The National Academies Press

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From page 10... ... "Travel time" and "delay" and the variability in those two quantities are key determinants of mobility and reliability. A system of mobility and reliability measures should be developed only after an examination of the uses and audiences to be served, the consideration of program goals and objectives, and identiﬁcation of the nature or range of likely solutions. Read the entire page →
From page 11... ... Use cost-effective methods to collect and/or estimate data Using readily available data or data collected for other purposes is a method of maximizing the usefulness of any data collection activities. Focusing direct data collection on significant problem areas also may be a tactic to make efficient use of data collection funding. Read the entire page →
From page 12... ... It can be described by accessibility maps and statistics and travel time contours that illustrate the areas that can be traveled to in a certain period of time. Descriptions of transit routes or special transportation services also can be used to identify locations where mobility and reliability are possible by more than private auto modes. Read the entire page →
From page 13... ... Travel speed-related measures can, however, be estimated as part of many analysis processes currently used. The ultimate implementation of a set of timerelated mobility and reliability measures in most urban areas will probably rely on some estimating procedures along with archived data. Read the entire page →
From page 14... ... . 2 Can be computed as a weighted average of all sections using VMT or PMT. Read the entire page →
From page 15... ... 2.2) Travel Time Index Freeway TravelRate Freeway = Free-flow or Posted Speed Limit Rate Freewa × y Peak Period VMT ⎡ ⎣ ⎢⎢⎢ ⎤ ⎦ ⎥⎥⎥ + Principal Arterial Street TravelRate Principal Arterial Street Free-flow or PostedSpeedLimit Rate × Principal ArterialStreet PeakPeriod VMT ⎡ ⎣ ⎢⎢⎢⎢⎢ ⎤ ⎦ ⎥⎥⎥⎥⎥ Freeway Peak Period VMT +Principal Arterial Street Peak Period VMT Delay per Traveler (annual hours) Read the entire page →
From page 16... ... The Planning Time Index is computed as the 95th percentile travel time divided by the free-flow travel time as shown in Equation 2.4. Read the entire page →
From page 17... ... These are discouraged as performance measures, as they are not readily understood by nontechnical audiences nor easily related to everyday commuting experiences. The 90th or 95th travel time, or indexes such as the BI or Planning Time Index, are recommended as simpler ways to express the variability of expected travel time in a way that travelers can relate more directly to their travel expectations or experience. Read the entire page →
From page 18... ... = The mean of the highest 20 percent of measured travel times; and MeanTime = The computed mean of the measured travel time. For example, if the mean travel time of the slowest 20 percent of trips in a corridor is 90 minutes and the mean travel time of all trips in the same corridor is 60 minutes, the Misery Index is calculated as (90/60) Read the entire page →
From page 19... ... The target travel time can be differentiated by the purpose of the travel, the expectation for each mode within the transportation system, the type of activity, and the time of day. It should be inﬂuenced by community input, particularly on the issue of the balance between transportation quality, economic activity, land use patterns, and environmental issues. Read the entire page →
From page 20... ... The concept can be used in the same manner that a target condition is implemented by both planners and operators. 2.7.5 How Does the Target Travel-Time Index Relate to the Computed Measures? Read the entire page →
From page 21... ... Special events and tourism activities also are situations that may generate interest in a rural analysis. As mentioned previously, continuous data sources provide speed (travel time) Read the entire page →
From page 22... ... For a special event, and possibly for a tourism activity/season, portable readers also could be installed to monitor mobility and reliability along rural corridors of interest. 2.10 The Right Measure for the Analysis Area Exhibit 2.6 summarizes the mobility and reliability measures that should be used for several types of analyses and for different size areas or modal combinations (6, 1) Read the entire page →
From page 23... ... . Travel time and speed measures, and data and estimating techniques used to create them, are ﬂexible analysis tools. Read the entire page →
From page 24... ... The amount of corridor or areawide person-travel that occurs in conditions worse than the locally determined targets can be used to monitor progress toward transportation goals and identify problem areas. 2.12.2 Relationship to Door-to-Door Travel-Time Measures The measure of system performance closest to the concern of travelers is door-to-door travel time. Read the entire page →

From page 10...

... "Travel time" and "delay" and the variability in those two quantities are key determinants of mobility and reliability. A system of mobility and reliability measures should be developed only after an examination of the uses and audiences to be served, the consideration of program goals and objectives, and identiﬁcation of the nature or range of likely solutions.