Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 120


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 119
119 8.11 Case Study Oregon called for the director of ODOT to appoint members to the Statewide Passenger committee to advise the director and Oregon Transportation and Freight Forecasting Commission on issues, policies, and programs that impact Model multimodal freight mobility in Oregon. This included iden- tifying high-priority freight mobility projects for considera- Background tion in Transportation Improvement Programs. Context Objective and Purpose of the Model Goods movement by truck is a vital component of Ore- gon's economy. On an average weekday, approximately In 1996, the State of Oregon, through ODOT, established 780,000 tons of goods worth $486 million are transported the Transportation and Land Use Model Integration Pro- on Oregon state highways. Goods from Washington State gram (TLUMIP) to prepare legislation and guidelines for make up the largest inbound shipments, reflecting the geo- travel demand and land use planning. The program devel- graphic proximity of Portland to Seattle and Spokane. oped and refined an interactive statewide transportation and Goods from California also make up a large share of land use model for use in transportation planning and policy inbound shipments. Together, Washington and California analysis at varying scales of geography. The model covered account for over three-quarters of all inbound truck ship- the entire State of Oregon, and it complemented all MPO ments to Oregon, while the Mountain Pacific, Midwest, and models. It simulated land use and travel behavior math- Southern regions of the United States make up approxi- ematically, relying on various data sources. In early 1999, mately 11%. ODOT began developing the second generation statewide As shown in Table 8.50, truck traffic in Oregon is expected model. The second Transportation and Land Use Model to grow significantly over the next 20 years. The Oregon Integration Program (TLUMIP2) integrates both passenger Department of Transportation (ODOT) is aware of the cru- travel and freight movements, simultaneously modeling land cial role freight transportation plays in the state's economy. use, economic activity, transportation supply, and travel In 1995, ODOT initiated the Oregon Model Improvement demand. Program (OMIP) to address the relationship between trans- The new Oregon Statewide Model can be used to 1) portation, land use, and economics. Under OMIP, all Oregon analyze and support land use and transportation decision- cities, counties, MPOs, and state agencies work together using making; and 2) make periodic, long-term economic, demo- state-of-the-art transportation modeling tools for application graphic, passenger, and commodity flow forecasts at the in statewide, urban, and small city model areas. statewide and substate levels. Specifically, it can be used to The area covered by the Oregon model is shown in Fig- analyze the potential effects of transportation and land use ure 8.24. policies, plans, programs, and projects on travel behavior and In 1998, ODOT formed the Oregon Freight Advisory location choices. The model produces outputs that can be Committee (OFAC). In 2001, the Oregon State Legislature used in other analysis packages for assessing transportation formalized OFAC by passing House Bill 3364. This legislation system performance. Table 8.50. Freight shipments to, from, and within Oregon (1998, 2010, and 2020). Tons (Millions) Value (Billions of Dollars) Oregon 1998 2010 2020 1998 2010 2020 State Total 291 428 557 201 411 704 By Mode Air <1 <1 1 15 42 85 Highway 220 323 420 165 330 555 Other 2 3 4 <1 <1 <1 Rail 53 81 109 18 34 55 Water 16 20 24 3 5 8 Source: U.S. Highway Administration Office of Operations, Freight News, November 2002.

OCR for page 119
120 Source: ESRI 2002, prepared by Cambridge Systematics, Inc. Figure 8.24. Oregon Statewide Model. The second generation model includes several important class models develop modal facility flows by assigning modal characteristics not found in the first generation. This new O-D tables of commodity flows to modal networks. The zonal model: employment or economic activity is not directly supplied to the model but is created by applying an economic/land use Operates at a single geographic scale, using traffic analysis model. The O-D table, produced by applying commodity trip zones within the urban areas and larger zones outside; generation and distribution steps to the resulting employment Fully integrates the economic, land use, and transportation O-D table, is split to freight modes based on existing shares or model elements; a diversion method. A detailed description of the economic Is dynamic; activity class of model is provided in Section 6.5. Is a hybrid equilibrium (for economic and transportation As shown in Figure 8.25, the Oregon model contains a set markets) and disequilibrium (for activity and location of seven separate but highly connected modules: regional economics and demographics; production allocations and markets) formulation; and interactions; household allocations; land development; com- Is an activity-based travel model. mercial movements; household travel; and transportation supply. As of this writing, the second generation Oregon Statewide Model has not been validated or applied, but is described in REGIONAL ECONOMICS AND DEMOGRAPHICS the following sections of this case study. The regional economics and demographics module pro- vides productions in each economic sector, imports and ex- General Approach ports by economic sector, employment by labor category, and in-migration and payroll by sector for each year. The produc- Model Class tion sectors in the model follow conventional industry break- The Oregon Statewide Model is an economic class of model downs. Besides the production sectors, Oregon's model has designed for forecasting both passenger and freight move- four sectors for final demand: exports, consumption, invest- ments. In contrast to four-step commodity models, economic ment, and government (state and local).

OCR for page 119
121 Regional Economics and Demographics Production Allocations Transport Supply and Interactions Household Travel Data Store Household Allocations Commercial Movements Land Development Source: J.D. Hunt and others, Design of a Statewide Land Use Transportation Interaction Model for Oregon, 2001. Figure 8.25. Modules in the Oregon Statewide Model. PRODUCTION ALLOCATIONS AND INTERACTIONS COMMERCIAL MOVEMENTS The production allocations and interactions model deter- The commercial movement module is used to determine mines the distribution of production activity among zones, the the growth of truck movements during a particular workday consumption of space by these production activities, the flows in each year. It synthesizes a fully disaggregated list of individ- of goods and services and labor from the location (zone) of pro- ual truck movements. For each truck movement, the synthe- duction to the location (zone) of consumption, and the ex- sized data are the vehicle type (light single-unit, heavy single- change prices for goods and services, labor, and space each year. unit, articulated), starting link, ending link, starting time, The model also uses the concept of exchange locations, the commodity carried and transshipment organization. Ship- places where commodities transfer between seller and buyer. ment sizes are chosen to be consistent with the CFS. A value to weight ratio is necessary to calculate the weight of each ship- ment. The aggregate flows in the activity interaction matrices HOUSEHOLD ALLOCATIONS are first translated into discrete shipments by commodity, During the allocation of production activities, households then combined into truck tours. O-D patterns for empty ve- stay in the zones in which they were placed by the household hicles are derived from the patterns for loaded vehicles. allocation module the previous year. The labor flows produced by these households are allocated to the exchange locations as HOUSEHOLD TRAVEL part of the allocation of production activities. Similarly, the flows of commodities consumed by the households are allo- The household travel module establishes a list of the specific cated from the exchange locations. individual trips made by members of households during a par- ticular representative workday for each year, providing starting link, end link, starting time, tour mode, vehicle occupancy, util- LAND DEVELOPMENT ity attribute coefficients, and non-network-related utility com- The land development module determines the changes in ponents. The process starts by assigning each household mem- space from one year to the next. The supply of space in a par- ber an activity pattern for the day. The activity pattern is a listing ticular year is fixed, and the other modules operating for the of the sequence of activities undertaken by the household mem- year take into account this fixed supply. These other compo- ber as a series of tours made out from the home or work place. nents determine a price for each category of space in each zone, and the primary task of the land development module TRANSPORT SUPPLY is to adjust the quantity of space over time in response to changes in price. This is done in a highly disaggregate man- The transportation supply module is a hybrid of macro- ner, one grid cell at a time. scopic and microscopic techniques. Equilibrium travel times

OCR for page 119
122 are found by loading a conventional trip table to a network. Framework These equilibrium travel times then are used in a microscopic assignment, which works at the level of individual vehicles, This is a statewide passenger and freight forecasting model. determining the network loadings from synthesized demands Both passenger and freight vehicles are forecast and assigned of the household travel and commercial movements. simultaneously. The goods and services shipments flows are determined as part of the spatial distributions of activities and population, Flow Units following the path from the production locations to the The model estimates O-D table of commodity flows and exchange locations and then to the consumption locations. then converts to freight trucks before assignment. Mode split and assignment are accomplished together as a simultaneous loading to a multimodal network. The multi- modal network represents the supply of various combina- Data tions of available goods and services. Apart from the model modules, the principal components Forecasting Data of the software system for running the model are data store, The state and the MPOs develop and maintain the data- process control, user interface, and calibrator. bases needed to produce future year forecasts to support travel demand modeling, land use allocation models, and The data store is the database in which all the information policy analysis as required under Federal guides and the input and output from the modules is stored. All informa- statewide planning program. These databases and forecasts tion flowing between modules passes through the data store. support statewide planning for intrastate freight and passen- The process controller commands the operational sequence ger movements and distribution of population and employ- of each of the modules in order to facilitate model run. In a ment growth. The forecasts are sufficiently detailed to given year, the economic and demographic module is run provide control totals to city and county planning agencies first, followed by the production allocation and interactions for use in developing and applying land use allocation mod- module, and so on following a clockwise circuit as shown in els, and travel demand and freight models. Figure 8.25. This model operates at three geographic levels: statewide, The user interface includes a graphic interface for facilitat- substate, and urban. The statewide model assesses broad pol- ing both input and output. With the graphic interface, in- icy options and intercity travel and provides the basis for the puts are written to the data store and specified outputs substate model. The regional substate model offers a finer from the data store are presented in graphical or map for- level of analysis along the major transportation corridors. mat as appropriate. Finally, the urban model handles the high-resolution analy- The calibrator facilitates the estimation of specified model sis of the local impacts of policy decisions and investments. parameters given various observations of systems behav- The regional economics and demographics module pro- iors, considering the fit of the model across modules. vides productions in each economic sector, imports and exports by economic sectors, employment by labor cate- gory, and in-migration and payroll by sector for each year. Modes This module uses United States gross domestic product, The Oregon model assigns modal O-D tables of commod- employment, and population as exogenous inputs. The ity flows to modal networks. The O-D table, produced by ap- regional economic and demographic module determines plying commodity trip generation and distribution steps to the total production activity in all the economic sectors the resulting employment O-D table, is split to freight modes other than the households sector over the entire model area based on existing shares or a diversion method. The modes each year. The production sectors in the model are listed in are two-axle truck, 3+-axle truck, rail, auto and van, water Table 8.51. and air cargo. Besides the production sectors, the Oregon Statewide Model has four sectors for final demand: exports, consump- tion, investment, and government (state and local). Table Markets 8.52 shows commodity categories included in the model. The model covers the State of Oregon and extends about 50 miles beyond the state boundaries to the south, east, and BASE AND FORECAST YEAR SOCIOECONOMIC DATA north. Each major mode has a separate network. The road network for goods and services matches MPO networks. The State DOT and MPOs maintain base year and the future freight rail network matches track alignments within Oregon. year forecast data. These data are used for travel demand

OCR for page 119
123 Table 8.51. Production sectors included in the Oregon model. Agriculture in Production in the Agricultural Industrial Sector that is located in Office Development Space Office Space and consumes Managerial, Professional and Clerical Labor Agriculture in Production in the Agricultural Industrial Sector that is located in Agricultural Development Agricultural Space Space and consumes Agricultural Labor Forest in Production in the Agricultural Industrial Sector that is located in Office Development Space Office Space and consumes Managerial, Professional and Clerical Labor Forest in Production in the Agricultural Industrial Sector that is located in Forest Development Space Forest Space and consumes Agricultural, Unskilled and Other Labor Light Industry in Production in the Light Industry Industrial Sector that is located in Office Development Space Office Space and consumes Managerial, Professional and Clerical Labor Light Industry in Light Production in the Light Industry Industrial Sector that is located in Light Industrial Development Industrial Space Space and consumes assembly and Fabrication, Semiskilled Manual and Other Labor Heavy Industry in Production in the Heavy Industry Industrial Sector that is located in Office Development Space Office Space and consumes Managerial, Professional and Clerical Labor Heavy Industry in Production in the Heavy Industry Industrial Sector that is located in Heavy Industrial Heavy Industrial Space Development Space and consumes Assembly and Fabrication, Semiskilled Manual and Other Labor Wholesale in Production in the Wholesale Industrial Sector that is located in Office Development Space and Office Space consumes Managerial, Professional and Clerical Labor Wholesale Industry in Production in the Warehouse Industrial Sector that is located in Warehouse Development Space Warehouse Space and consumes Semiskilled Manual, Unskilled Manual and Other Labor Retail in Production in the Retail Industrial Sector that is located in Office Development Space and con- Office Space sumes Managerial, Professional and Clerical Labor Retail in Production in the Retail Industrial Sector that is located in Retail Development Space and con- Retail Space sumes Retail and Other Labor Hotel and All production in the Hotel and Accommodation Sector that is located in Hotel Development Accommodation Space and consumes all categories of Labor Construction All production in the Construction Sector that is located at construction sites and consumes all categories of Labor Health Care in Production in the Health Care Industrial Sector that is located in Office Development Space and Office Space consumes Managerial, Professional, Clerical and Health Care Labor Health Care in Production in the Health Care Industrial Sector that is located in Hospital Development Space Hospital Space and consumes all categories of Labor Health Care in Production in the Health Care Industrial Sector that is located in Institutional Development Institutional Space Space and consumes all categories of Labor Transportation Handling Production in the Transportation Handling Industrial Sector that is located in Office in Office Space Development Space and consumes Managerial, Professional and Clerical Labor Transportation Handling Production in the Transportation Handling Industrial Sector that is located in Depot in Depot Space Development Space and consumes Semiskilled Manual, Unskilled Manual and Other Labor Other Services in Production in the Agricultural Industrial Sector that is located in Office Development Space Office Space and consumes Managerial, Professional and Clerical Labor Other Services in Light Production in the Other Services Industrial Sector that is located in Light Industrial Industrial Space Development Space and consumes Assembly and Fabrication, Semiskilled Manual, Unskilled Manual Labor and Other Labor Other Services in Production in the Other Services Industrial Sector that is located in Retail Development Space Retail Space and consumes Retail Labor Grade School Education in Production in the Grade School Education Industrial Sector that is located in Office Office Space Development Space and consumes Managerial, Professional and Clerical Labor Grade School Education in Production in the Grade School Education Industrial Sector that is located in Grade School Grade School Space Development Space and consumes Grade School Teaching Labor Post-Secondary Production in the Post-Secondary Education Sector that is located in Institutional Development Education Space and consumes all categories of Labor Government in Production in the Government Industrial Sector that is located in Office Development Space Office Space and consumes Managerial, Professional and Clerical Labor Government in Government Production in the Government Industrial Sector that is located in Government Support Support Space Development Space and consumes all categories of Labor Government in Production in the Government Industrial Sector that is located in Institutional Development Institutional Space Space and consumes all categories of Labor Source: J.D. Hunt and others, Design of a Statewide Land Use Transportation Interaction Model for Oregon, 2001.

OCR for page 119
124 Table 8.52. Commodity categories included in the Oregon Statewide Model. Farm Products Forest Products Fresh Fish or Marine Products Metallic Ores Coal Crude Petroleum, Natural Gas or Gasoline Nonmetallic Minerals Ordnance or Accessories Food or Kindred Products Tobacco Products, Excluding Insecticides Textile Mill Products Apparel or Other Finished Textile Products or Knit Apparel Lumber or Wood Products, Excluding Furniture Furniture or Fixtures Pulp, Paper or Allied Products Printed Matter Chemical or Allied Products Petroleum or Coal Products Rubber or Miscellaneous Plastic Products Leather or Leather Products Clay, Concrete, Glass or Stone Products Primary Metal Products, Including Galvanized Fabricated Metal Products Machinery, Excluding Electrical Electrical Machinery, Equipment or Supplies Transportation Equipment Instruments, Photographic Goods, Optical Goods, Miscellaneous Products or Manufacturing Watches or Clocks Waste or Scrap Materials Not Identified by Other (Miscellaneous) Freight Shipments Producing Industry Containers, Carriers or Devices, Shipping, Waste Hazardous Materials or Waste Hazardous Returned Empty Substances Construction Services Pipeline Transportation Services Transportation and Storage Services Radio and Television Broadcasting Services Postal Services Utilities Services Wholesale Margins Retail Margins Other Finance, Insurance and Real Estate Services Business Services Education Services Health Services Amusement and Recreation Services Accommodation Services Food Services Other Personal and Miscellaneous Services Managerial Labor Professional Labor Grade-school Teaching Labor Clerical Labor Assembly and Fabrication Labor Agricultural Labor Semi-skilled Manual Labor Unskilled Manual Labor Retail Labor Health Care Labor Post-secondary Teaching Labor Other Labor modeling, land use allocation models, and policy analysis as Portland to Seattle and Spokane. Goods from California also required under Federal guides and the statewide planning make up a large share of inbound shipments. Together, program. These databases are forecasts that support statewide Washington and California account for over three-quarters planning for interstate freight and passenger movements and of all inbound truck shipments to Oregon. distribution of population and employment growth. Modal Networks EXTERNAL MARKETS FREIGHT MODAL NETWORKS Goods from Washington State make up the largest in- The model covers the State of Oregon and extends about bound shipments, reflecting the geographic proximity of 50 miles beyond the state boundaries to the south, east, and

OCR for page 119
125 north. This coverage area is made up of internal zones. Other provides productions in each economic sector, imports and regions of the United States are considered external zones. exports by economic sector, employment by labor category, The internal zones are the locations of production, con- and in-migration and payroll by sector for each year. sumption, and exchange. They are largely based on Census tracts and are nested into counties. The internal zones inside Oregon contain grid cells, while the internal zones outside Conversion Data Oregon do not. Zones are consistent with MPO internal zones. The model estimates yearly flow of commodities among With about 3,000 zones spread across the state, the model TAZs, which it converts to daily weekday freight movements. uses finer spatial disaggregation than most integrated land The commercial movement module is used to determine the use-transportation models. Internal zones are further divided growth of truck movements during a particular workday in into grid cells and link tributary areas. Grid cells are the small- each year. It synthesizes a fully disaggregated list of individ- est units, and they nest completely into both of the other two. ual truck movements. Shipment sizes are chosen to be con- A grid cell is a square of land small enough to include a sin- sistent with the CFS. gle type of developed space (one category of building floor space). Cells are typically 30m 30m in and near built up areas and 300m 300m or even larger in less densely popu- Validation Data lated spaces. A total of about 14.5 million grid cells cover the entire model area. The entire model was run and then compared with the The zones are connected to the transportation network weighted observed data to obtain a goodness-of-fit measure. using centroid connectors, as in a conventional travel fore- casting model. Link tributary areas are grid cells that feed a Model Development particular link and are contained within a single zone. It is possible for a single link to have more than one tributary area The activity location and transportation network interface if it is located on or near the boundary of more than one zone. produces the trip O-D matrices of demands and possible Different parts of the model use different systems of spatial exogenous trips. The transportation model transforms these aggregations, depending upon the needs for spatial precision. demands into actual trips and assigns them to the networks Units of time vary throughout the model. Land use allocation systematically. and economic activity are stepped over time in one-year The first step in the modeling process is to find all possi- increments. Thus, activity allocation will tend toward equi- ble paths, after which the process starts an iterative cycle. librium but is not in equilibrium in any given year. Both money and generalized costs along each path are calcu- Each major mode has a separate network. The road net- lated initially. A weighted arithmetic average cost over all work (for goods and services) matches MPO networks within paths is calculated for monetary costs, but composite costs urban areas and is similarly detailed in rural areas. The freight are aggregated from a path level to a mode level through a rail network matches track alignments within Oregon. Exter- logarithmic average. Similarly, aggregated costs over all nal areas in both networks are shown skeletally, becoming modes are estimated to obtain the average monetary and sparser as the distance from Oregon increases. composite cost of travel from an origin to a destination for a The model is dynamic in two distinct ways: 1) it calculates given user category. changes in activities over time (years), and 2) traffic is The next two steps in the modeling process are trip gener- assigned microscopically by time period. The activity alloca- ation and trip distribution. Trip generation transforms the tion aspects of the model give a disequilibrium treatment of potential travel demand into actual trips. It estimates the land markets and activity allocations while allowing an equi- number of trips from an origin to a destination by a particu- librium treatment of transportation and commodity markets. lar transport category, which is a function of the correspon- The regional economic structure and land use are done using ding composite cost. relations similar to those in TRANUS (used in TLUMIP1), an Trips for each category are split to modes by means of a aggregate integrated land use-transport model. Oregon's Multinomial Nested Logit (MNL) model in which the utility model is intentionally strong in statewide freight forecasting function is determined by the composite cost of travel by so that it can reliably evaluate the effects of economic policy mode. Mode choice is made over all modes available to each changes and future population and economic growth. category. Trips by mode assigned to the different paths con- nect origins and destinations by that mode. Since each path implies a particular sequence of operators and transfers, trips Model Development Data are simultaneously assigned to operators, as well as to links of The model consists of seven modules, one of which ad- the network. There is an option in the model to check the dresses regional economics and demographics. This module empty returning vehicles.

OCR for page 119
126 Software equivalent to the two-level hierarchical modal split model. Both models are nested through composite costs. The Oregon Statewide Model has it roots in TRANUS, an integrated land use and transportation model that can be applied at an urban or regional scale.28 TRANUS has two pur- Trip Distribution poses: 1) to simulate the probable effects of applying partic- The goods and services shipments flows are determined as ular land use and transport policies and projects, and 2) to part of the spatial distributions of activities and population, evaluate these effects from social, economic, financial, and following the path from the production locations to the energy points of view. exchange locations and then to the consumption locations. TRANUS has two main components: land use and trans- There is no separate trip distribution step like the four-step portation. The relation between the two over time is shown modeling procedure. in Figure 8.26. Because land use and transportation influence one another, a change in the transportation system, such as a new road, a mass transit system or change in rate charges, will Commodity Trip Table have an immediate effect on travel demand. Not applicable. Commodity tables were not used directly but were used to support the development of model parameters. Trip Generation The TRANUS model converts demand into actual trips Mode Split and assigns them to various supply options of routes. The Mode split and assignment are accomplished together as a sequence of the model is shown in Figure 8.27. First, it gener- simultaneous loading to a multimodal network. The multi- ates a set of paths connecting origin and destination of trips mode network represents the supply of various combinations by each transport mode (freight, private auto, public trans- of available goods and services transportation. The mode port, etc.). Again, freight might be subdivided into light, alternatives are: two-axle truck, 3+-axle truck, rail, auto and medium, and heavy trucks. van, water, and air cargo. Second, TRANUS transforms the potential travel demand Utility is the measure of spatial separation throughout the calculated by the activity/transport interface into actual trips Oregon Model. Utility separates persons from their activity at particular time of the day (peak, off-peak, 24 hours, etc.). sites, separates points of production from points of consump- Trips for each category are distributed to modes by means of tion, and separates vehicles from their origins and destinations. a MNL logit model in which the utility function is determined Utility is part of several choice processes with many alterna- by the composite cost of travel by mode. Next, a mode is cho- tives, such as modes or locations. Thus, in general: sen from among the modes available to each category. Third, TRANUS assigns trips by mode to the different Ui, a = f (ai, Xa) paths connecting origins to destinations by that mode. Trips where are simultaneously assigned to operators and to links of the i = index representing individuals, network. This also is carried out by a MNL model. The com- a = index representing alternatives, bination of the MNL model split and assignment models is Ui, a = utility determined for alternative a for individual i, Time T1 Time T2 Time T3 Land Use Land Use Land Use Transport Transport Transport Source: Modelistica Systems and Planning, Caracas, Venezuela. Figure 8.26. Dynamic relations in the land use-transport system.

OCR for page 119
127 Parameters Read/Verify Inputs Path Search by Mode Network Cost and Disutilities Potential Travel Demand Trip Generation Generation Functions Captivity Modal Split Empty Returns Consolidation Parameter Assignment of Trips Changes in Speeds and Capacity Restriction Functions Waiting Times No Convergence Criterion Coverage? Link Loads by Operation Output Results Trip Matrices Travel Costs Yes New Set of Path? End Source: Modelistica Systems and Planning, Caracas, Venezuela. Figure 8.27. Calculation sequence of the transport model. ai = vector of utility function coefficients indicating sen- part by the conditions determined for year t. These yearly sitivities of individual i to attributes of alternative, freight movements then are converted to a representative and weekday. Xa = vector of attribute values for alternative a. The model has six manifestations of utility described in Assignment Table 8.53. The transportation supply module is a hybrid of macro- scopic and microscopic techniques. A standard equilibrium Flow Unit and Time Period Conversion assignment is made using congested travel times and the The commercial movement module is used to determine resulting origin to destination travel times also are saved. the growth of freight movements during a representative These equilibrium travel times are then used in a microscopic workday in each year. In fact, the model steps through time assignment, which works at the level of individual vehicles, in a series of one-year steps that allow the entire system to determining the network loadings from synthesized demands evolve. The representation for year t + 1 is influenced in of the household travel and commercial movements.

OCR for page 119
128 Table 8.53. Utility definitions in the Oregon Statewide Model. Utility Format Attribute Value Xa Sensitivity Values ai Rutlity Allocations of aggregate Average, zonal, or typical. Typical values for the category (Representative) quantities. of aggregate quantity being allocated. Zutility Agent-based microsimulations of Average, zonal, or typical. Specific values assigned to the (Zonal) individual household and person household or person. decisions. Iutility Network path selection for Specific link values. Aggregate values assigned to (Interchange) aggregate, zone-to-zone trip flow the flow being assigned. assignment. Lutility Network path selection for Specific link values. Typical values assigned to the (Link) individual trip. trip-making agent. Cutility Microsimulations of land Specific grid cell values. Typical values assigned to the (Cell) development decisions. developers as a single category. Model Validation observed volume. Some targets are more important than others. Model calibration establishes mathematical equations that First, submodels and individual relationships within the var- replicate observed behavior. Model validation is the process ious modules were calibrated separately from the overall mod- of comparing model outputs against data to determine how eling system and then the entire model was calibrated. The well the model simulates aggregate measurements of behav- entire model was run and then compared with the weighted ior. Although the model has not yet been fully validated, the observed data to obtain a goodness-of-fit measure. Certain following data are going to be used for the validation of the parameters were adjusted and the model was rerun to deter- model. mine the effect of the adjustments. Finally, during the applica- tion of the model, the long-range results of the alternatives were IMPLAN29 survey; evaluated to ensure that reasonable results were being obtained. Oregon household travel survey; State employment records; Highway and local road inventories; Trip Generation County assessment records; The second generation Oregon Statewide model has not Land sales records; been validated. The trip generation step is also not validated. Metro (Regional Inventory System) data; Statewide zoning; and U.S. Census Bureau data. Trip Distribution Validation data for trip generation step are not available in The study team and peer review panel together developed the Oregon Statewide model documentation. several criteria for assessing model performance: Match production by sector and zone; Mode Choice Match number of trips and average trip distances by trip Validation data for mode choice step are not available in purpose; the Oregon Statewide model documentation. Minimize zone-specific constants by sector; Network flows to match counts by mode of transportation, Modal Assignment with emphasis on inter-urban routes; Match increments of land to changes in land price; and Submodels and individual relationships within the various Match Central Transportation Planning Package distribu- modules are calibrated first, separate from the overall model- tion for commuting flows. ing system, and then the entire model is calibrated. The calibrator facilitates the calibration of the entire model by Each criterion has it own target number. The network vol- running the model and comparing its outputs with a selec- ume must be within plus or minus a certain percentage of the tion of weighted observed data to provide a goodness-of-fit

OCR for page 119
129 measure. However, the validation statistics are not available demographic, passenger, and commodity flow forecasts at the in the documentation. statewide and substate levels. Model Application Performance Measures and Evaluation As of this writing, the second generation Oregon model has Performance measures were not developed for the Oregon not been applied for any projects. However, the model will be model. However, the model outputs can be used in other used to analyze and support land use and transportation analysis packages for assessing transportation system per- decision-making; and to make periodic, long-term economic, formance.