Highway Safety Barrier System
Will Cut Accident Rates
In hopes of reducing the number of
cross-over accidents on a busy segment of expressway in Oklahoma City,
ODOT has installed a wire cable barrier system of a design that has
never been used in the United States.
by Jeff Griffin, Contributing Editor
The four-strand Brifen Safety Fence is manufactured in
the United Kingdom by South Yorkshire-based Bridon Ropes, Ltd.
The new safety barrier consists of 3,333 posts which
support 140,424 feet of cable, says Carrie Clear, Oklahoma Department of
Transportation spokesperson. Posts are 52-inches long with 16.5 inches
buried in the ground. Ten and one-half feet separate the posts, which
support the four strands of tensioned cable, each composed of 21 wires.
Construction began in April and was completed the last
week of July. Total cost for system components and installation was
approximately $1.3 million, $10 million less than the amount required to
install concrete barriers. The contractor was Midstate Traffic Control,
Inc., Oklahoma City.
The system is designed so that the energy of a vehicle
striking the barrier is absorbed by posts and wire cables, with posts
bending or collapsing on impact. After a vehicle strikes the barrier, it
is guided along the fence as it slows to a stop. Damaged posts are pulled
from their sockets and replaced with new ones.
The barrier was installed adjacent to the southbound
lane of a seven-mile stretch of State Highway 74, also known as the Lake
Hefner Parkway. The expressway connects an east-west turnpike and
Interstate 44. North- and south-bound traffic lanes are separated by a
grass median. Since 1999, four cross-over accidents have resulted in six
fatalities and seven injuries.
Choosing the system
The Oklahoma DOT studied a variety of options, including
concrete barriers and an American-made three-cable barrier.
The U.K. product is significantly different from the
three-strand wire barrier systems used on some highways in the United
States. Department research, Clear says, indicated that the Brifen system
would be more effective than other designs.
“The Brifen system,” says Clear, “is installed
with greater line tensions than other cable systems, which means that
significantly fewer deflections occur on impact, reducing the seriousness
of accidents. Compared to the three-cable system, vehicles that strike the
barrier suffer less damage and their occupants have a lower risk of
Tests also indicated the system will perform better from
a maintenance standpoint.
“While the Brifen barrier costs a little more to
install,” says Clear, “it is less expensive to maintain.”
Clear says readjusting cables of other barrier systems
is a time-consuming and costly part of their maintenance. Brifen cables
are tensioned by the manufacturer before installation, eliminating
stretching during installation and subsequent readjustments.
The Brifen safety fence, she continues, is easier to
repair, and after minor hits, typically returns to its original alignment
and retains the capacity to withstand additional strikes before repairs
ODOT also found that the system is easier to dismantle
to make emergency cross-over points.
“The highway where the cable has been installed is
very accessible,” says Clear. “With entry and exit ramps every mile,
we do not anticipate it will be necessary, there are joints every 500 feet
with tensioning screws that can be easily removed. Emergency personnel
then pull several posts from their sockets, and vehicles drive across the
Before making the decision on which barrier to use, ODOT
installed a 1,000-foot test section late last year so that researchers
could observe construction, appearance, and maintenance of the system. In
December, the test section prevented at least two cross-over collisions,
Finally, ODOT liked the looks of the system.
“Brifen steel posts are smaller than the wooden poles
used in the U.S. system,” says Clear, “allowing them to blend with the
Bridon Ropes, Ltd. says the four-cable barrier evolved
from an original two-strand design based on cable systems used on aircraft
carriers to restrain landing planes. The firm’s highway safety fences
are used in 30 countries throughout the world.
Jeff Griffin is a freelance writer
specializing in the construction industry.
Reprinted from Better Roads Magazine