Issue Date: 2012-02-01
Overview: This is the fifth and final case study performed by the project team in order to validate the approaches to travel time reliability monitoring described in the Travel Time Reliability Monitoring Guidebook. The goal of each case study is to illustrate how agencies apply best practices in transportation performance monitoring and analysis. Typically, this includes monitoring system deployment, travel time reliability calculation methodology, and agency use and analysis of the data. However, in this use case, special focus is given to a new data source: vehicle probe data. In order to focus on practical issues associated with processing this data, no real-time travel time monitoring system or archived data user service was deployed as part of this case study. Rather, travel time reliability analysis was carried out offline, directly on the probe vehicle data set itself. This case study consists of the following sections:
- Monitoring System
- Methodological Advancement
- Use Case Analysis
- Lessons Learned
This monitoring system description section details the reasons for selecting New York as a case study site and gives an overview of the setting. It briefly summarizes the archived probe vehicle data source and the underlying road network to which it corresponds, and gives an overview of approach that the team took to analyze that data.
The section on methodology describes the steps necessary to obtain Probability Density Functions (PDFs) of travel time distributions along a New York City route based entirely on probe data. Critically, this probe data is sparse and few probe vehicle runs traverse the entire route. Techniques are presented to preserve the correlation in speed measurements on consecutive links while synthesizing the aggregate route travel time PDF from segments of multiple probe vehicle runs.
The Use Case Analysis section is less theoretical, and more site-specific. It is motivated by the user scenarios described in the Task 2/3 document, which are the results of a series of interviews with transportation agency staff regarding agency practice with travel time reliability. While the methodology section of this case study describes the steps necessary to process and interpret probe vehicle data, the use case section focuses on a specific application of this methodology. This case study contains a single use case that focuses on three alternative methodologies for constructing travel time probability density functions (PDFs) from probe data.
Lessons Learned summarizes the lessons learned during this case study, with regards to all aspects of travel time reliability monitoring: sensor systems, software systems, calculation methodology, and use. These lessons will be integrated into the final guidebook for practitioners.
Operations Area of Practice: Detection Systems, Communicating Reliability Information, SHRP2 Tools, System Performance Definition, Monitoring and Reporting, Travel Demand Forecasting
Organizational Capability Element: Reliability Predictive Models
Content Type: Case Studies & Lessons Learned
Role in Organization: Associate Engineer, CEO / GM / Commissioner, Director / Program Manager, Engineer, Manager / First Line Supervisor, Principal Engineer, Public, Researcher/Academic, Senior Engineer, Senior Manager, Technician, Transit Professional, Transportation Planner
Publishing Organization: SHRP2 Program