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target travel rate for goods movement over the corridor of in- ments where new modes or facilities are not realistic options
terest. If continuous data sources are available (e.g., toll tags or and even the operational improvements will be limited. These
cellular telephone), the BI also could be computed for freight analyses may proceed using HCMl-type procedures. Total
carriers. Prior to real-time systems, estimation measures could delay, delay per person, and travel-time difference are most use-
be used to estimate delay for goods movement. ful for intersections or individual locations due to problems
Special events and tourism also may invite mobility and identifying the length needed for the rate-based measures.
reliability analyses in a rural area. If real-time equipment Larger scale analyses, where more detailed analytical tools
already is installed, it could be used to obtain travel rate infor- are used and a wider choice of improvement options is con-
mation to compare to a target travel rate. Delay also could be sidered, are more frequently identified as mobility or relia-
computed. For a special event, and possibly for a tourism bility studies. The analysis and presentation of mobility and
activity/season, portable readers also could be installed to reliability data can be accomplished by the TTI, BI, TRI, total
monitor mobility and reliability along rural corridors of delay, and accessibility as primary measures. Secondary
interest. measures also may be used for cumulative analyses of several
improvements and estimation of benefits.
Mobility and reliability for larger areas of analysis, such as
2.10 The Right Measure
long roadway sections and corridors can be quantified with
for the Analysis Area
some individual statistics if the roadways are of the same type.
Exhibit 2.6 summarizes the mobility and reliability meas- But if freeways, streets, and/or other travel modes are in-
ures that should be used for several types of analyses and for cluded, cumulative statistics, TTI, and BI are very appropri-
different size areas or modal combinations (6, 1). Individual ate. Index statistics become useful at this higher level of analy-
traveler measures such as travel rate and the TTI are very use- sis when multiple roadways and large numerical values (e.g.,
ful for analysis up to the corridor level. At higher levels of statistics expressed in thousands or millions of hours) make
analysis, magnitude statistics such as delay and accessibility interpretation of relative conditions difficult.
also are useful. Examples of the application of these measures
to situations based on the level of analysis are included in the
2.11 The Right Measure
following sections.
for the Type of Analysis
Most mobility and reliability studies should be conducted at
geographic areas higher than individual locations and short sec- The recommended uses in Exhibit 2.7 are another illustra-
tions of roadway. At relatively small areas, the studies will typi- tion of how the mobility and reliability measures vary by the
cally be limited to near-term analysis of operational improve- scope of the analysis, but not by mode or facility included in
Mobility and Reliability Measures
Annual Delay
Buffer Index
Per Traveler
Travel-Time
Accessibility
Travel Time
Travel Rate
Total Delay
Congested
Congested
Congested
Percent of
Roadway
Travel
Travel
Index
Analysis Area
Individual Locations S S P P S
Short Road Sections P P S P P S
Long Road Sections,
S S P P S
Transit Routes or Trips
Corridors S S P P P S
Subareas S P P P P P P P P
Regional Networks S P P P P P P P P
Multimodal Analyses S P P P P P
P = Primary measure, and S = Secondary measure.
Note: Measures with delay components can be calculated relative to free-flow or posted speed conditions.
Exhibit 2.6. Recommended mobility and reliability measures for analysis levels (1).
