Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
The following information was obtained in an effort to summarize the current activities by public
agency programs and private entity sources regarding travel time reliability:
Washington State DOT (WSDOT)
The Gray Notebook is WSDOT’s main performance assessment, reporting, and communication
tool. The Gray Notebook (http://www.wsdot.wa.gov/accountability/default.htm) provides quarterly, in-depth reports
on agency and transportation system performance. The purpose of the Gray Notebook is to keep
WSDOT accountable to the Governor, the Legislature, Washington State citizens, and
transportation organizations.
Included in the Gray Notebook is the Performance Dashboard, which is an overview of the key
performance indicators for each of the policy goals. The Performance Dashboard shows the current
and previous performance mark for each measure. It indicates which way the program is trending,
and why. Five policy goals/performance measures are included in the Performance Dashboard:
safety, preservation, mobility/ congestion relief, environment, and stewardship. The only measures
related to travel time reliability are included under the mobility/congestion relief policy goal as
follows:
• Average Clearance time (in minutes) for major (90+ minute) incidents on key Puget
Sound corridors; and
• Annual weekday hours of delay statewide on highways compared to maximum
throughput (51 MPH) in thousand hours.
Georgia Regional Transportation Authority (GRTA)
The Georgia Regional Transportation Authority (GRTA) produces an annual report, titled the
Transportation Metropolitan Atlanta Performance (MAP) Report, which reports on the region’s
progress toward improving Mobility, Transit Accessibility, Air Quality, and Safety.
Included in the Transportation MAP Report are the following mobility measures to track highway
mobility:
• Freeway Travel Time Index – The Travel Time Index (TTI) is the ratio of the average
travel time over the free-flow travel time obtained for a certain portion or segment of
the freeway system. For this report, measurements were created using GDOTs
NaviGator video detection cameras.
• Freeway Planning Time Index - Two travel time reliability measures are reported:
the planning time index (PTI) and the buffer time index (BTI). Measurements for the
planning time index were created using GDOTs NaviGator video detection cameras,
similar to the freeway travel time index.
o PTI is the ratio of the 95 th percentile travel time, also known as planning time, over
the free-flow travel time obtained for a certain portion or segment of the freeway
system. In other words, PTI tells a traveler how much longer it is going to take to
make a trip under congested conditions compared to free-flow conditions - so that
the traveler arrives on-time 95 percent of the time.
o BTI is defined as the difference between the 95 th percentile travel and the average
travel time. BTI is the size of the buffer time expressed as a percentage of the
average travel time and obtained for a segment of the freeway system. In other
words, BTI tells a traveler the extra time as a percentage of the average travel time
RELIABILITY PERFORMANCE MEASURES AVAILABLE TO AGENCIES Page A-3