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From page 137...
... 135 5 SUMMARY This chapter summarizes the steps involved in developing a travel time reliability monitoring system (TTRMS) , starting with the various potential data sources and ending with metrics that can be used to assess performance.
From page 138...
... 136 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY STEP 1. COLLECT AND MANAGE TRAFFIC DATA The first step in the analytical process, illustrated in Figure 5.2, is to collect and store all types of traffic data.
From page 139...
... 137 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Management of the data from each of these detector sources follows the general methods outlined in Chapter 2. Vehicle-Based Sources Vehicle-based detectors collect data about specific vehicles, either when they pass a fixed point, as in the case of automated vehicle identification (AVI)
From page 140...
... 138 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Automated Vehicle Location Data AVL data collection sources provide perhaps the richest source of data in that they identify traceable paths for individual vehicles through a system. Chapter 4 presented the application of AVL data for travel time reliability analysis for two case studies: 1.
From page 141...
... 139 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Step 2A. Impute Missing Values A major challenge in producing useful travel time reliability performance measures is the reality that the data sources are often incomplete for a variety of reasons.
From page 142...
... 140 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Infrastructure-Based Sensors In this case, segment travel times are computed from either the measured or estimated speeds at each sensor. For double-loop detectors, the speeds are directly measured.
From page 143...
... 141 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Step 2C. Compute Route Travel Times The construction of route travel times, including their distribution from a set of segment-level observations, is significantly more complicated than simply adding travel times together (as can be done carefully when looking only at averages)
From page 144...
... 142 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Figure 5.4. Characterizing the observed travel times.
From page 145...
... 143 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Diego, which integrates incident data from the statewide Traffic Accident and Surveillance Analysis System, lane closure data from Caltrans, and weather data from the Automated Weather Observing System reported for San Diego International Airport. These examples are presented in Chapter 4 for the San Diego case study.
From page 146...
... 144 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY STEP 5. IDENTIFY SOURCES OF CONGESTION AND UNRELIABILITY Once route travel time calculations or distributions have been assembled, they can be analyzed in conjunction with nonrecurring event data to identify sources of unreliability, as illustrated in Figure 5.6.
From page 147...
... 145 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Statistical Approach The statistical approach involves two steps. The first step involves identifying outlying travel times for which explanations should be sought for the discordant values observed.
From page 148...
... 146 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY the San Diego case study. The Atlanta case study uses multistate models to inform on the reliability impacts of nonrecurrent congestion.
From page 149...
... 147 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY but it was the intent of the project to ensure that the data provided by the reliability monitoring system can be used for such purposes. CONCLUSION A TTRMS can be a powerful asset in the decision-making process for managing transportation facilities.

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