Paving the way to safer driving
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 pretensioning seat belts, 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 United States.
- There are 45,000 miles of interstate highway.
- More than $1 trillion has been invested in highways and bridges in the U.S.
- More than 2.7 trillion miles are traveled each year on U.S. roads – that's four times the level in 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, however, asphalt is being used to pave over the original concrete surfaces. In fact, more than 90 percent of the nation's highways are now covered with asphalt pavement.
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.
- 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
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:
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
Hydroplaning: Channeling water
While the ideal paving material may be years away, highway engineers have come up with a partial solution to help your car resist hydroplaning. Remember: A mere quarter inch of water on the highway can induce hydroplaning in tires that results in a loss of vehicle control, especially at speeds above 55 mph. Even if your vehicle has new tires, traveling fast in the rain increases your likelihood of 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.
Absorbing highway barriers
Much of what we've covered so far can be considered "active" safety – road designs that help you avoid an accident in the first place. But accidents do still happen, and here, too, highway engineers have advanced the state of the art considerably since Eisenhower's day.
Concrete barriers alongside many highways are designed to direct a vehicle's path, preventing an out-of-control vehicle from crossing into the opposing lanes. The barriers help to maintain the original direction of travel. Plastic, water-filled hydrobarriers are placed in front of bridge abutments and other immovable objects. These barriers are engineered to perform in much the same way as the crumple zones in your vehicle – to absorb impact energy if a vehicle strikes it.
Even the way in which road signs are positioned and held in place has been closely examined in modern highway design. In the past, road signs and traffic lights were mounted on strong telephone poles or stout steel posts. Although they lasted a long time, these rigid signs presented a grave injury risk should a vehicle hit them. Today, many supporting poles and signposts are designed to break away upon impact. In this way, these signposts are much less likely to intrude into the passenger compartment during a collision, helping to protect the vehicle’s occupants.
Together, these new types of poles and barrier systems have saved countless lives and injuries as they redirect and absorb collision energy or simply break away.
A sign of the times
Another dramatic improvement is the information imparted to drivers from highway signs. The technology of today's road signs includes highly reflective sign materials, internationally standardized symbols, illuminated signs that are visible in bad weather or low light conditions, and variable-message signs that can supply different information to drivers depending upon weather, time of day or traffic conditions.
Of course, road signs aren't the only information found on America's roads. Advances have been made in the materials and application of the lines painted onto the road that help control and direct traffic flow. Keep in mind that road markings and reflectors must be durable enough to withstand being run over by millions of vehicles and tough enough to stand up to the scraping of snowplows, road salt and submersion on flooded highways. New epoxy-based paints, hot-applied thermoplastic tapes and polyester resins are finding their way onto more and more highways. The scuff- and dirt-resistance of these high-tech materials is especially clear at night, so drivers can easily distinguish between lanes and see the edges of the roadway more clearly.
Many more highways are also equipped with centerline reflectors that clearly delineate the lanes of travel. Called "Botts Dots," they are the brainchild of Elbert D. Botts, who in the 1950s invented a reflective raised "dot" and found a way to adhere it to the surface of the road. These raised "dots" provide a bump-bump-bump reminder if your vehicle crosses the center line and allow added visibility to see lane stripes at night, especially in rain or fog.
The road to the future
The road to increased highway safety never ends. As traffic levels continue to increase, engineers and researchers are finding new and innovative ways to keep it all flowing smoothly and safely.
The use of new paving materials that provide better wet-weather and winter grip is now under study. Traffic lights and variable speed limit signs that sense traffic flow patterns are becoming "smarter" by anticipating actions that will move traffic more smoothly. Experiments are taking place with in-car transmitters and receivers that communicate with the highway to provide the driver with more information than a road sign ever could. Some engineers are even predicting that the future will see cars that drive themselves to their destinations, once the driver has slotted onto a new kind of super-intelligent highway system. If it all sounds a bit futuristic and maybe even a little unnerving to those of us who like to drive, such drastic concepts may become a necessity in the not-too-distant future, as more and more cars and trucks hit the highways.