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The
Humpback Bridge
and
Other Virginia Crossings
Down
in Alleghany County, just west of Covington, stands
a structure unique in the U.S. -- the Humpback
Covered Bridge. Built in 1857, it is so-named
because the bridge is about four feet taller in the
middle than at either end and is the only design of
its type in the country. The extra height, as well
as the decking, was designed to protect it from
flooding and help it last longer.
Bridges
were covered to protect the truss, the
interconnected side timbers of wooden bridges, not
the flooring, as many believe because the truss was
the most expensive part of the structure. An
unprotected bridge would last only 10 years, but
covered, it could last for centuries barring natural
or manmade disasters.
At
one time there were hundreds of covered bridges in
the commonwealth, but fire and flood took their
toll. By 1900, metal had replaced timber as the
material of choice, and was soon superseded by
reinforced concrete in the early 20th century.
Today,
the Virginia Department of Transportation lists eight
surviving covered bridges in the Old Dominion.
In addition to the Humpback structure that spans the
James River, there is Meem's
Bottom Bridge over the North Fork of the
Shenandoah River in Shenandoah County; the
Bob White Bridge and the
Jack's Creek Bridge over the Smith River in
Patrick County; and the Sinking Creek Bridge on Sinking Creek in Giles County.
Three other decked bridges – one in Rockingham
County and two in Giles County -- sit on private
property.
Wooden,
roofed bridges aren’t the only spans of historical
interest in the state. Back in 2000, VDOT published
“A
Survey of Masonry and Concrete Arch Bridges in
Virginia” to determine which stone bridges
were eligible for preservation with the National
Register of Historic Places.
In
the early years of the commonwealth, stone bridges
were not built as often as wooden bridges. Masonry
structures were expensive and required a certain
engineering skill. Also, the sources for stone and
mortar weren’t always available.
The
VDOT study identified 21 of 127 masonry arched
bridges as eligible for the National Register of
Historic Places list. Nine were built before 1900
and served as canal, turnpike and railroad bridges.
You can see an example of a turnpike bridge, built
circa 1823, in the Falling Creek Wayside Park in
Chesterfield County.
A
number of the early 20th-century masonry bridges are
the work of civil engineer Daniel Luten, who by 1927
had received 50 patents for reinforced-concrete
designs related to bridges. His goal: to reduce
cost, without reducing strength. A typical Luten
bridge – more than 10,000 were built according to
his designs from 1900-1932 in the U.S. -- is found
crossing the Dan River on Route 29 in Danville.
Arched
masonry bridges became less popular in the heyday of
road and bridge construction in the 1940s and 1950s,
when design standardization was the goal. Today,
there are more than 21,000 bridges in Virginia.
Among the most noteworthy are the 23-mile Chesapeake
Bay Bridge Tunnel, which connects Virginia Beach
to Cape Charles, and the 4.6-mile Monitor-Merrimac
Memorial Bridge-Tunnel, which crosses I-664 in
Hampton Roads. The latter opened in 1992 and 3.2
miles are a double trestle bridge.
Virginia’s
tallest bridge is the recently constructed
175-foot-high Wilson Creek Bridge, also known as the
Smart Road Bridge. The
Smart Road is a short, limited-access road in
Montgomery County maintained by the Virginia Tech
Transportation Institute and used to test
transportation technologies. Power and communication
lines run its length, equipping it for research.
Engineers
are not the only people studying bridges. It seems
the Old Dominion’s spans are habitat for creatures
great and small. Wildlife biologists with the
Virginia Department of Game and Inland Fisheries
have launched a "Wildlife
and Bridges" project to document the birds,
mammals and even a reptile or two that call the
state’s bridges home. So far, they have found
seven species of birds, eight species of mammals and
one reptile. Among the birds are various types of
swallows, osprey and peregrine falcons. The mammals
include six species of bats, woodrats and gray fox.
A black snake feeding on a bat was the lone reptile
the researchers found.
Biologists
believe many species are opportunistic and when
natural habitat is destroyed due to flooding,
overgrowth or man-made development, various bridge
structures offer alternative housing. Tall bridges
provide niches for swallows; small bridges with
I-beams create a ledge for phoebes to nest; or the
expansion joints in an overpass provide a tight
crevice for bats raising their young.
The
density of wildlife living on the commonwealth’s
bridges varies according to geographic region. The
Piedmont Region, in the center of the state, boasts
the most occupants. Fifty percent of bridges in that
area host five species of birds, three species of
mammals and that lone reptile. The mountain regions
come in next with 34.4 percent of their bridges
occupied. The coastal plain, which stretches along
the Atlantic and extends 100 miles inland is the
least attractive to wild creatures. Only 18.4
percent of its bridges host wildlife.
It
seems Virginia’s high technology, as well as its
fauna can co-exist. Who knows what creatures will
soon grace the Smart Road Bridge?
Next:
Grave Matters: Cemeteries in Virginia
--
May 30, 2006
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