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CHAPTER 4 Data Compilation and Analysis of Existing Conditions 4.1 Introduction As part of the evaluation of the tools described in subsequent chapters, the study team conducted a data compilation and analysis of existing conditions. The team followed the approach described in the SHRP 2 Reliability Project L02 Guide to Establishing Monitoring Programs for Travel Time Reliability (the guide) to determine the factors affecting reliability on the two study facilities and to assess the relative contributions of these factors (ITRE et al. 2012). This analysis allowed the team to test the value of collecting, storing, and using nonrecurring event data from various sources to help explain causal relationships. Specifically, the study team used the following sections from the guide: ⢠Average Route Travel Times Based on Infrastructure Sensor Data ⢠See What Factors Affect Reliability (AE1) ⢠Assess the Contributions of the Factors (AE2) The study teamâs activities to date for each of these sections are discussed below. 4.2 Overview of the L02 Guide An earlier draft of the L02 guide (ITRE et al. 2012) describes how to develop and use a Travel Time Reliability Monitoring System (TTRMS). A TTRMS is designed to assist public agencies to monitor the performance of the transportation network and better understand the factors that influence variations in travel times on the network. By having a better grasp of how system reliability will change, given various events that occur, such as incidents, weather, special events, work zone closures, and surges in demand, public agencies can respond more effectively to mitigate the impacts of the event and provide the public with better traveler information. For example, a TTRMS may be able to provide a range of expected travel times to drivers given that a sporting event is taking place at a particular time of day. The guide has five chapters that describe the process of measuring, characterizing, identifying, and understanding the impacts of events that affect travel time reliability. In addition there are four appendices that provide detailed information as follows: ⢠Appendix A: Monitoring System Architecture presents examples of detailed data structures for the organization of various data sources and provides supporting detail for Chapter 2 (Data Collection and Management) of the guide. ⢠Appendix B: Methodological Details presents detailed discussions of the analytical methods that can be used to calculate travel time reliability measures from a variety of 42
