Overview
As part of the SHRP 2 program, project L02 focuses on measuring, monitoring, and recording travel time reliability (TTR) information. Through its guidebook, case studies, and demonstration software the project will help operating agencies develop systems – hardware, software, and strategies – that can monitor travel time reliability and convey information to customers and other data users.
In this first progress report is useful to begin by considering the definition of travel time reliability and how to measure it. While no consensus yet exists, Elefteriadou and Xiao (2007) have provided a good starting basis via their study of TTR definitions. As they discerned, Ebeling (1997) provides a useful basic idea, defining reliability as “the probability that a component or system will perform a required function for a given period of time when used under stated operating conditions. It is the probability of a non-failure over time.” This is a widely accepted definition that makes itself manifest in mean-times-between-failure (MTBF) for devices, repeatability expectations for measurement systems, validity measures for testing protocols, and quality control tools for manufacturing processes. It is slightly different from the idea of consistency, which has to do with the absence of variance.