The National Academies

NCHRP 08-143 [Active]

Guide to the Application of Spatial Segmentation on Travel Time Reliability Measures

  Project Data
Funds: $200,000
Staff Responsibility: Jennifer L. Weeks
Research Agency: Cambridge Systematics
Principal Investigator: Richard Margiotta
Effective Date: 10/18/2023
Completion Date: 10/17/2025

Travel time reliability measures create a consistent means of comparing the performance of different highways in the network. Travel time reliability measures inform decisions regarding highway capital and operating investments and facilitate accurate public reporting of highway travel times and performance. Additionally, travel time reliability is a required federal performance measure for state departments of transportation (DOTs) and large metropolitan planning organizations (MPOs). 
Travel time reliability measures are affected by the way highway corridors are divided into segments for data collection, analysis, and reporting. Corridors with fewer segments may “average out” the impacts of congestion “hot spots” along a corridor, creating less reliability in practice. Shorter and more intentionally defined road segments may have the effect of creating more predictable and consistent reliability measures by isolating the impacts of places that experience more or less episodes of congestion. However, the travel time reliability measures calculated for longer corridors with many “hot spots” can be less certain and comparisons of reliability measures calculated for roads within a network cannot always be trusted.
Typically agencies obtain travel time and speed data from third-party probe data suppliers who use predetermined segments. To improve travel time reliability measures, practices, and reporting, transportation practitioners need direction on the application of methods for supplementing these data using segmentation and aggregation to produce the most consistently reliable measures, ones that can be compared across the network and used for public communication and investment decision-making.
The objective of this research is to develop a guide for designing, modeling, and applying roadway segmentation in travel time reliability measurement to generate improved reliable predictions across similar roadway contexts. At the minimum, the research shall:
1. Identify different segmentation and aggregation methods for measuring travel time reliability in use by state DOTs, MPOs, and probe vehicle data providers across the nation.
2. Evaluate the variability in travel time reliability measures using different segmentation or aggregation methods appropriate for application in different roadway networks and contexts, taking into consideration roadway type, local density and environment, and temporal and geographic contexts, as appropriate.

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.

STATUS: Contract is active starting 10.18.2023.

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