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The National Academies

SHRP 2 L33 [Active]

Validation of Urban Freeway Models

  Project Data
Funds: $499,979
Staff Responsibility: William Hyman and Stephen Andrle
Research Agency: Iteris, Inc.
Effective Date: 12/20/2012
Completion Date: 6/19/2014

Project snapshot. More details below.

Products
(Project Number)
Impact on Practice
Product Status
VALIDATION OF URBAN FREEWAY MODELS (L33)

A report that describes the effort to validate two urban freeway prediction models developed under SHRP 2 Project L03: (1) a simple one that just uses data on the mean travel time and (2) a more complex model that requires data on demand in relationship to capacity, lane hours lost due to incidents or work zones, and rain above a threshold. The report will also describe the enhanced models.
The L03 models are used in a number of SHRP 2 products and studies. The validation will increase user acceptance and confidence in the L03 models. The validation study may provide alternative prediction models, offering a user a choice of which ones to apply in a situation. This is quite likely to be the result of developing enhanced L03 models.
The project will be completed in mid-2014.

Reliability Focus Area
The major objective of SHRP 2 Reliability research is to greatly improve the reliability of highway travel times by reducing the frequency and effects of events that cause travel times to fluctuate unpredictably. The results of the research program should help local, state, and national agencies reduce travel time variability for travelers and shippers. The Reliability research plan addresses both recurring and nonrecurring congestion with an emphasis on nonrecurring congestion. The following seven potential sources of unreliable travel times (i.e., events that cause variable travel times) were identified: traffic incidents, work zones, demand fluctuations, special events, traffic control devices, weather, and inadequate base capacity.
 
The Reliability focus area targets travel time variation—that frustrating characteristic of the transportation system that means you must allow an hour to make a trip that normally takes 30 minutes. Not only is reliability an important component for travelers and shippers, it is also an area of the congestion problem in which transportation agencies can make significant gains even as travel demand grows. The seven sources of unreliability account for approximately half of the total delay. Reducing reliability-related delay will also result in fewer crashes, reduced vehicle emissions and fuel use, and other benefits. These benefits can be realized through a mix of leading-edge research into a better understanding of strategies and their consequences, new technology and practices, and reducing institutional barriers so that our existing knowledge can be more fully exploited.
 
The goals of the Reliability focus area are built around the first five of the seven sources mentioned above. Work on weather-related issues will be coordinated with the Road Weather Management R&D program under way at the Federal Highway Administration. Related research on inadequate base capacity being undertaken in the SHRP 2 Capacity focus area and elsewhere will be closely coordinated by SHRP 2 staff.
 
Project Background
Decision makers involved in evaluating how to best spend funds to improve travel time reliability need to know the outcomes in a way everyone understands. Decision makers also need to know that the benefits are larger than the costs and how to efficiently evaluate relevant alternatives. The projects that comprise the entire SHRP 2 Reliability research are intended to provide analytic methods and a framework for informing and making these types of decisions. A good example is the Reliability project that has developed a method and spreadsheet for evaluating a large number of different types of design improvements potentially capable of improving travel time reliability. A practitioner can enter values for parameters that describe the essential characteristics of the roadway and the design improvement. Then a spreadsheet will calculate travel time distributions before and after the design is implemented and numerous performance measures including the change in delay, accidents, different reliability metrics, and monetary estimates of benefits and costs. The key to estimating the effect of the improvement is a model set developed under SHRP 2 Project L03, “Analytic Procedures for Determining the Impacts of Reliability Mitigation Strategies,” This model is at the heart of the “before and after” calculations and helps provide many answers to questions important to decision makers, whether involved in operations management, planning, or project development.
 
The SHRP 2 Reliability Project L03, sought to develop technical relationships between reliability outcome measures and various strategies for reducing non-recurring congestion. The research involved many different types of investigation including identifying and recommending reliability metrics for research and general practice, identifying trends in reliability, estimating congestion by source (i.e. the causes of congestion), conducting before-and-after reliability studies, and performing cross-sectional statistical analysis on large data sets. The study sets out an experimental plan and devotes considerable attention to the processing of the data to develop the data sets which were used to develop simple models for predicting reliability and more complex ones that are a function of key variables. These important variables relate to highway characteristics, operational strategies, and a facet of weather. The simple set of models is referred to the “Data Poor” model in the Final Report and the more complex set, the “Data Rich” model.

Project Objectives
The objectives of this project are threefold. The first is to validate and enhance the most important models – the “Data Poor” and “Data Rich” models -- estimated on large data sets pertinent to urban freeways, which were developed under SHRP 2 Reliability Project L03. The second objective is to enhance the level of confidence of researchers and practitioners regarding models that can estimate the impact of various actions on travel time reliability. The third objective, through validation, is to promote acceptance and use of the L03 type of models for planning, programming, project development, design, systems operations, and further research.

Statement of Work
The scope of the L33 project is to validate the “Data Rich” and “Data Poor” models pertinent to urban freeways. This work requires a validation plan, data acquisition, as well as validation and refinement of the existing models. Recommendations for applying the validated and extended models are part of the scope. It is important to communicate to practitioners and researchers how the L03-type of models are useful for sketch planning and for more in-depth analyses that use inputs on causes of non-recurring congestion and the characteristics of specific urban freeway sections.
 
Tasks
The proposal must use a task structure to describe the approach and must provide a cost estimate for each task in the proposal. A brief description of possible tasks to be performed for project L33 is provided in this section of the Statement of Work. The objectives as reflected in the following tasks are considered essential, but proposers are invited to suggest different approaches that would accomplish the same objectives more effectively or efficiently. Also, proposals should identify and describe sub-tasks where appropriate.
 
Task 1. Background. Gather information that adds value to the background the contractor already has regarding SHRP 2. This task assumes that the contractor is already familiar with the L03 research -- background which may be acquired before or during the proposal development process. Examine relevant literature from the United States and other countries. The aim of this task is to identify important findings and lessons learned from the background information gathered that will help validate and extend the L03 models. Prepare and submit a Task 1 Technical Memorandum.
 
Documentation of the L03 research is found in the main body of the report and the Appendices A-H. Note that the “Data Poor” model to be validated is in Appendix H, which has superseded the “Data Poor” model in the body of the report.
 
Task 2. Validation Plan (Analysis and Data Collection). Develop coordinated analysis and data collection plans to validate the Data Poor and Data Rich Models. These plans should refine a detailed description of the analysis and data collection approach previously set out in the contractor’s proposal. Identify data sets that the contractor has in its possession or can access from public or private sources needed to validate L03 models (See notes on data sources).  A firm commitment and/or active involvement of organizations providing data would help achieve the project objectives. Estimate the costs of the data. Submit a Draft Task 2 Technical Report for review and comment, revise, and submit a Final Task 2 Validation Plan.
Task 3. Data Acquisition. Upon approval of the Validation Plan, acquire the data. Prepare a Task 3 Technical Memorandum that summarizes the data acquired, including metadata descriptions useful for the SHRP 2 Reliability Archive. Present the costs of acquiring each data set, the total cost and the balance of funds for analysis or to keep in reserve for additional data collection. Submit a Task 3 Technical Memorandum.
Task 4. Initial Validation. Perform validation analysis using the estimated Data Rich and Data Poor Models documented in the L03 Final Report (Chapter 7 for the Data Rich Models and Appendix H for the Data Poor Models). Conduct this initial validation so as to address both spatial and temporal transferability. Transferability implies being able to apply the models effectively to different urban areas, road geometric characteristics, system topology, climates, scales or temporal aspects of mitigation strategies.  Address the extent to which the models accurately predict the impact of mitigation strategies on travel time reliability on other urban freeways. Model validation should address the limitations of transferability, potential improvements for possible “repair” of these limitations, and the consequences of the remaining limitations for applying the models in practice. Consider performing the initial validation for a sufficient number of urban freeway sections in enough metropolitan areas to achieve the objective of promoting acceptance and use of the models. The sample size and approach to transferability in the Task 2 Validation Plan should recognize what can be accomplished within the project budget and duration. Identify potential improvements to the original L03 models. Prepare and submit a Task 4 Technical Memorandum and meet with the ETG.
Task 5. Enhancement. Beginning with the potential improvements identified in the previous task, develop, test, and recommend enhancements to the L03 models that would strengthen their predictive power and increase confidence in their use while continuing to meet the original requirements of Project L03. Investigate various functional forms, independent variables and coefficients. Consider different ways to account for recurring congestion in connection with the Data Poor Models. Consider improved ways to address lane hours lost and weather in the Data Rich Model. Present the recommended enhancements to the ETG in an appropriate meeting format and along with necessary revisions to the analysis and data collection plans (from Task 2) relevant to the enhancements. Obtain feedback and revise the planned enhancements as required. Upon approval to proceed, acquire any additional data necessary to perform the enhancements and estimate the enhanced models. Thoroughly document the enhanced models. Compare the enhancements to the original L03 models (i.e. those documented in the L03 Final Report and validated in Task 4). Describe how the enhanced models will help achieve the project objectives. Prepare and submit a Task 5 Technical Memorandum.
Task 6. Validation of Enhanced Models. Propose a suitable method to validate the enhanced models developed in the previous task. The method should be appropriate given the remaining funds and time to complete the project. Obtain approval from the ETG on the methodology before commencing the validation of the enhanced models. Prepare and submit a Task 6 Technical Memorandum. 
Task 7. Application Guidelines. Provide guidance to potential users of the models on how to achieve the objectives of this research in a Task 7 Technical Memorandum.
Task 8. Draft Report. Prepare a Draft Final Report on validation of the L03 research and submit within 90 days of the contract end date. Obtain and address, as appropriate, the comments from the ETG.
 
Task 9. Final Report. Prepare and submit a Final Report. Take into account the comments received on the Draft. Communicate with the ETG as required to address their comments.
 
Special Notes
 
1.     No member of the original L03 team – prime contractor, subcontractor, consultant, or individuals – may conduct the validation work for Project L33.
2.     Validation must occur on data different from that used in the L03 research.
 
3.     SHRP 2 Reliability Reports for L03 can be accessed at the following site: http://www.trb.org/StrategicHighwayResearchProgram2SHRP2/Public/Pages/RFP_L33_Resources_and_Reference_Material_620.aspx.  Information on projects related to L03 and L33 can be found at the SHRP 2 Reliability and Capacity websites: http://www.trb.org/StrategicHighwayResearchProgram2SHRP2/Pages/Reliability_159.aspx
4.     The proposal should contain a detailed description of the proposed Task 2 Validation Plan, both Coordinated Analysis and Data Collection plans.
5.     Data collected and used by the contractor for L03 must be turned over to the National Academies upon conclusion of the contract along with suitable documentation so that it can be stored and retrieved easily.  The National Research Council, the operating arm of the National Academies, shall have the right to duplicate, use, and disclose in any manner and for any purpose whatsoever all data, whether delivered to the National Academies or not, under the contract and to authorize others to do so. The Academies insists on protecting the privacy of individuals and the proprietary interests of firms while ensuring that the potential uses of project data by the Academies can be met.
6.     The data will ultimately be stored in the SHRP 2 Reliability Archive being designed, developed and implemented under Reliability project L13-A. The L33 contractor must work with the L13-A contractor to describe the data in accordance with any metadata standards that have been established under L13-A and to reflect such documentation in the Final Report.
 
Deliverables
 
Task 1 Technical Memorandum
 
Draft Task 2 Technical Memorandum
 
Final Task 2 Technical Memorandum
 
Task 3 Technical Memorandum
 
Task 4 Technical Memorandum
 
Task 5 Technical Memorandum
 
Task 6 Technical Memorandum
 
Task 7 Technical Memorandum
 
Draft Final Report: The draft materials should be submitted three months before the end of the contract to allow time for SHRP 2 review. 
 
Final Report

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