Establishing Monitoring Programs for Travel Time Reliability
Within the second Strategic Highway Research Program (SHRP 2), Project L02 focused on creat- ing a suite of methods by which transportation agencies could monitor and evaluate travel time reliability. Creation of the methods also produced an improved understanding of why and how travel times vary and the factors that create that variation.
This final report provides a brief narrative about what reliability is and how it can be measured and analyzed. A general finding is that reliability is best described by creating holistic pictures like probability density functions (PDFs) and their associated cumulative density functions (CDFs). PDFs are helpful for identifying multimodality or the existence of multiple operating conditions within the data being examined (Barkley et al. 2012; Guo et al. 2010; Fraley and Raftery 2009). CDFs are helpful for seeing if progress is being made in making a system more reliable or for comparing the reliability of one system against another.