Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Table B.3 - Summary of Disruption Data Characteristics by Type of Disruption
Disruption Type Data Collected Source Availability Location
Traffic Incidents
Weather
Accident Data
Statistics on the nature (size, severity,
duration) of the accident;
Disruption of roadway operations (the
number of lanes closed);
Response after accident; and
Data on traffic incidents (stalled or
disabled vehicles, debris).
Basic Weather data
DOTs
State Database Archives
Private Sector
Traffic.com
TMC operators and
Freeway Service Patrols
Traditional crash data
Specific Incident Response
programs
National Climatic Data
Center (NCDC) of the
National Oceanic and
Atmospheric
Administration (NOAA)
Major Urban or
Tourist Areas
Area-wide
Work Zones/
Construction
Planned Construction activity (number of
lanes closed, period of time)
DOTs
State Database
Urban/Rural
Fluctuations in
Demand/Special Events
Signal Timing
Bottlenecks/In adequate
Base Capacity
For a Large Event: Time & Date, Nature
of the changes in traffic demand.
For Other Events: No Data Collected
Traffic Control plans (signal cycles,
phase length, order, signal offsets, and
base ramp metering)
Public or Private Sector
Traffic Management Plans
Operating traffic agencies
Urban Areas
Usually Available
Specific Timing Plans implemented Operating traffic agencies Rarely available
Phase length actually operated
Operating traffic agencies
Almost Never
implemented
Change in geometry (lane drops)
Traffic patterns (weave/merge sections)
Good data
Visual Disruptions (Sightseeing, All Roadway Agencies
Rubbernecking)
No record
Minor changes in functional capacity
Potentially
Strategies for improving travel-time reliability may focus on a specific cause or address multiple
sources of unreliability. Determining the various sources of unreliability using disruption data may
then aid in determining the potential strategies to be implemented.
Monetizing the Certainty-Equivalent Values
Since the certainty-equivalent values of an option can be expressed in minutes or hours of delay,
unreliability can be monetized by applying the appropriate values of time to these delay measures.
Measuring unreliability in future periods permits the analyst to determine the present discounted
value of unreliability and to evaluate long-term network improvements or management policies
that are directed at addressing unreliability.
Similar to other parameters of the options approach, certainty-equivalent values should be selected
to measure what is important to the reliability issue being addressed. For example, if a study is
focused on improving the reliability of freight movement, the analyst may only be interested in a
strategy's effect on the certainty-equivalent delay that is experienced by trucks. In this case, only
the value of time for truck travel might be used to monetize the value of unreliability. In general,
DETERMINING THE ECONOMIC BENEFITS OF IMPROVING TRAVEL-TIME RELIABILITY Page B-17