Click for next page ( 33


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 32
32 C H A P T E R 4 Transportation Factors Background Literature et al., (2006) compile similar performance measurements specifically for freight transportation. The remainder of this Transportation agencies have been using performance mea- section discusses recent trends. sures to understand the implications of their investments on the transportation system for decades, and these practices stand as a model for incorporating the other factors included Key Findings in this performance measurement framework. Many perform- Performance measurement of transportation systems is ance measures used to plan, operate, and monitor transporta- increasingly operations-oriented. Performance measurement tion facilities today are descendents of measures conceived in of transportation systems over the last 50 years has been crit- the 1950s (Meyer, 2001), including: icized for being reflective of the values held by the engineers expanding capacity of the National Highway System (NHS) Mobility and reliability measures: (Hendren and Myers, 2006; Meyers, 2001). But as the NHS Annual average daily traffic per lane-mile; is all but built out, the focus of engineers has shifted from Average travel rate (minutes per mile); construction to operations. Marginal benefits of operational Nonrecurring delay; improvements are typically much smaller than those of Incident-related delay; capacity improvements, thus new measures are needed to Travel time index (median reliability measure); more accurately reflect travel characteristics. Recent literature Planning time index (95th percentile reliability measure); strongly supports this trend (Cambridge Systematics, Inc., and 2007; Brydia et al., 2007; Randall, forthcoming; Cambridge Percentage of vehicle miles of travel under congested Systematics, Inc., 2005). conditions. Performance measures must be viewed from both system Safety measures: and user perspectives. The literature and feedback from Number and rate of fatalities and injuries; and practitioners have indicated a trend toward measures that Number of crashes by type, including run-off-the- capture how customers experience the transportation system road, pedestrian, heavy-vehicle, impaired-driver, repeat- (Hendren and Meyers, 2006). Customer-oriented perform- offender, uninsured-driver, and unlicensed-driver. ance measures, including random sample surveys of travel- Infrastructure condition and deficiency measures: ers, web feedback, utilization of traveler information services, Average ride quality; press clippings, and media editorials have been used to gauge Percentage of asset length or count by condition; the quality of the customer experience (Adams et al., 2005). Remaining life; Though these outcome measures are important, output mea- Bridge health index; and sures such as speed, travel time, delays, and number of acci- Bridge deck condition. dents remain relevant. Perspectives from both the system and the user are needed (Cambridge Systematics, Inc., 2007; Adams These and many other traditional system-related measures et al., 2005; Shaw, 2003). are discussed at length in the literature (Cambridge Systemat- Measures of reliability are growing in importance for ics, Inc., 2000; Cambridge Systematics, Inc., 2007; Brydia et al., both passenger and freight travel. Passengers willingly accept 2007; Shaw, 2003; Cambridge Systematics, Inc., 2005). Harrison reasonable regular and predictable delays. Users are particularly