Metropolitan Travel Forecasting Current Practice and Future Direction -- Special Report 288 (2007) / Chapter Skim
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6 Advancing the State of the Practice
6 Advancing the State of the Practice
Pages 90-121
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From page 90... ...
This chapter addresses in turn improvements in four-step trip-based modeling; advanced modeling practices; the TRANSIMS system; experience with advanced practice; obstacles to model improvement; and model research, development, and implementation. IMPROVEMENTS IN FOUR-STEP TRIP-BASED MODELING Many improvements in the four-step process can be and have been made.
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From page 91... ...
Newer approaches now used by some MPOs estimate congestion on the basis of modeled delay at arterial intersections. • Inclusion of both highway and transit travel in trip distribution: Trip distribution, the second step in the four-step process, involves allocating travel among analysis zones.
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From page 92... ...
Rather, a suite of related approaches, taken together, shows promise for greatly improving modeling practice. These approaches are referred to here as "advanced modeling practices" or advanced models.
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From page 93... ...
To address user needs: Simulation of development probability by parcel or grid cell, with consideration of floor space prices and vacancy. Goods movement/ Current practice: Simple truck model.
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From page 94... ...
To address user needs: Tour-based destination choice, with intermedi ate stops. Mode choice Current practice: Trip-based, with nonmotorized modes.
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From page 95... ...
Land use models have a long history of evolution and application in the United States and elsewhere. A recent innovation is the acceptance and use of "integrated urban models" that combine advanced land use and transportation models to better represent the interactions between transportation and land use.
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From page 96... ...
. While there can be benefits to aggrega tion when all aspects of decision processes cannot be accounted for, model results will be improved to the extent that model sets can more clearly repre sent both choices available to travelers and decision factors relevant to indi vidual travelers.
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From page 97... ...
. Traffic microsimulation can be combined with an activity-based travel demand model to provide a powerful tool for forecasting and analyzing supply-side transportation system and facility performance.
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From page 98... ...
. TRANSIMS incorporates and integrates some of the advanced modeling practices detailed above, in particular population synthesis, activity-based modeling, and traffic microsimulation.
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From page 99... ...
The extent and cost of necessary data collection, computer hardware requirements, and the complexity of implementation have been exaggerated. Implementing such a new model set does require more data, staff resources, and computing power than continuing to use existing technology, but it is demonstrably achievable (see "Experience with Advanced Practice" below)
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From page 100... ...
The current state of knowledge is such that there can be no definitive answer to these questions, but the following discussion of field experience with advanced practice models should shed some light. The following three agencies in North America have implemented advanced activity-based travel models and are using them in practice (VHB 2006)
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From page 101... ...
Mid-Ohio Region Travel Demand Model This new set of regional travel forecasting models for MORPC was completed in 2004. It is described as an advanced, multistep tour-based microsimulation model (Anderson and Donnelly 2005)
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From page 102... ...
Because of the high standards set by FTA for travel demand modeling for New Starts, the performance of the MORPC model for this transit study was evaluated with some care (Schmitt 2006)
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. San Francisco County Transportation Authority The San Francisco County activity-based model was developed to provide more detailed and accurate information on traveler behavior with respect to destination choices, modal options, and time of day.
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From page 104... ...
Cost Cost is one potential barrier to the implementation of advanced modeling practices. The cost of implementing an activity-based model depends on a number of variables, including the size of the network, the extent of transit service, and the availability of activity information from a recent home inter view survey.
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From page 105... ...
Given the work involved in revising forecasts, agencies may be reluctant to change models once the model emissions budget within the state implementation plan has been established.
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From page 106... ...
Lacking such retrospective analysis that demonstrates a failure of current forecasting procedures, agencies are under little pressure to devote resources to the exploration or development of new procedures. Second, proof that the advanced modeling practices are better than current practices is needed.
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From page 107... ...
cities are known to have implemented such advanced models, and eight others are in the design process. While some MPOs are satisfied with the status quo, it is apparent that there is a growing willingness to adopt or at least explore advanced practices that may better serve MPOs with more complex needs.
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From page 108... ...
. A 2003 performance assessment found that TMIP had had a positive influence on short-term model improvements, leaving transportation agen cies in a better position to address federal and state planning requirements.
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From page 109... ...
Examples are the completed NCHRP Report 388: A Guidebook for Forecasting Freight Transportation Demand and two efforts currently under way: NCHRP Projects 8-37, Standardized Procedures for Personal Travel Surveys, and 8-61, Travel Demand Forecasting, Parameters and Techniques.2 In the past, NCHRP funding has been programmed to support specific TMIP activities. Other Research and Development Initiatives Other sources of funding and research to advance the state of practice in travel modeling include the national Transit Cooperative Research Program (TCRP)
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From page 110... ...
Examples are the com pleted TCRP Report 48: Integrated Urban Models for Simulation of Transit and Land Use Policies: Guidelines for Implementation and Use and the in progress TCRP Project H-37, Improving Travel Forecast Models for New Starts -- Mode Specific Constants. University researchers can also make substantial contributions to research and practice, working with MPOs and states.
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From page 111... ...
Each MPO must find its own funding, data, consultant assistance, and trained staff for model development. To the extent that metropolitan areas have their own unique conditions, this may be appropriate.
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There are also national models for how entities with common research interests can benefit from pool-funded research: NCHRP for state transportation agencies, TCRP for transit agencies, the Airport Cooperative Research Program (ACRP) for airports, the National Cooperative Freight Research Program (NCFRP)
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From page 113... ...
advanced models, with sensitivity and validation tests; • Exploration of data and parameters transferable from region to region; • Development of universally estimated, locally calibrated models; • Pooled acquisition of computer software and hardware; and • Documentation of practice for shared-use applications. An Integrated Approach to Research, Development, and Implementation of Advanced Models Currently, elements of research, development, and implementation for travel models are diffused among local, state, and federal governments and other entities.
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From page 114... ...
SUMMARY FINDINGS AND RECOMMENDATIONS This chapter has addressed improvements in four-step trip-based modeling; advanced modeling practices; TRANSIMS; experience with advanced prac tice; obstacles to model improvement; and model research, development, and implementation. Improvements in Four-Step Trip-Based Modeling MPOs may undertake ambitious modeling improvement programs within the framework of their current models.
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From page 115... ...
For this reason, the committee believes that MPOs experimenting with or fully implementing advanced modeling practices should document their experiences, including costs, advantages, drawbacks, and any transferable data or model components. In addition, the committee recommends that studies be performed to compare the performance of conventional and advanced models and to evaluate how well-implemented advanced models handle complex planning issues that are beyond the scope of current models.
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From page 116... ...
cities are actively planning for the introduction of advanced models. Obstacles to Model Improvement Obstacles to the adoption of advanced modeling practices include the following: • Cost of implementation, • Limited staff skills, • Reluctance to suggest problems with existing models since doing so could cause projects planned on the basis of those models to be challenged, • Reluctance to change models once the model emissions budget within the state implementation plan has been established, • No analysis demonstrating a weakness of current forecasting procedures,
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From page 117... ...
A 2003 performance assessment found that TMIP had a strong positive influence on short-term model improvements. Successes have included enhancements to current models, topical conferences and workshops, a newsletter, a website, an e-mail list that reaches a national and international audience, and a travel model peer review program.
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NCHRP conducts research on topics directly related to metropolitan travel forecasting. Other Research and Development Initiatives Other sources of funding and research support efforts to advance the state of practice in travel modeling.
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From page 119... ...
This cooperation could be accomplished through a national travel forecasting steering committee. This committee could set goals and an agenda for joint activities aimed at improving travel models and modeling practice.
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From page 120... ...
2005. Las Vegas Travel Demand Model Guidelines for Estimation, Calibration and Validation.
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From page 121... ...
2006. Results of FY2006 Travel Forecasting Research, Task 5: Review of Current Use of Activity-Based Modeling.
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