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CHAPTER 1 Background 1.1 Introduction The second Strategic Highway Research Program (SHRP 2) has been researching the critical subject of travel time reliability for several years. As part of this research, SHRP 2 supported multiple efforts to develop tools for evaluating travel time reliability and estimating the impact of projects on reliability. In particular, the SHRP 2 reliability projects developed several methods to help public agencies: ⢠Collect and analyze data on the variability of travel time, ⢠Diagnose problems, ⢠Propose actions or alternative mitigation strategies, and ⢠Test the impacts of solutions. A goal of this research was to find ways to demonstrate how operational strategies improve travel time reliability, which is highly valued by both the person and goods movement transportation markets: ⢠Travelers get frustrated when their trip travel times vary significantly. They either have to routinely plan for longer travel times or frequently arrive at their destinations later than planned. ⢠Truck drivers often do not have choices. They have to arrive at a certain time, so they must plan for a margin of unexpected delays, which reduces their productivity and increases costs. Operational strategies are critical to improving both mobility and travel time reliability on highways. These strategies generally can be implemented faster than larger system expansion projects, often do not require detailed environmental reviews, and generally cost much less. However, decision makers often defer operational investments, in part because of the limitations of existing tools. Examples of operational strategies used to mitigate traffic congestion and improve reliability include: ⢠Ramp metering, ⢠Auxiliary lanes, ⢠Improved incident management, and ⢠Improved traveler information. 16
