Travel Demand Appendix B
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TransPlan40 TRAVEL DEMAND APPENDIX B PROCESS Predicting where future transportation the model. Some of the most useful model facilities will be needed is a large outputs to aid in project selection include: undertaking. Changes in land use patterns, political leadership, anticipated ● Origin-Destination flows funding, or a wide range of other factors ● Directional link vehicle volumes can change the dynamics of an area ● Vehicular travel times and speeds and require further study. The development of the Metropolitan ● Transit ridership numbers Transportation Plan occurs over a four- ● AM Travel Peak: 6-8:59 AM year period with an update occurring ● Midday: 9 AM – 2:59 PM every four years. This level of work, as well ● PM Travel Peak: 3-5:59 PM as the frequency of updates, allows Metropolitan Planning Organization ● Evening/Off-peak: 6 PM – 5:59 AM (MPO) staff and decision makers to keep up on emerging trends and course MODEL COVERAGE changes. The process is collaborative. The Until the year 2000, separate travel models MPO works with the county and municipal were maintained for the three urbanized staffs as well as the various transportation areas (Ogden, Salt Lake and Provo). In agencies staffs to produce the plan. The the year 2000, the three urban area following is an overview of the modeling models were combined into one model. process of how projects are developed The coverage has expanded over the and placed in the transportation plan. years to the point that the majority of all of the developable area of Utah, Salt Lake, Davis, and Weber counties is TRAVEL MODEL OVERVIEW covered by the model, with the exception The MPO model process is an integrated of the canyons and the mountains to the land-use, transportation, and air quality east of the urbanized areas. In these model co-developed with the Wasatch cases the population in the areas that are Front Regional Council and is designed to outside of the travel model coverage is perform a wide range of analyses. The relatively small and is separated from the model includes several advanced urban area by some distance. The eastern features that place it on the cutting edge and southwestern portions of Utah County of improved modeling methods required represent a significant percentage of the to satisfy the requirements of the last area, but its mountainous character and federal transportation bill (MAP-21, limited access make it unlikely that it will Moving Ahead for Progress in the 21st need to be incorporated into the Century) and the federal Clean Air Act. In modeled area in the near future. addition, several features recommended by the Travel Model Improvement System-wide transportation planning Program of the US Department of models are typically based on a four-step Transportation, the Federal Highway modeling process: trip generation, trip Administration, the Federal Transit distribution, mode split, and trip Administration and the Environmental assignment. The travel model incorporates Protection Agency are incorporated into these steps and adds an auto ownership model that is sensitive to urban design TransPlan40 | Appendix B Page 1 TransPlan40 TRAVEL DEMAND variables. The model has a feedback loop The travel model is a zonal-based between trip distribution and traffic forecasting tool, modeling travel between assignment. This process ensures aggregate Transportation Analysis Zones consistency between travel congestion (TAZs). The TAZ Structure map shows an and times that influence trip distribution example of the TAZ structure. TAZs cover patterns and are also an outcome of trip the entire model region and don’t TRAVEL MODEL PROCESS assignment. Travel time, or more generally speaking accessibility, is calculated based overlap. There are 2,263 TAZs in the on outputs from the assignment model, modeled region. Land-use and but also is an important determinant of socioeconomic data are summarized trip distribution and mode split. Therefore it within this spatial framework and travel is is customary to iterate these three models estimated between the TAZs. The TAZ in order to reach a convergent solution. Structure Map shows the Wasatch Front region TAZ and highway links structure. TAZ STRUCTURE Base highway and transit networks are created and input into the travel model. The highway network includes all facilities functionally designated as collector or above and some smaller facilities deemed necessary to allow for better model flow. There are approximately 35,000 road links or connections in the network. The transit network is created with local, express, Bus Rapid Transit, Light Rail, and Commuter Rail lines coded in. AND SE ODEL L U M The land use model identifies future land use (i.e. housing and jobs forecasted county-wide by Governor’s Office of Management and Budget) based on accessibility, availability of land (through physical constraints and zoning), and location of existing land uses. This model uses the municipal adopted land uses with the adopted centers identified in Wasatch Choice for 2040 as a land use indicator. Growth is assigned countywide using these adopted parameters. TRAVEL MODEL COMPONENTS At the start of a full model run, the auto- ownership model estimates household auto-ownership levels, then the trip generation model uses land-use data and auto ownership to calculate trip ends at the Transportation Analysis Zone (TAZ) level. These trip ends are then paired into TransPlan40 | Appendix B Page 2 TransPlan40 TRAVEL DEMAND TRAVEL MODEL PROCESS origins and destinations in the distribution each of the trip purposes. Trip model. In the mode split model, a mode generation estimates the number of travel is selected for each trip. Vehicle of trips to and from each TAZ. Trip trips are assigned to the highway network distribution completes the trip by in the assignment model. describing which trip origins are linked with which trip destinations. The travel time feedback loop in the The result of this is a person trip model is accomplished prior to mode matrix for each trip type. Trip choice by converting person trips to distribution links trip-ends of the vehicle trips based on observed data. same type based primarily on the spatial separation of different land The model is comprised of several steps uses and observed sensitivities to with each step programmed or scripted trip length. One output of trip separately. These steps include, but are distribution is the person trip table not limited to the following: for home to work that can be compared to the “Journey-to- Auto Ownership: estimates the Work” data provided by the likelihood of each household in the Bureau of the Census. region having 0, 1, 2, 3+ automobiles. Auto ownership is a Vehicle Assignment: locates the function of the characteristics of a “best” routes between each household and where it is located. origin/destination pair and assigns Auto ownership and availability is a vehicle trips to the highway strong predictor of trip making and network. Important outputs of this mode choice behavior. module include number of vehicles on each roadway segment by Trip Generation: calculates the time period. Several other pieces number of person trips generated of data can be extracted, within each TAZ. The trip including operating speeds, travel generation model parameters are times, Vehicle Miles Traveled (VMT), developed from travel surveys Vehicle Hours Traveled (VHT), and collected in 1993 and 2001. The Volume over Capacity (V/C) on number of trips to and from a roadway links. In addition, one place is a function of the amount can configure the vehicle and types of land-use activity assignment to save all the vehicle within the zone. trips that use a single link in either direction (select link analysis) or all Trip Distribution: pairs the origins the vehicle trips that originate or and destinations for each zone for TransPlan40 | Appendix B Page 3 TransPlan40 TRAVEL DEMAND are destined for a zone (select Model Output: is summarized zone analysis). automatically by the model, including regional statistics (e.g. Travel Time Feedback: finds the VMT, VHT, transit shares and trip best available travel path via each lengths), corridor and segment of the travel modes explicitly performance statistics (e.g. delay, modeled. Several modes are volume, and ridership), district and explicitly modeled, including auto, county-level trip flows, MOVES transit modes (local bus, bus rapid emissions model inputs (EPA air transit, light rail, commuter rail), quality model), and calibration and non-motorized modes. Skims statistics. are reasonable approximations of the travel time and cost between MODEL CALIBRATION all pairs of TAZs, and skims are The model is calibrated to reasonably described for each travel mode. represent 2011 “base year” travel The path-finding algorithms are conditions and patterns, a process in calibrated based on observed which model output is checked or travel paths and observed "validated" against real-world data. Trip relationships between volumes and rates, transit ridership, and highway congested speeds. volumes are examples of types of model outputs that are validated. When the Mode Choice: calculates which model results do not match the base-year mode each person trip is likely to values within an acceptable tolerance, take based on availability and parameters are adjusted until the model is mode-specific parameters (e.g. acceptable. For future forecast years, the time, cost, transit frequency). model output is checked to validate Mode split provides a breakdown model results, allowing model sensitivities of person trips by mode, both for to be assessed. UDOT traffic count data is captive riders (people without used to further calibrate individual automobiles) and for the total corridors. population. The mode split model is developed based on observed data on mode preferences and LAND USE MODELING what those preferences imply Each municipality and the county about sensitivities to mode develop their land use plans as a part of attributes.