Incorporating Travel Time Reliability into the Highway Capacity Manual (2014) / Chapter Skim
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Pages 122-141
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122 This document provides guidance on using the FREEVAL-RL (FREeway EVALuation–Reliability) computational engine, which implements the freeway reliability analysis methodology developed in SHRP 2 Project L08.
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123 The computational engine is further designed to allow the user to revise input data following the completion of an analysis. This feature is intended to perform quick sensitivity or "what if" analyses of different demand scenarios or geometric changes to the facility.
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124 Figure A.2. FREEVAL-RL main user form, Step 1.
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125 the seed file. This user form, shown in Figure A.5, requires the following entries: 1.
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126 After the user clicks Yes in the input box, as shown in Figure A.6, the seed file is created using the total number of HCM segments and analysis (i.e., 15-min) periods.
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127 automatically execute the seed file, after which the main menu user form will be displayed. If the seed file has already been run (e.g., View Mode)
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128 Figure A.10. Revise input data.
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129 Step 3. Scenario Management The goal of this section is to provide guidance for users who wish to generate scenarios for reliability analysis.
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130 overall demand pattern input is displayed in a calendar format to show the configuration of demand patterns for the subject facility. In this step, the user configures similar seasons, months, and weekdays that will be combined within the same demand pattern.
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131 is made, a day can be added using the Add Excluded Day functionality.
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132 of hours in the 2 to 8 p.m. study period in which light snow occurred in January in Raleigh to the total number of hours in January between 2 and 8 p.m.
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133 impacts on facility operations. The CAF and SAF tables are currently filled with national default values in the HCM2010, but these values can be overridden by the user.
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134 If neither crash nor incident rate data are available, then a third path is to generate crash rates using the Highway Economic Requirements System (HERS) model.
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135 unique combination of demand, weather, and incident characteristics that is applied as matrices of DAFs, free-flow SAFs, and CAFs to the seed file data. As a general rule, the number of scenarios generated depends on a variety of factors, including the number of demand patterns selected, the diversity in weather activities, and the maximum number of lanes on any segment of the facility.
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136 As a last step, the adjustment factor file for FREEVAL-RL is invoked by clicking Step 5B: Generate FREEVAL Input file and Exit. The FSG then generates the FREEVAL input (adjustment)
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137 Summary Output file is saved, both in the same directory of the FREEVAL-RL. The Summary Output file consists of detailed information about each individual scenario and its respective output summary.
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138 Figure A.24. One-page summary report.
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139 Percent of VMT at TTI > 2: This failure criterion approximates the approximate number of trips at a travel time twice the free-flow travel time, which coincides with an average speed of half the free-flow speed. In addition to the statistics shown in Figure A.25, a series of output graphs for the facility reliability analysis are available (see Figure A.26)
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140 reduced by the amount of VHD that would have occurred from recurring sources of congestion (i.e., demand variability only)
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141 Reference Highway Capacity Manual 2010. Transportation Research Board of the National Academies, Washington, D.C., 2010.
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