Incorporating Travel Time Reliability into the Highway Capacity Manual (2014) / Chapter Skim
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Pages 111-119
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From page 111... ...
111 C h a p t e r 8 This chapter recommends the next steps to carry forward the results of this research. The following topics are addressed: • Defining reliability levels of service; • Implementing the L08 research; • Identifying freeway facility research needs; and • Identifying urban streets research needs.
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112 southbound approach for the Seattle facility is "unreliable" 11.1% of the time (i.e., its reliability is 88.9%)
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113 Option 3: Freeway Reliability LOS Based on Most-Restrictive Condition Options 1 and 2 are predicated on providing a distribution of the percentage of time the facility is unreliable, rather than assigning a single "grade" to define a highway's LOS. Although the distribution is highly useful for analysts, it may confuse nontechnical audiences who are used to using a single LOS value.
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114 Generally speaking, all SMS measures can be converted to TTI for consistency. LOS can be defined on the basis of the full distribution of TTI; on the fraction of time TTI exceeds a given value (associated with LOS F)
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115 However, creating a distribution rather than a single LOS value can be difficult to communicate to nontechnical audiences (a major use of the LOS concept)
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116 STREETVAL engines, thus executing the HCM2010 calculations in an automated fashion and processing the results for reliability reporting purposes. Although not part of the L08 project, a natural extension of the computational engines and other tools would be the development of a more user-friendly, integrated software tool that could execute the files faster than the Excel-based computational engines.
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From page 117... ...
117 and the month of the year; as such, it accounts for some implicit correlation between, for example, weather and demand (e.g., more snow in the winter and generally lower traffic demands)
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118 Truck Pick-Up and Delivery Lane and shoulder blockages resulting from truck pick-up and delivery activities in downtown urban areas can be considered like incidents in terms of the randomness of their occurrence and duration. The dwell time for these activities can range from 10 min to 20 min.
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From page 119... ...
119 Wet-Pavement Duration The findings from one research project indicated that the time required for pavement to dry following a rain event is a function of temperature. Drying time was found to decrease with increasing temperature.
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