity- Based Travel Demand Modeling Systems. Volume 2, pp. 157–160.

Next: T56712 Text_52 »
Innovations in Travel Demand Modeling, Volume 1: Session Summaries Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB Conference Proceedings 42, Innovations in Travel Demand Modeling, Volume 1: Session Summaries summarizes the sessions of a May 21-23, 2006, conference that examined advances in travel demand modeling, explored the opportunities and the challenges associated with the implementation of advanced travel models, and reviewed the skills and training necessary to apply new modeling techniques.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!