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!
|The numbers are staggering:|
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.
- There are 3.9 million miles of road in the U.S.
- There are 45,000 miles of interstate highway.
- Over $1 trillion has been invested in highways and bridges in the U.S.
- Over 2.7 trillion miles are traveled each year on U.S. roads - that's four times the level of 1960.
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:
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.
- Relatively low cost.
- Quick application processes using continuous paving machines.
- Long wear.
- Smooth surfaces for less tire and vehicle wear.
- Low noise.
- Good anti-skid characteristics.
Some additional recycled materials that are being examined for use in asphalt include:
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.
- Fly ash
- Reclaimed asphalt paving
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.