PHASE I
Task 1. Literature Review. Conduct a comprehensive critical literature review documenting the theory and practice of travel time reliability measurement by the transportation industry.
Document the literature review, including listing all sources, data collected, and information gained for inclusion in the Interim Report (Task 5).

Task 2. Synthesis of Current Practice. The team will develop a brief survey to be administered to State DOTs, local traffic engineering departments, and selected MPOs to identify, synthesize,
and document the current state of practice with respect to using different methods of segmentation to derive travel time reliability measures. Points of contact for the survey will be
identified by consulting with the TRB Committee on Performance Management (ABC30), the quarterly National Performance Management Research Data Set (NPMRDS), and State and 
MPO published performance reports for reliability segmentation treatment. The list of potential survey recipients will be shared with NCHRP for review and comment. After the initial
responses are received from these points of contact, the research team will follow up with phone calls to obtain more detail as needed.

Deliverables: 1. The survey recipients, questions, and survey results shall be developed and shared with the panel for their review and input. 2. The completed survey shall be documented into a technical memo to be integrated into the Task 5 interim report.

Task 3. Analyze data and information collected in Tasks 1 and 2 for its practical application by the industry presented in a manner that easily distinguishes the effects of different roadway
segmentation strategies to support different analytical and reporting purposes. The criteria to be used will include a. technical rigor; b. applicability to a range of reliability measures and
measure types; and c. pertinence to a range of applications using travel time reliability, including but not limited to performance reporting, project planning, and before/after project evaluations.

Deliverable: Summary memo for integration into the Task 5 interim report.

Task 4. Identify a short list of best practices and/or lessons learned from the industry for integration into the guide and other instructional products recommended by the research team in
the subsequent phase of work.

Deliverable: Summary analysis of Tasks 1-4 with a focus on best practices and other lessons learned.

Task 5. Develop an Interim Report documenting the process and results of Tasks 1–4. The interim report will be presented to the panel at an in-person or online meeting to be convened by
NCHRP. The report will also contain a Phase II work plan as an experimental design for testing and an
outline for the final deliverable. The parts are described below.

An Experimental Design will be prepared for the case study analysis in Phase II. The Experimental Design will be based on establishing conditions to study in the field. Two rural and
two urban settings be studied with multiple types of facilities in each setting. These locations will be proposed to the Panel and a final list drafted in consultation with the panel and NCHRP at the
Interim Meeting.

Prior to the main testing, the research team shall conduct several pretests to resolve several observed issues related to calculating reliability performance measures, including reference or
free-flow conditions, time periods for reporting, and issues related to incorporating volume into performance measures and expectations. 

Reference and Free Flow Conditions: Many measures, such the Buffer Time Index, Planning Time Index, and delay require a reference value, the deviation from which defines the measure.
However, setting this value has proven to be contentious. Travel time under free-flow or “ideal” conditions is commonly used, for example, in the HCM. This approach can create a serious
disconnect between delay and reliability for freeways versus signalized highways. If free-flow conditions for signalized highways are based on midblock speeds, as recommended by the HCM,
the performance measures do not account for the fact that the presence of signals introduces some delay even at very low volumes, resulting in delay and reliability values that are noticeably
higher than for freeways.

Time periods for reporting. Traditionally, the peak hour has been used as the time period for capturing congestion, yet congestion is rarely confined to it. Promoting standard time periods
would be useful for comparing across locations. Further, a method for defining locally based time per iods would allow agencies to customize their performance reporting.

Traffic Volumes. The research team will seek to understand how weighting performance measures by volumes influences reliability performance measures. Except for certain types of “companion” measurements of volume. The lack of volume limits certain types of performance measures from being developed, including delay and the failure-based measures used for
reliability (e.g., percent of vehicle-miles traveled that occurs below a threshold speed). It also means that weighting cannot be done when aggregating reliability measurements across facilities
that may have radically different volume profiles.

The second key component of the Interim Report will be an outline of the final guide. The guide will provide a summary of the research findings and recommendations for reliability segmentation and associated computation for a variety of applications, including:
• Long range planning, especially in conjunction with travel demand models.
• Corridor planning.
• Analysis of design alternatives.
• Operational analysis and deployment planning.
• Performance reporting.
• Project evaluations.

NCHRP will convene a panel meeting to discuss the contents of the Interim Report and proposed
work to be conducted in Phase II. The research team shall respond to all comments received on
the draft Interim Report and revise the report accordingly.

NCHRP authorization is required prior to initiating Phase II.

Deliverables: Draft Interim Report, Interim Panel Meeting, Final Interim Report

PHASE II
Task 6. The research team shall identify candidate segmentation approaches for testing. The
research team shall test a minimum of three segmentation methods:
• The Strategic Highway Research Program (SHRP)2 L03/Highway Capacity Manual (HCM)
approach based on bottleneck or traffic generator breakpoints.
• FDOT Sourcebook method based on traffic level and situational characteristics.
• Queue-based distances for existing conditions.

Other methods will be identified by the agency and literature reviews in Phase I and proposed in the Interim Report for discussion with the panel at the Interim Meeting.

Deliverable: Draft Experimental Approach memo; Final Experimental Approach Memo. 

Task 7. Pilot test at least 3 segmentation approaches as described in Task 6 using case study data and highway project examples. The case studies should demonstrate the impact of choices made
on the length of segments, selection of segment breaks, and other segmentation issues on the reliability of travel time performance measures. The analysis should illustrate any issues
experienced by the agencies in their application as well as measure the extent of impact on the travel time reliability measures that come from their use.

Additionally, the testing phase will include a reconciliation of procedures for computing travel time reliability measures. There are two basic approaches that shall be tested against a reasonable
subset of case study locations:

1. Compute reliability measures for short spatial units, then average them to higher aggregation levels (using the vehicle-miles traveled (VMT)- or length-weighted average).
2. Compute travel times over the entire spatial unit of interest (end-to-end) for each time in the data, then use the resulting travel time distribution to compute reliability measures.

Deliverable: Case study analysis memorandum describing the process and outcomes of the case studies.

Task 8. Prepare a guide and supplemental products identified in the approved Phase II work plan.

Task 8.1 Prepare a draft guide for panel review and comment. This will be prepared in accordance with the direction provided in the CRP Procedural Manual (June 2023).

Task 8.2. Prepare and submit the final guide and all other deliverables required to complete the publication process, as provided in the CRP Procedural Manual (June 2023). This will include a
complete and specific written response to all panel comments, including how the deliverableswere changed to respond to a given comment.

Products of this research shall at a minimum include:

1. A practical guide providing comprehensive instruction on the design and implementation of segmentation and aggregation to support a variety of travel time reliability measurement contexts;

2. A matrix or summary graphic documenting the benefits and impacts of distinct methods, both in use and/or proposed through this research, for assessing and documenting travel time reliability under different contexts;

3. A process diagram, graphic, or summary depiction of a recommended process for defining and using appropriate segments for the purposes of measuring travel time reliability for different purposes;

4. A research report documenting the research process, summarizing and presenting all data collected, methods used, analysis of methods, and resultant recommendations or guidelines for implementation by agencies;

5. An implementation plan specifying an approach to facilitating the application of the research by the transportation industry.