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The Signal | Jan/Feb 2017
Safer Roads Save Lives
Adding The Calibrator to Your Toolbox:
New Safety Analysis Tool Helps States Determine What’s a Good Fit
A new predictive analysis tool called The Calibrator helps
transportation professionals incorporate safety performance into
highway investment decisions.
Predictive analysis tools use crash, roadway and traffic volume data
to identify sites with the greatest potential for safety improvements.
The Federal Highway Administration (FHWA) recommends
predictive analysis as part of its Every Day Counts approach to
data-driven safety analysis, which focuses on strategies to target
investments with more confidence and reduce severe crashes.
An FHWA webinar recorded in November 2016 demonstrated how
to use The Calibrator, a spreadsheet-based tool to assess the
compatibility and applicability of safety performance functions
(SPFs) and crash modification factors (CMFs). SPFs and CMFs are
integral parts of the American Association of State Highway and
Transportation Officials’ Highway Safety Manual methods for
estimating the expected number of crashes for a roadway site.
SPFs—equations used to predict crash frequency—and CMFs—
factors used to compute the expected number of crashes after
applying a safety countermeasure at a site—are developed using
data from specific locations and times, so they may not apply to
other places or times.
“Conditions change over time and vary from state to state and even
within states,” Frank Gross, highway safety engineer for VHB, told
webinar participants. “It’s necessary to calibrate SPFs to ensure they
reflect local and temporal conditions.”
Calibration addresses variations in such factors as crash reporting,
road maintenance practices, weather, terrain and driver populations
and behavior. The webinar covered how to use The Calibrator to
calibrate SPFs and evaluate single and alternative SPFs using
techniques, such as goodness-of-fit measures and assessment tables.
Kentucky’s experience
The Kentucky Transportation Cabinet, which has developed
state-specific SPFs for about four years, started using The
Calibrator after learning about it at the 2016 Transportation
Research Board Annual Meeting.
“We were looking for tools to improve our SPF development,” said
Eric Green, research engineer at the Kentucky Transportation
Research Center. “We were starting to bump into questions about
how well these SPFs were fitting the data. The Calibrator is giving
us the tools to do these evaluations.”
Kentucky also used The Calibrator in a research project to examine
the effect of the length of a road segment on SPF development. The
Calibrator helped researchers compare SPFs created from 16
segments using the same roadway network and crash data, but
varying segment lengths of 0.1 mile to 5 miles.
“For the scenario we looked at, the recommended length is about 0.7
mile,” said Green. “Five miles was way too long, and 0.1 mile was a
little too short. This is in the context of rural parkways in Kentucky,
which are divided roads like interstates. We’re looking now at doing
the same analysis for different attributes of a roadway.”
For more information about data-driven
safety analysis, to view the “SPF Calibration
and Evaluation” webinar (part of the FHWA’s
how-to series on data-driven safety analysis)
and to download The Calibrator, visit www.
fhwa.dot.gov/innovation/everydaycounts.
ATSSA’s New Booklet Focuses on Member Opportunities with Emergence
of Connected and Automated Vehicles
“ATSSA Member Business Opportunities Related to Connected and Automated Vehicles,” ATSSA’s new, comprehensive booklet,
focuses on emerging technologies—connected and automated vehicles (CV/AV)—and how they’ll affect the roadway industry and
ATSSA member businesses. The booklet is the result of a study conducted by ATSSA and Alabama’s Auburn University.
The booklet explains the basic components of CV/AV technologies; CV/AV deployment plans throughout the country; the impact
of the technologies on ATSSA members; and recommendations on how ATSSA members can navigate their businesses with these
new technologies.
“ATSSA wants to ensure its members are on the cutting-edge of these newly emerging technologies,” said ATSSA Vice President of
Member Services Donna Clark. “Because ATSSA is committed to providing its membership with knowledge to be at the forefront of
the roadway industry, the association commissioned Auburn University to conduct the research last April. With the rapid pace of these
technologies, ATSSA believes its members should be educated on how the innovations might affect the way they do business.”
The publication will be mailed to ATSSA members on Feb. 15, 2017.