Guide to Establishing Monitoring Programs for Travel Time Reliability (2014) / Chapter Skim
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11 This guide describes how to develop and use a travel time reliability monitoring system (TTRMS)
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12 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY information about the influencing factors, to create a credible picture of how well the system is performing at the present time and in the past. The payoff is better reliability.
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13 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Figure 1.2 shows the four key information flow steps a TTRMS must execute to fulfill its purpose as a decision support tool. First, the TTRMS needs to effectively measure travel times.
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14 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY causal list used by the Federal Highway Administration to describe why congestion arises and breaks these sources into the seven major influencing factors (two internal and five external) shown in Figure 1.3.
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15 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY CONTEXT WITHIN STRATEGIC HIGHWAY RESEARCH PROGRAM 2 Reliability is one of the four focus areas of the Strategic Highway Research Program (SHRP) 2, authorized by Congress in 2006, and its purpose is to "reduce congestion and improve travel time reliability through incident management, response, and mitigation" (1)
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16 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Figure 1.4. Reliability monitoring system overview, with boxes for modules and circles for inputs and outputs.
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17 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY HOW TO USE THE GUIDE Agency staff can read this guide to understand what a TTRMS can do and what features make the most sense for their own situation. For example, from which sources can an agency collect data?
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18 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY system has failed. As Elefteriadou and Ciu (3)
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19 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY performance levels to be achieved on the segments and routes, consistent with Ebeling (4)
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20 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY disutility functions that compare the ATRs one at a time with their corresponding DTRs and then sum the results. Service providers want to see if different ways to operate the system would be likely to produce better alignment between the ATRs and DTRs (or if capacity investments are needed)
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21 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY TRIP-MAKING CONCEPTS Several trip-making concepts are important in understanding the material presented in this guide. The first and most important concept is that trips made by persons and packages are the fundamental events on which travel time reliability is focused.
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22 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY PROBABILITY DENSITY FUNCTIONS Much of the material presented in this guide emphasizes the creation and analysis of PDFs to describe the distribution of travel times and travel rates and to compare the performance of one facility with another or one operating condition with another. These distributions are often presented three ways.
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23 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY The second way in which these distributions are presented is via a PDF. Figure 1.8 shows the corresponding PDFs for the three conditions.
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24 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Figure 1.9. CDFs under various regimes (operating conditions)
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25 GUIDE TO ESTABLISHING MONITORING PROGRAMS FOR TRAVEL TIME RELIABILITY Since the word mode is used in other ways in transportation, in this guide the word regime is used instead of mode to describe these various operating conditions (or subconditions)
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