(dramatic music)
- [Narrator] Roadway designers use safety prediction models
to evaluate the effectiveness of roadway safety features.
The Texas Department of Transportation
with help from the Texas A&M Transportation Institute
recently refined these models
for use on roadways as wide
as 12 lanes or for freeway managed lanes.
Researchers also updated local calibration factors
in the models and developed an analysis tool to
help practitioners who use them.
- There's a document called the Highway Safety Manual
which contains models to estimate the crash frequency
that you would expect
for roadways of different types, and some
of the most recent material was getting a little old
maybe five, 10 years ago.
It was developed
and most importantly was developed using data
from other states.
So our goal here was to calibrate those models
to Texas conditions.
Looking specifically at urban freeways.
- So there are certain limitations
to the Highway Safety Manual
especially highway safety manual predictive method.
And these three limitation include
like maximum number of lanes, freeways with managed lanes,
the average interval traffic or AGT.
So Tex DOT has been developing major projects
where we have 10 plus lanes.
We have free lanes with managed lanes and also higher AGT.
So it would be logical to develop new models where
we address the Highway Safety Manual limitation
as well as calibrate these models to the Texas condition.
- Specifically, there is interest
in estimating crash frequency
on urban freeways with managed lanes,
high occupancy vehicle lanes, toll lanes, et cetera.
That required us to collect data
for segments on these types of roadways in Texas.
In the case of managed lanes
that meant developing new models and
for just conventional urban freeways, we had to
compare what the Highway Safety Manual was predicting
for crash frequency and what we were actually observing
in our sample of segments.
One of the key things we did in this project
was we developed a spreadsheet program where
the analyst can just enter the input data to
describe the facility that they're evaluating
the traffic volume, the number of lanes,
the cross sectional widths, the presence of ramps
and so forth.
That makes it easier
for them to apply the Highway Safety Manual
without having to do it the hard way
with a calculator and working through the equations by hand.
- The findings from this study, you know
will be used by Tex DOT designer to develop a safer design
and provide more reliable information to decision makers
and hopefully the findings will enhance the knowledge
and fill the gaps in the knowledge
and improve the knowledge to improve the infrastructure
not only within Texas, but also across the United States.
- [Narrator] For more information
and to find the publications for this project,
please visit the Tex DOT research library
at the link shown below.