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The Travel Model Improvement Program Newsletter

Issue 3, July 1995

The Travel Model Improvement Program is sponsored by:
U.S. Department of Transportation
Federal Highway Administration
Federal Transit Administration

Table of Contents
TMIP Launches Data Research Initiative Under Track D
Land Use Modeling Conference
Upcoming Conferences Related to TMIP
Conference on the Role of Metropolitan Planning Organizations in Transportation Planning
TMIP News
Listing of Available Reports
TRAMSIMS Travelogue

TMIP Launches Data Research Initiative Under Track D

A long-term research program was initiated recently focusing on improving transportation data collection, analysis and use. Two major areas of research are being targeted: improving data collection methods to support States and MPOs to better respond to ISTEA and CAAA '90; and data needs for travel model improvement and development efforts. A framework for a multi-year program has been developed and several quick-start projects are due for completion later this summer. These projects will feed into a white paper addressing:

  1. current data collection practices and capabilities of States and MPOs to support travel modeling,
  2. near and long-term trends in data collection practice,
  3. gaps between current practice and state-of-the-art,
  4. data needs to support contemporary and emerging model systems,
  5. emerging technologies for data collection,
  6. recommendations for research over the long term, and
  7. proposals for filling in the details of the Track D research program.

Additional detail and other Track D projects are covered on page 7.

Table of Contents

Land Use Modeling Conference

The Travel Model Improvement Program (TMIP) sponsored the Land Use Modeling Conference February 19-21, 1995, in Dallas, Texas. Eighty members of the land use, environmental, and transportation planning, consulting and academic communities participated in the conference. The conference program was designed to stimulate discussion on the current land use modeling needs and issues with the overall objective of establishing an agenda for land use modeling research to support the TMIP.

Improvements to existing travel models and the new generation of models being developed will require more sophisticated land use forecasts. Simply estimating the number of employees or residents in a zone is not adequate for activity based travel models, which require detailed information and precise locations on household demographics and employment characteristics. Many policy initiatives require detailed and sophisticated land use/activity forecasts as well.

The conference brought together experts and practitioners to identify:

The first day of the conference examined how well existing land use modeling and forecasting methods address the current issues and mandates, the advantages and disadvantages of existing models, and how they may be improved to address the current needs. The second day centered on discussions of new land use modeling and forecasting techniques. Approaches and techniques that have recently been developed but need to be implemented and others that are still conceptual were discussed. Additionally, issues surrounding data requirements, model architecture and the model development process were examined.

Six conference workshop groups each developed recommendations for research, development and implementation of land use models and forecasting techniques. For the short term there was a broad consensus that there is a need for a comparative description of the theory, variables and parameters of currently available models that would allow agencies to make informed choices for model applications. A need for guidelines and advice on the process in which the models are used was also cited by the workshop participants. Pilot programs to implement a range of land use forecasting techniques from which experience and guidance could be developed were recommended.

Extensive research needs to improve the precision, accuracy and usefulness of the model output were identified. Participants indicated that the models need to address a wider range of policies and their impacts, account for environmental constraints, and consider the actions of individuals, governments, developers, businesses and investors. There should not be an attempt to develop a single model to accomplish all tasks. Rather, any new model system should be modular, each piece having a specific purpose, to allow for intervention to adjust data and information and to accommodate varying levels of spatial resolution as well as temporal dynamics. New models should be fully compatible with geographic information systems (GIS) and should be capable of linking with transportation and environmental models.

The need for research on data collection/acquisition strategies, employment data, and the generation and use of synthetic data was recognized by all six workshops. Additional research on individual and business location choice decision processes and the use of stated preference and revealed preference surveys were also identified by the participants.

The conference was a success, and the TMIP support staff are using the results to develop a research agenda for land use modeling and forecasting needs to support the transportation and environmental models being developed in the TMIP. Proceedings of the conference are expected to be available in August 1995.

Table of Contents

Upcoming Conferences Related to TMIP

Table of Contents

Conference on the Role of Metropolitan Planning Organizations in Transportation Planning, Williamsburg VA, May 21-24, 1995

A recent TRB conference, Institutional Aspects of Metropolitan Transportation Planning focused on improving the ability of MPOs to respond to national transportation policies such as ISTEA. A background report for the conference, "MPO CAPACITY: Improving the Capacity of Metropolitan Planning Organizations to Help Implement National Transportation Policies," was prepared by the U.S. Advisory Commission on Intergovernmental Relations (ACIR) under a FHWA contract. Surveys of 18 MPOs from across the country resulted in six major recommendations including the following which is particularly relevant to TMIP.

Recommendation

The U.S. DOT should establish a more comprehensive capacity-building program for MPOs that:

  1. addresses the needs of all participants in the MPO process,
  2. makes affordable and effective assistance available to all MPOs,
  3. covers a broad array of topics, and
  4. provides a broad array of services.

Both the conference and the paper emphasized the needs for expanded cooperation between the MPOs, state DOTs, and U.S. DOT to achieve the goals of ISTEA and other policies. Break-out sessions at the conference focused on specific needs and concerns and developed both long-term and short-term recommendations. Those recommendations will be incorporated in future TMIP activity. To obtain a copy of the MPO CAPACITY report, please call ACIR at (202)653-5540. The conference proceedings will be available from the TRB in 1996.

Table of Contents

TMIP News

Track A

The definition and work on Track A have progressed considerably since January. The Texas Transportation Institute staff are focused on four areas of outreach and technical assistance: a travel modeling clearinghouse, a pilot technical assistance center, a bulletin board, and an Internet home page.

Clearinghouse

A collection of references, abstracts, and full text documents will be compiled to simplify the search for existing research. Initially the clearinghouse will focus on transportation modeling, but in the future the collection will be broadened to include other transportation planning and related topics. This collection will go beyond the service currently offered by TRIS and others in several ways. First an effort is underway to scan older documents and to obtain electronic versions of as many relevant new reports as possible. This will provide users with immediate access to documents of interest. Second a systematic effort is now underway to contact transportation and planning organizations to locate reports, papers, and projects which would be of interest to others. Finally, through the efforts of FHWA, electronic versions of the work programs undertaken by local agencies will be obtained. This will help identify for contact those local agencies conducting studies of national interest.

This clearinghouse will provide access to the widest audience possible. It will be available on the bulletin board and the Internet home page described below, and TTI staff will search the database and provide hard copy for those without modem or Internet access.

Bulletin Board and Internet

A transportation modeling bulletin board will be established. Initially the bulletin board will include the clearinghouse references and a location to post and answer modeling questions. Topic folders, keyword searching capability and other techniques will be used to ease the task of finding relevant information, and a systems administrator will be available to help users when necessary. The home page will be developed in cooperation with Bureau of Transportation Statistics. The clearinghouse will be accessible through the BTS home page. Eventually the home page will include information on training and conferences, transportation and planning organizations, and an opportunity for interaction between modeling professionals. Both the bulletin board and the home page will be operational shortly.

Regional Technical Assistance Centers

A pilot technical training and assistance center is being established in Texas. That center will provide telephone or hands-on assistance to transportation planners in a limited area. The center will be staffed by persons with working technical experience in travel models and other transportation planning techniques. The center will also provide on-call assistance from subject area experts as the needs require. Depending on the experience with this pilot, centers in other areas may be established.

Track B

Track B projects are organized in three general areas: manuals of practice, new capabilities, and analysis of modeling issues. Availability of reports on projects currently underway will be announced in future newsletters. More information on these projects is available from Kim Fisher at (202)366-4054.

Manuals of Practice

Manual of Basic Travel Demand Procedures

This new manual is designed to be an introductory text and reference for persons who will be using travel demand forecasting models and model results. This will be the first new travel forecasting primer distributed by the U.S. DOT since 1977. Work is beginning on this project, and the manual will be available from U.S. DOT early in 1996.

Telecommuting Impact Analysis Manual

This project will identify the various telecommuting options from home and other locations; develop techniques for forecasting the use of telecommuting and potential impacts of telecommuting options; and safety impacts of region-wide telecommuting programs. It is anticipated that work on this project will start in the summer of 1995 and the manual will be available from U.S. DOT in the spring of 1996.

Validation Manual

This manual will describe procedures that can be used to perform validation and reasonability tests of travel demand models. These tests apply to both highway and transit demand. The emphasis is on comparing actual to simulated demand to determine if the travel demand model results are within an acceptable level of accuracy. The project began in May of 1995 and will be completed in the fall of 1995.

Freight Forecasting Manual

This will be a quick response manual for freight modeling and planning for state departments of transportation and MPOs. The manual will describe the range of actions that affect the efficiency of the freight system and their impacts, identify the information needed to evaluate these actions, and provide a practical technique for developing a freight model. The project is underway and expected to be complete in the spring of 1996.

Congestion Pricing Manual

This manual will provide background information on congestion pricing including definition, issues, and state- of-the-art. A literature review will be conducted. The manual will also describe how to develop and evaluate congestion pricing projects. The project has not been awarded.

Transit Access Network Coding Guide

The objective of this guide is to document the best methods used in travel demand forecasting procedures to represent how local conditions and land features influence access to transit. The strengths and weaknesses of each method will be described. The inter-relationships between the access representation methods, transit pathbuilding procedures and mode choice models will be documented. The product of this work will describe the best practices for transit access representation and procedures for implementing those methods. Work began on the manual in May 1995, and should be completed in the spring of 1996.

New Capabilities

Activity Based Travel Demand Forecasting

The potential of performing travel forecasting based on generation of activities rather than trips is being tested in this project. A stated preference survey collected data on travel chains related to commute trips and responses to transportation demand management strategies. The model will be able to predict commute mode shift, changes in departure time and changes in trips made as part of the home-to-work or work-to-home trip chain. The survey has been conducted, results were summarized and work continues on the model. Results are expected in the winter of 1995.

Multi-Criteria Traffic Assignment

This software performs an equilibrium traffic assignment using time and cost as criteria. This will allow assignments for travelers with different values of time so that the impact of policies such as congestion pricing can be assessed, recognizing that users will respond according to their individual values of time. The software is being designed for implementation within TRANSCAD but with capability for incorporation into other modeling packages. The algorithm is currently being tested using networks and traffic data from Boston in cooperation with the Central Transportation Planning Staff. This test is expected to be complete in the winter of 1995.

Identification of Short Term Travel Model Improvements

This document identifies potential short term improvements to the existing urban travel models. This was accomplished by first documenting the most innovative techniques being used today, and then identifying promising techniques which have not yet been put into practice. An overview report titled "Short Term Model Improvements" was completed in August, 1994, and is now available from the Technology Sharing Program of the U.S. DOT (Report #DOT-T-95-05). This report highlights innovative applications and possible research. More detailed descriptions of each of the major innovative model applications in this report will be produced so that practitioners can better understand exemplary techniques being used around the country. Currently detailed descriptions are being written for four modeling areas: time-of-day assignment, non-vehicular travel, auto ownership, and speed post-processing. These will be followed by descriptions of other techniques yet to be determined. The detailed reports on the four areas listed will be available in the fall of 1995.

Analysis of Modeling Issues

Identification of Transportation Planning Data Requirements in Federal Legislation

This report identifies the new planning and associated data collection requirements set forth in the Clean Air Act Amendments (CAAA) of 1990 and the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991. This report also identifies the shortcomings of the existing set of transportation planning models in terms of their ability to fulfill the new requirements. The report is complete and available through the Technology Sharing Program of the U.S. Department of Transportation, Report Number DOT-T-94-21.

Effects of Land Use and TDM Strategies on Commuting Behavior

This report presents the analytical results of a larger project undertaken for the Federal Highway Administration, investigating the "Effects of Land Use and Demand Management on Traffic Congestion and Transportation Efficiency." The work reported represents an ambitious program of data collection and analysis of employment sites located in Los Angeles metropolitan area.

Activities were carefully designed so that the most appropriate land use and urban design variables could be tested to determine their influence on travel behavior. The report is complete and available through the Technology Sharing Program of the U.S. Department of Transportation. Report Number DOT-T-94-21.

Equilibrium Issues in Land Use and Transportation

This project is an investigation of the impact of feeding back congested travel times from traffic assignment to the land use forecasting process. A number of different cities with various levels of traffic congestion will be tested to gain an understanding of the conditions in which feedback should be applied. The project will address the conditions under which feedback between land use and transportation makes a difference in travel forecasts, how much of a difference it makes, and technical issues in implementing feedback loops. Preliminary results are available from U.S. DOT for Portland and Los Angeles, and further tests are planned for other areas. Final results will be available in the winter of 1995.

Travel Time Feedback into Distribution

This project is an investigation of equilibrium issues between trip distribution, mode choice, and traffic assignment. Databases from two cities have been obtained, and a feedback loop from assignment to distribution has been created. Issues to be addressed include convergence between iterations of the feedback loop and conditions under which feedback makes a difference in the final forecast. The report will be available early in the 1996.

Investigation of Transit Transfer Penalties

This project is being conducted to determine the appropriate magnitude of transfer penalty above that incurred by waiting for the vehicle. Stated preference work to date, both in the U. S. and abroad, indicates that penalties of up to 30 minutes of in-vehicle time could be incurred by transferring, but estimation of mode share models rarely, if ever, show a penalty. By paying particular attention to network impedances and mode share estimation, this study is intended to find if a penalty exists for the Boston area, and make recommendations for other areas. A number of mode share estimations with a variety of assumptions have been run. Preliminary results show coefficients are more significant with manually coded impedances and mode generic in-vehicle coefficients. A penalty of as much as 15 minutes has been observed. The final report for this project will be available in the fall of 1995.

Track D

Travel Survey Manual

This manual will provide the latest information on several kinds of surveys: household, transit on-board, vehicle intercept, commercial vehicle/freight, workplace/ establishment/visitor, panel, stated preference, special generator and parking. For each of these survey types, the information will include, conduct of the survey, administration, design, sampling, data collection procedures, pre-testing and data entry, verification and analysis. In addition survey forms, contacts and example requests for proposals will be included. A draft report has been completed and reviewed by TMIP staff. Review by staff outside the Department will begin in the summer of 1995. The manual will be published in early 1996. A course is also being developed based on this manual.

Quick Start Projects

A report will be prepared assessing the state-of- the-practice versus the state-of-the-art in travel data collection. This work will summarize the results of several investigative activities by the contractor, including a scan of recent and current research and a synthesis of previous conference recommendations and other "off-the-shelf" research statements. The information will be used as a basis for recommending a long-range research program for Track D. Work on this report is currently underway and should be complete in the fall of 1995. The results will be reported in a summary report and an issue paper.

Data Collection Case Study

A case study of Portland Oregon will be prepared to illustrate the application of leading edge, state-of- the-practice data collection. This case study will describe recent and planned comprehensive transportation data collection in the metropolitan area. The data covered will be for both motorized and non-motorized travel modes as well as for the full spectrum of the travel demand modeling process, from socio-economic and land use data through traffic volumes, speed, and vehicle classification.

Data Note Number 1

There are now two different ways to reach the Census BBS.

Data Note Number 2

An instructional guide for using the 1990 Census Transportation Planning Package (CTPP) is now available. "THE CTPP HANDBOOK: An Instructional Guide to the 1990 Census Transportation Planning Package" gives users an overview of the CTPP and includes discussions of basic Census definitions and CTPP organization tables and parts. Self instructional case studies included make use of simple spreadsheets and provide hands-on experience with concepts and potential uses of CTPP data. The report may be obtained by faxing a request to (202)366-2795 or by writing to: Property Use and Storage Section , M45.3 Room 2200, 400 Seventh Street, SW, Washington D.C. 20590. When requesting the document, you must note both the title, the CTPP Handbook: An Instructional Guide to the 1990 Census Transportation Planning Package, and the publication number, FHWA-PD-95-019.

Track E

Descriptions of Land Use Models

This report will describe land use models in use today both in and outside of the United States. In the Land Use Modeling Conference described earlier in this newsletter, participants identified a need for information on land use models being used in other countries. While a few reports have documented those modeling capabilities, a need to expand on previous work was identified in order for practitioners to better understand model options. Work began in June 1995 and is expected to be complete by September 1995.

Table of Contents

Listing of Available Reports

Addresses for report contacts:

Kim Fisher
c/o Federal Highway Administration
400 7th St SW, HEP-22, Room 3232
Washington, DC 20590
Phone: (202) 366-4054, Fax: (202) 366-3713

Lynette Engelke
Texas Transportation Institute
201 E. Abram Street, Suite 600
Arlington, TX 76010
Phone: (817) 277-5503, Fax: (817) 277-5439

Norman Paulhus
Technology Sharing Program
U.S. DOT
400 7th Street, SW, M-453
Washington, D.C. 20590

Table of Contents

TRANSIMS Travelogue — June 1995

What is TRANSIMS?

The TRansportation ANalysis and SIMulation System (TRANSIMS) is one part of the multi-track Travel Model Improvement Program sponsored by the U.S. Department of Transportation, the Environmental Protection Agency, and the Department of Energy. The TRANSIMS project has been identified as a major effort to develop new, integrated transportation and air quality forecasting procedures necessary to satisfy the Intermodal Surface Transportation Efficiency Act and the Clean Air Act and its amendments. TRANSIMS is a set of integrated analytical and simulation models and supporting data bases whose development is led by the Los Alamos National Laboratory. The TRANSIMS methods deal with individual behavioral units and proceed through several steps to estimate travel. TRANSIMS predicts trips for individual households, residents and vehicles rather than for zonal aggregations of households. TRANSIMS also predicts the movement of individual loads of freight. A regional microsimulation executes the generated trips on the transportation network to predict the performance of individual vehicles and the transportation system. Motor vehicle emissions are estimated using traffic information produced by TRANSIMS. A major advantage of TRANSIMS for air quality analysis is the detail it provides regarding motor vehicle operation. Our approach is to develop an interim operational capability (IOC) for each major TRANSIMS component. When the IOC is ready, we will complete a specific case study to confirm the IOC features, applicability, and readiness. We will complete the specific case study with the collaboration of a selected MPO staff. This approach should provide timely interaction and feedback from the TRANSIMS user community and more interim products, capabilities, and applications.

The Traffic Microsimulation will be the first IOC, with the goal of having it ready for testing near the end of calendar year 1995. As this IOC is developed, we will work with the selected MPO, North Central Texas Council of Governments (NCTCOG) (Dallas-Fort Worth), to identify studies that the IOC should support.

TRANSIMS Architecture

Before we began development specific to the Traffic Microsimulation Interim Operational Capability (IOC), we established the overall TRANSIMS software framework and architecture. This comprehensive planning and design effort has required time and effort, but should result in a flexible, robust structure for research and development of future TRANSIMS capabilities. The methods for the later IOCs should be implemented more quickly within this architecture without significant design changes. To provide computational speed and an operational capability available to end users in the near term, we are developing the first IOC to be distributed for parallel computation on a network of SUN workstations.

We established an architecture design team to develop the architectural framework for the TRANSIMS software. The architecture goal was to ensure that the various TRANSIMS components are integrated effectively, for the first IOC, future IOCs, and the final TRANSIMS software. The architecture is designed so that TRANSIMS is flexible, expandable, portable, and maintainable throughout its lifetime.

The resulting framework, shown in Figure 1, is a layered architecture with the following layers:

Application: The Analyst Toolbox, which provides a centralized interface between the user and TRANSIMS.

System: Interim Household and Commercial Activity Disaggregation, Interim Intermodal Route Planner, Low Fidelity, Microsimulation, Input Editor, and Output Visualizer centralize access to the major functional components of TRANSIMS. Additional systems will be added for future IOCs and the end product will be added for future IOCs and the end product.

Subsystem (High-Level): Ten subsystems have been identified that provide services to one or more of the TRANSIMS systems. The subsystems enhance the reusability and flexibility of the software.

Subsystem (Low-Level): Six representational subsystems provide basic services (data and operations on data) to the high-level subsystems. They provide a common representation of objects such as vehicles, travelers, the transportation network, etc.

Subsystem (Utility): The utility subsystems provide basic domain-independent services to the higher level components of TRANSIMS. They isolate the domain subsystems from dependence on operating systems, file systems, etc.

TRANSIMS Software Architecture for the Traffic Microsimulation Interim Operational Capability

Figure 1 – TRANSIMS Software Architecture for the Traffic Microsimulation Interim Operational Capability

The architectural design team prepared recommendations for the software and hardware development environment for TRANSIMS. We selected several commercial products to leverage our development activities. We established the software engineering process to be followed, including coding and documentation standards, configuration management, iterative object-oriented development, and procedures for review and testing. After the formal review and acceptance of the recommendations, we started implementing the recommendations by purchasing required software and hardware, establishing configuration management procedures, and instituting a software review process.

We initiated subsystem design of the TRANSIMS architecture by formation of design teams. The database subsystem team designed the database subsystem, a unified means of organizing, storing, and retrieving TRANSIMS data. Design teams have developed designs for the network representation, the traveler representation, establishment representation, plan representation, and vehicle representation. For example, the network representation subsystem provides a common representation of traffic networks and sub-networks consisting of nodes, links, lanes, and traffic control objects such as unsignalized controls and timed and actuated signals. Allowed movements, turn protections, and interfering lanes during turns can be computed from information in the basic network representation.

The Parallel Toolbox subsystem, developed initially by the TRANSIMS research team, distributes the microsimulation on a local area network of workstations for IOC-1. The research and microsimulation team members have been augmenting the Parallel Toolbox to interface the microsimulation with the network representation adopted for TRANSIMS.

Trip Plans for IOC-1

The first IOC traffic microsimulation will require trip plans (origins, destinations, departure times, routes, etc.) for the individual travelers. Because we are in the process of developing the methods to translate activity demand into transportation demand, the initial modules for the Household and Commercial Activity Demand and the Intermodal Route Planner will rely on existing data and extensions to current methods. These interim modules, their interfaces, and data flow will require few or no changes when the activity demand models become available. They also might serve a useful purpose for certain classes of analyses even after the activity-based methods become available for TRANSIMS. Techniques for creating baseline synthetic populations are described briefly in the next section.

The interim modules will take information regarding trip purposes within current origin-destination matrices or production-attraction tables and will assign up to three activities to each traveler. Additional information will identify activity destinations and generate simple travel goals and preferences. This interim planner will use simple cost functions, such as time or distance minimization, within the Likely Path algorithm to find the travelers' routes on current or expanded roadway networks. A trip plan incorporating origin; departure time; node, link, and expected arrival time sequence; and destination will be the output from the planner. For analyses within subregions of the metropolitan region, the plans will be truncated to apply only to the subregion.

Baseline Synthetic Populations

We have developed a procedure for creating a baseline synthetic population of households. The individuals in the households are used as travelers in the activity-based TRANSIMS model. This population is created from 1990 census data and is aged to the desired date. At this time we consider only the creation of the baseline population without "aging." These methods are described more completely in the document, "Creating Baseline Synthetic Populations," by Richard J. Beckman, Keith A. Baggerly, and Michael D. McKay.

The 1990 census data used to develop the baseline population includes the Census Standard Tape File 3 (STF-3) and the Public Use Microdata Sample (PUMS). We create distinct households for each census tract or block group area (we currently use census tracts). The procedure involves four stages. First, for the census tract in question, we group the census summary tables from STF-3 and the corresponding PUMS sample by family and non-family households. Second, for each household type, we construct a multiway table of the demographics available from STF-3. Third, we create households by random selection (according to the probabilities in the constructed multiway table) of similar households in the PUMS sample. The last stage consists of aging the population to the desired date.

The demographic summary tables in STF-3 for family households are (1) race of householder by household class (a combination of household type and presence and age of children), (2) age of householder, (3) family income, and (4) the number of workers in the family. We use these four summary tables and the corresponding sample from the PUMS to create the five-dimensional multiway table of probabilities for each combination of the five demographic variables. We use iterative proportional fitting to generate the multiway tables. It is easy to implement and it converges in a few iterations.

Synthetic Population Validation

We examined methods to validate and verify these household construction procedures. STF-3 contains a summary table for the total number of persons in family households. Because the total number of people is not controlled in the construction of family households, this summary can be used as one validation of the resulting population. We generated populations of households for census tract 1.07 of Bernalillo County NM. The resulting distribution of persons per household compares favorably with the "true" distribution given in STF-3A for that census tract.

For validation and verification of household characteristics not in STF-3 (for example, the number of vehicles by the number of people in the households), we can construct a synthetic collection of "census tracts" and corresponding synthetic "PUMS" samples. This relatively simple construction is accomplished by considering PUMS samples as complete "census tracts" and combining approximately 20 neighboring PUMS samples. The resulting population of approximately 100,000 people then is sampled to create the synthetic "PUMS" for the constructed "census tracts."

We created synthetic "PUMS" samples by combining 22 PUMS from the San Francisco Bay area. Using the 22 PUMS as complete "census tracts", we used the household generation procedure to create synthetic family household populations. The joint distribution of persons by household by the number of vehicles compared favorably with that known from the 22 PUMS. The resulting distributions fit the truth very well except for four City-of-San-Francisco PUMS where we overestimated the number of vehicles in households with few people. This is not unexpected because parking problems and a good mass transit system make owning multiple vehicles undesirable in the City. Hence, the correlation structure in the individual PUMS taken as "census tracts" differs from "census tract" to "census tract." In actual applications of the method on real census tracts or block groups, the census tracts in a PUMS will be more homogeneous than the PUMS used as "census tracts" to create validation PUMS in the Bay Area validation set. Thus, this procedure will be better when applied to real census tracts than the already good results shown in the validation.

Environmental Modeling

We have extended the meteorological model to treat situations where clouds are important. In a coastal environment, such as Portland, Oregon, low-level clouds from the ocean influence the wind and dispersion characteristics. Earlier versions of HOTMAC (High Order Turbulence Model and Analysis Code) formed clouds, but it didn't treat the effect clouds have on radiation. To extend the model to treat clouds properly, we have revised our radiation transfer routines to describe the effects clouds have on heating and cooling in the atmosphere and on preventing sunlight from reaching the ground. We incorporated a subroutine that had been used in a one-dimensional version of HOTMAC and modified it to treat radiation transfer through clouds to the surface of the ground. The improved model produces plausible results and runs reliably, but requires further testing.

We have compiled the evaporative emissions code EVAP 3.0 and run it in a stand-alone mode. We have determined an interface between the trip planner and the EVAP code. The EVAP code uses a time-off and a time-on matrix and we can use the planner to generate these two matrices for each cell in the air chemistry model. This will give an aggregate evaporative emissions compatible with MOBILE5. We could disaggregate by constructing the matrix for each vehicle type and then doing the calculation for each vehicle type. This would require more data on individual vehicle characteristics.

We have received Sierra Research's VEHSIME code, which we will use for the initial emissions capability within TRANSIMS. We have begun examining VEHSIME to understand how to interface its models with the vehicle output from TRANSIMS.

Further Information

For further information about the TRANSIMS program, please contact:

Dr. LaRon L. Smith
Los Alamos National Laboratory
Mail Stop F606
PO Box 1663
Los Alamos, New Mexico 87545
Phone: 505-665-1286
Fax: 505-665-0879
E-mail: llsmith@lanl.gov

Table of Contents

To subscribe to this free newsletter send an e-mail to TMIP@tamu.edu or contact Gary Thomas at (ph.) (979) 458-3263, (fax) (979) 845-6001, (mail) Gilchrist, Room 112, Texas Transportation Institute, Texas A&M University System, 3135 TAMU, College Station, TX 77843-3135