Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
• Number of VMS signs in place
• Number of calls to a 511 system
• Number of events incident management systems responded to last month
• Average duration of an incident management system response
Outcome Measures
Output measures do not report on the effect those agency actions have on overall changes in travel
time or delay. Performance measures that report these conditions and that are more-readily
applicable to understanding travel-time reliability are commonly called “outcome” measures.
Where roadway agencies have begun reporting outcome measures, the most commonly reported
measures are the following:
• Total volume served
• Truck volumes served
• Mean travel time experienced
• Buffer Index
• Planning Time Index
• Travel-time Index
• On-time percentage
Current Performance Measures for Freight Movers
Many states are moving forward with developing roadway performance measures specifically
targeted for freight. The truck-oriented freight performance measures most frequently used by
states are roadway-based volume or usage statistics such as truck miles traveled, trucking tonnage
carried on the roadway, and route miles usable by trucks. Such information is based on roadway
inventories, vehicles volumes, and vehicle classification counts that many transportation agencies
already collect for a range of other planning and engineering reasons. Because of a lack of data,
route-related measures, such as origin-destination patterns travel-route information, and other
factors that involve a truck’s entire trip on the transportation network, are not often used. Many
state agencies agree with the usefulness of measuring the reliability of freight deliveries but do not
have the data to do it accurately. Several states are actively exploring ways to collect the data
necessary to report on freight-delivery reliability. While these programs are not yet fully
operational, the measures being explored are discussed below.
One idea is that reliability could be measured as a statistical index derived from travel time, which
could be a product of GPS data obtained from actual truck movements. Several roadway agencies
suggest that the portion of trucks arriving on time is the best indicator of the reliability of a
highway system from the freight mover’s perspective. It was also suggested that the statistic “one
standard deviation above an average travel time” could also serve this purpose. This measure is
useful and easy to understand. However, it was noted that one major issue in implementing either
of these measures is reluctance on the part of carriers to share information with governments.
Several of the more-detailed efforts to analyze or develop freight performance measures (New
Jersey, Minnesota, and Texas) have stressed the need to have measures that are directly applicable
within their organization’s institutional framework. In other words, the measures should be able to
inform alternative approaches regarding how a state fosters freight mobility.
ISSUES AFFECTING THE EFFECTIVENESS OF AGENCIES
States that are actively looking to report more travel-time reliability performance measures have
described a number of concerns about their ability to develop and report reliability-related
EFFECTIVENESS OF AGENCIES Page 14