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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
