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Center Identification Number:  77805   

Project Title:  Quantifying Net Social Benefits of Vehicle Trip Reduction Impacts to Make Existing Road Infrastructure Perform Better– Guidance for Customizing the TRIMMS Model to Aid Local, Regional and State Decision Makers   

Co-Principal Investigators:

Sisinnio Concas, Senior Research Associate
Phone: 813-974-7760

Philip L. Winters, TDM Program Director
Phone: (813) 974-9811


Center for Urban Transportation Research
University of South Florida
Fax: 813-974-5168

External Project Contact:     

Amy Datz
Public Transportation Office / Transit Planning
(850) 414-4239


I.  Start and End Dates

Start Date: January 24, 2008                Expected End Date: February 28, 2009

I.  Project Objective/Problem Statement

According to a General Accountability Office report released in late July 2007, “Three broad factors inhibit efficient use of roads and highways: design and operation factors; the revenue-raising structure; and a limited focus on selecting projects that produce the highest net social benefits in the current decision-making process.” On the latter factor, the GAO noted that “there is a limited focus in the current decision-making process on selecting projects that will produce the highest net social benefits. Decision makers also are limited in their ability to identify and put in place infrastructure investments that would produce the highest estimated social benefits because the current decision-making process is compartmentalized by mode and is not driven by economic analysis.” Another example of the need for understanding the net benefits can be found in the 2006 Congestion Mitigation and Air Quality Improvement (CMAQ) Program Interim Guidance. This guidance provides explicit guidelines for program effectiveness assessment and benchmarking by calling for a quantification of benefits, as well as disbenefits, resulting from emission reduction strategies for project selection and evaluation. In a partial attempt to quantify the net social benefits, an increasing number of state, regional, and local agencies are attempting to measure the congestion and emissions impacts from transportation demand management (TDM). In addition, such agencies seek to assess if the strategies have met their performance-based planning standards or established goals. With funding from the Florida Department of Transportation and the US Department of Transportation, the National Center for Transit Research at CUTR at the University of South Florida recently developed TRIMMS (Trip Reduction Impacts for Mobility Management Strategies), the country’s first practitioner-oriented sketch planning tool. TRIMMS used national values for cost externalities, as well as fare and travel time elasticities for model parameters. The model allows for customization of these values. This proposed research project would further enhance TRIMMS by allowing regional customization of default benefit and cost parameters. The enhancement would allow a wider range of default values needed for the analysis, specifying under what conditions or ranges of conditions the values could be considered reliable or appropriate. This would improve the ability of decision makers to identify and put in place transportation investments that would produce the highest estimated social benefits. TRIMMS also applies an economic analysis approach comparable to those used for infrastructure investments thus reducing the modal bias identified by the GAO. Further, for agencies that wanted to tailor default values to their areas, the research would provide sample data collection and measurement tools that agencies could use locally. Through its reliability and consistency, this package of guidance materials could enhance the accuracy and comparability of impact estimates produced across the state and the nation.

II.  Objectives/Tasks

TRIMMS permits program managers and funding agencies like FDOT to make informed decisions on where to spend finite transportation dollars based on a full range of benefits and costs.  The model allows some regions to use local data or opt to use defaults from national research findings, select the benefits and costs of interest, and calculate the costs and benefits of a given program.  A key strength of this model is its wide range of benefits and costs that can be selected for the analysis.  The model’s flexibility and robustness allows it to be adopted by agencies throughout the country.

The objective of this study is twofold. First, a collection effort will be conducted to obtain cost and benefit parameters to allow model customization at a regional level.  In addition to this data collection effort, the model will be updated and refined to allow the incorporation of regional parameters.

Finally, this project will provide the research and documentation necessary to help professionals to use the model by selecting the appropriate cost parameters, providing a reference to sources where o such parameters can be obtained, and by offering general guidance on how to incorporate data already at their disposal.

Task 1:  Cost-Benefit Parameters Collection and Analysis

The current version of TRIMMS makes use of cost-benefit parameters culled from a literature review of benefits and impact of TDM initiatives at the national level. Although the model allows updating these parameters to account for changes in cost of living, it does not differentiate between regional areas across the U.S.  

The objective of this task is to update the cost-benefit parameters obtained and used when TRIMMS was first developed to take into account differences that exist between geographical areas in terms of congestion (e.g., Miami vs. Tallahassee) and population density levels. 

As part of this task, an initial review of current TDM evaluation studies will be conducted to cull and analyze cost-benefit parameters being employed and to adapt them to TRIMMS.  Since TRIMMS estimates the costs and benefits of TDM using the value of a trip removed as a benchmark measure, these costs will have to be adapted to the model’s workings.

This task will be accomplished by both the Principal Investigator (PI) and Co-PI, with the assistance of a graduate student.  The role of the graduate student will be to cull studies and empirical investigations, and prepare a spreadsheet collecting all cost-benefit parameters.  The role of the PI will be to supervise the student’s activities, review the studies and analyze the cost-benefit parameters for consistency and usability.

Task 2:  Cost and Travel Time Elasticity Parameters Collection and Analysis

At the core of TRIMMS is the capability to estimate mode share changes.  The modeling framework allows capturing a broader range of trade-offs that users constantly face and is capable of quantifying impacts on travel patterns by using prices as the direct drivers of travel demand.  Furthermore, the approach is able to take into account how individuals re-adjust over time in their trade-offs.  The estimation of modal share changes brought about by TDM strategies affecting the generalized time and monetary costs of travel are based on a constant elasticity of demand function.  This function relies on cost and travel time elasticity parameters.

The objective of this task is to revisit each mode demand function to incorporate additional elasticities that allow further disaggregation of impacts.  For example, the transit travel demand function will be expanded to account for the different impact a fare change exerts, depending on time of the day (peak and off-peak) as well as the segment of the population using such mode.

The PI will be conducting and directing this task, with additional support from the graduate student.  This task could also represent an opportunity for a graduate student to get hands-on exposure to the microeconomic theory of travel demand which should benefit the student’s future employer and clients.

Task 3: Guidance to Update and Customization of Cost-Benefit Parameters

The objective of this task is to summarize the results of Task 1 and Task 2 into a technical document to help professionals to use the model and the cost parameters, and in addition provide a reference to sources where such parameters can be obtained.  It is anticipated that this document will appear as an appendix in the final report.

Task 4: TRIMMS Model Update to Version 2.0

The objective of this task is to update the TRIMMS model to allow more customization, and to clearly differentiate between analysis at the regional and employer-site levels.  Furthermore, the model module that evaluates the impact of employer support programs will be revised.  This includes a refinement of the employer support parameters (e.g., emergency ride home programs) previously estimated by employing panel data regression analysis of commuter trip reduction programs.

This will result in version 2.0 of TRIMMS.  It is in the intention of the PI to include in the new version an extended capability to allow for Monte Carlo simulation of the impact estimates.  Monte Carlo methods are useful for modeling events with significant uncertainty in the values of inputs. For example, such methods may be used  by the insurance industry for calculating risk. This will consist of an embedded module that permits sensitivity analysis, a feature to date not present in any other spreadsheet application of this kind.

This task will be conducted by the PI, who is the model inventor and who possesses the necessary Visual Basic language skills to create the simulation module.

Task 5:  Final Draft and Final Report

The objective of this task is to summarize the efforts of Task 1 through Task 4.  This task will be accomplished by the principal investigator (PI) and the co-PI.

III. Deliverables

Progress Reports – Progress Reports will be submitted on a quarterly basis to the Research Center for processing. Reports will include the following sections: 1. Work done in period being reported 2. Work to be done in next period 3. Requested modifications to scope, budget, or schedule, as appropriate 4. An updated schedule

Draft Final Report – An electronic copy of the draft final report will be submitted to the project manager no later than sixty (60) days before the end of the contract to allow sufficient time for editing and revisions. The draft final report will be edited for grammar, clarity, organization, and readability prior to submission to the Department for technical approval. The editor providing the review will sign a cover sheet attesting to such review prior to submission.

Final Report – Thirteen (13) hard copies of the final report, one (1) electronic version of the final (Word), and one (1) electronic version of the summary (Word) will be provided to the Research Office.

Other deliverables – Additional deliverables for this project will include the following: Spreadsheet and/or web-based version of TRIMMS 2.0 Note: All materials printed under the contract will have the FDOT, USF, NCTR/CUTR logos.


IV.  Project Schedule

V.  Project Budget

Exploration of a Shift in Household Transportation Spending from Vehicles to Public Transportation

Budget Categories


Center Director Salary

$   1,912

Faculty Salaries

$ 49,649

Admin. Staff Salaries


Other Staff Salaries

$      525

Student Salaries

$   7,965 

Staff Benefits

$ 28,253

Total Salaries and Benefits

$ 87,710


$   2,655

Permanent Equipment


Expendable Property/Supplies

$     544

Domestic Travel


Foreign Travel


Other Direct Costs


Total Direct Costs

$ 90,909

Indirect Costs

$  9,091

Total Costs

$ 100,000

Notes: This budget does not reflect any federal participation. The project team will include faculty, students, and secretarial and other support staff who will work directly on the project and whose costs are reflected in the direct costs of the project as listed above. Budget requests includes salaries for clerical and administrative staff, postage, telephone calls, office supplies, general purpose software, subscriptions, and/or memberships.

VI. Equipment

No equipment is envisioned to be purchased under this project.

VII. Travel

No travel is required.

VIII. Student Involvement

A graduate research assistant will carry out much of the work under the direction of the PI.

IX. Relationship to Other Research Projects

This study represents the next phase of a recently completed NCTR project (BD-549-26) and was identified as the #1 priority among 53 research needs identified by the Transportation Research Board Committee on TDM and Association for Commuter Transportation’s TDM Institute.

IX. Potential Benefits of the Project

This project will provide the research and documentation necessary to help professionals in the fields of transportation and urban design to bridge the gap between these separate disciplines. It will create a clearly defined and shared terminology and methodology that enables planners and designers to develop transportation solutions that take into account many community goals.  This work will culminate in a publication summarizing the study results, the methodology, and matrices setting out the findings in a readily accessible format.

National Center for Transit Research · at the Center For Urban Transportation Research · University of South Florida · 4202 E. Fowler Ave., CUT100 · Tampa, FL 33620-5375 · (813) 974-3120 · (813) 974-5168 · · Comments: