Participants reported that models and analytic tools support a variety of activities at their agencies. Due to a variety of institutional relationships, models were sometimes developed by the MPO itself, sometimes with consultant support, and sometimes by the State DOT for use by the MPO. Though some explicit requirements exist for travel modeling to support air quality conformity analysis and Federal Transit Administration (FTA) programs for major transit infrastructure investments (New Starts and Small Starts), the primary application of travel models was for needs determined by each agency without explicit regulatory or program requirements. Primary applications of models and related analytic tools by the peer exchange participants' organizations are discussed in the following paragraphs.
Several participants mentioned that their MPOs were in non-attainment or maintenance areas for air quality. Air quality models, such as the Motor Vehicle Emission Simulator (MOVES)1 offered by the EPA, make use of demand model outputs, and thus indirectly drive the need for travel demand models. However, the air quality issues that affect smaller MPOs are usually driven by larger regional or multi-State conformity concerns, or by the proximity of a much larger metropolitan area with its own MPO and air quality model.
A common role of modeling and analysis is to prepare comparisons between transportation plan alternatives that reflect possible combinations of projects and priorities. In areas with few new projects, and where capacity is adequate for anticipated present and future needs, full regional travel demand modeling may seem unnecessary. Yet every MPO is faced with decisions regarding allocation of funds and resources for project work, operations, and maintenance, and for system policy. Regional travel models can generate baseline system performance measures that can be useful in prioritizing investments other than traditional capacity enhancements. Common measures used in small regional models include average daily traffic and vehicle miles traveled. Regional transportation demand analysis can have an important role to play in supporting economic development and land use planning. The analysis includes questions such as "what development is feasible given the present status of the transportation system, and what would the impacts of such developments be?".
A frequent use of modeling is the evaluation of corridors and proposed projects. Projects might include proposed developments, operations projects and highway construction. "Projects [are] why we do traffic modeling...this includes land development, operations projects, and construction" (Sam Granato, Ohio DOT). Such analyses often includes fairly detailed modeling of small areas, with intersection analysis tools (e.g., Synchro®) and microsimulation tools (e.g., TransModeler®) playing an important role. Visualization tools are also important, with GIS maps frequently being used.
Operational analysis is commonly a significant concern for many small MPOs. Small urban areas are less frequently concerned with large-scale or long-term projects, and planning activities focus on near-term improvements in mobility and accessibility. Such analysis examines a shorter time frame, in which change in demand is a less significant factor. Attention focuses on intersection and roadway configuration updates associated with immediate traffic and development needs. High-quality data about base conditions is very important for the success of such analyses. Where travel demand models are applied, they are often used to supply traffic estimates for capacity and level of service (LOS) analysis at intersections or roadway segments to support design improvements in future years. Non-motorized accessibility is also a concern for some small MPOs, and may be associated with supporting community and economic development.
A number of MPOs expressed interest in land use and economic development. The Champaign-Urbana Regional Planning Commission uses a land use model called Land use Evolution and impact Assessment Model (LEAM)2,that can be linked with travel demand and air quality models. As many small MPOs are in low growth areas, there is general interest in alleviating transportation obstacles to economic development by improving system capacity and removing operational bottlenecks.
The FTA has specific modeling requirements for agencies seeking grants under the New Starts program for major transit investments.3 Applications for New Starts funding require credible travel forecasts. These forecasts are typically developed via travel demand models that are grounded in current planning data. While few small MPOs enter the New Starts program (and none of the peer exchange participants had done so), other FTA programs such as the Small Starts or Very Small Starts also have analytic requirements, and may be served by models, though a full-blown mode choice model may not be necessary. Other options may include using a pivot-point model (estimating changes in mode share from baseline conditions), the EPA Commuter model4, or TCRP Synthesis 66 on "Fixed-Route Transit Ridership Forecasting and Service Planning Methods."5 As noted later in this report, several of the peer exchange participants felt that transit modeling simply increased model complexity without providing commensurate benefits. Few of the agencies in the peer exchange maintained transit components in their models, though some were considering doing so. Whether or not to support transit modeling is thus a local decision based on the specific needs of each MPO.
Participants in the peer exchange noted that a regional travel demand model may not always be a central tool to support planning functions. For MPOs in areas with low growth and little transit use, one participant (Joseph Nigg, Fargo, ND) asked "Do you need a model? Why is this so important to the functioning of a region? There are other factors beyond traffic volumes that may be more important for project evaluation, such as economic impact, land use, or safety."
Regional models are most suitable for analyzing growth in daily traffic and vehicle miles due to growth in internal demand. External demand and through traffic may be accounted for but are not generated within such models. Project evaluation may involve additional measures for which regional demand models are unsuited or insufficient. Such measures may include land use and economic development considerations (for example, studying access to a potential intermodal transfer facility). Safety impacts are another area of rising concern. Operational concerns such as bottlenecks or congestion limitations may be more effectively addressed through corridor microsimulation. Because these concerns are typically analyzed relative to present-day needs and seek rapid analysis results, the time frame addressed in the analysis of such issues is often shorter than in a regional model (looking out two to five years, rather than twenty or twenty-five). Consequently, they may be addressed effectively through simulation tools or highway capacity analysis rather than demand models, using traffic growth estimates from trend analysis, or trip generation estimates based on new land uses. Models are necessary when it is important to understand traveler response to system changes. Where demand is already understood for a facility or small sub-area, deterministic methods such as microsimulation will provide greater understanding of operational performance.
Even with relatively large projects in small urban areas, the project cost and risk may be too low to warrant the expense of a full analysis with a demand model. The peer exchange participants were in agreement that a regional travel demand model serves as one tool among many, rather than playing a central role as at many larger MPOs.
2 More information on LEAM: http://www.leamgroup.com/technology/regional-modeling/leam-land-use-model (Accessed 6/22/2012)
4 Information the COMMUTER model and related resources: http://www3.epa.gov/otaq/stateresources/policy/pag_transp.htm#cp (Accessed 7/5/2012)
5 http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_syn_66.pdf (Accessed 7/5/2012)