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 |  |  | | | | Paving the Way to Progress | | By Kevin Clemens | |
You're driving down the highway in a modern automobile – a marvel of safety
engineering. Your car has anti-lock brakes and dynamic stability control to
help you avoid an accident, plus pre-tensioning seatbelts, front and side
airbags SRS, and engineered crumple zones in the chassis to help you survive
an impact. But zipping under your all-season tires at 95 feet per second is
another modern engineering marvel – the pavement itself!
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The numbers are staggering:
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There are 3.9 million miles of road in the U.S.
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There are 45,000 miles of interstate highway.
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Over $1 trillion has been invested in highways and bridges in the U.S.
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Over 2.7 trillion miles are traveled each year on U.S. roads - that's four
times the level of 1960.
But when President Eisenhower signed the Federal Highway Act in 1956, and
construction began on the concrete ribbons of interstate highways, even the
most visionary engineer could not have imagined the advancements we take for
granted today in our highways. From anti-skid pavement surfaces to water
drainage controls, from driver information signals to scientifically designed
crash barriers, America's highways are now engineered to promote much safer
travel for cars and heavy trucks.
Where the Tires Meet the Road
Initially, much of the nation's roadways were made from concrete, which is a
mixture of cement, sand and crushed rock. More and more today, however,
asphalt is being used to pave over the original concrete surfaces. In fact
over 90 percent of the nation's highways are now covered with asphalt.
Asphalt is made from a tar-like substance that is separated from crude
petroleum and then mixed with aggregates like sand, gravel and crushed stone.
Modern paving machines apply asphalt in a hot layer, which is then rolled to a
very smooth road surface.
Some of asphalt's advantages are:
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Relatively low cost.
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Quick application processes using continuous paving machines.
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Long wear.
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Smooth surfaces for less tire and vehicle wear.
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Low noise.
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Good anti-skid characteristics.
The last point, of course, is important for traffic safety. Because asphalt
can accept a reasonably high percentage of recycled materials within its
makeup, engineers have looked to materials that can help increase traction
without adversely affecting other important characteristics, such as noise or
tire wear. The ideal solution also includes the use of recycled materials in
the asphalt mix...and that's just what engineers have come up with in today's
modern paving materials. Recycled rubber from tires added to the asphalt mix,
for example, yields measurable improvements in traction and reductions in
noise levels compared to ordinary asphalt.
Some additional recycled materials that are being examined for use in asphalt
include:
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Fly ash
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Plastics
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Reclaimed asphalt paving
Increased levels of wet-weather traction are constantly being sought, and new
paving materials are being developed today that may add even more safety to
wet-weather driving.
Channeling Water
While the ideal paving material may be years away, highway engineers have come
up with a partial solution today to help your car resist hydroplaning.
Remember: A mere quarter inch of water on the highway can induce hydroplaning
in tires, especially at speeds above 55 mph, resulting in a loss of vehicle
control. Even if your vehicle has new tires, the faster you travel in the
rain, the more likely it is that you will experience hydroplaning.
You've probably noticed that many highways now have surfaces designed to
provide proper drainage during heavy rainstorms. Narrow, longitudinal grooves
ground into the road surface help break up the film of water that can form
under a hydroplaning tire. Of course, this grooved pavement is not a cure-all.
When driving over rain-covered roadways, the best way to avoid hydroplaning is
to slow down.
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