How Road Design Affects Your Winter Driving

Plus: Top Cold-Weather Tire Tips

By Rod O'Connor

When you’re driving smoothly along a snow-dappled highway in a toasty-warm car, it’s often easy to forget that a lot of work goes into making roads safe in all weather conditions. Here Tom Yager, a senior research engineer at NASA Langley Research Center, shares the science behind highway design, explains the performance differences between asphalt and concrete, and reveals his top tire maintenance tips to help you get a grip this winter driving season.

Making Groovy Roads
If roads lack proper drainage, water can build up, causing vehicles to hydroplane or—if temperatures are frigid and puddles turn to ice—slide off the road. But with the proper grooves on the pavement’s surface and slopes along the edges, precipitation can safely drain away before you even really notice it under your tires.

Department of Transportation employees use a few different techniques to add the grooved texture to road surfaces, Yager says. One is called “longitudinal tining,” in which the road workers use a rake to create shallow channels in wet concrete in the direction of traffic flow. In another technique, “diamond grooving,” workers use diamond-tipped saw blades to cut quarter-inch slices into the pavement to increase friction at the point where the rubber hits the road. “It produces a corduroy-like effect,” Yager explains. “These small ridges and valleys promote the removal of water between the tire and the surface of the pavement.”

In either case, the grooves are placed about 1 to 1½ inches apart, because at any given time, only about a foot of a car’s tire surface touches the road surface. Closely spacing the grooves means more drainage and better traction in that small area. “In wet conditions, grooved surfaces can restore friction performance to pavement surfaces and extend their service lifetime by five to 10 years,” Yager says.

Concrete vs. Asphalt—Which Is Better?
Whether you’re cruising across the country or taking your kids to school, most of the road surfaces you travel on every day are built from one of two pavement types: concrete or asphalt. Concrete, a poured mixture of cement paste and water, is considered a rigid pavement. Hot mix asphalt, which uses an oil binder and must be rolled onto a surface, is more flexible.

So how do the two types match up when it comes to winter driving? According to Yager, asphalt can be prone to “rutting,” which are indentions in the wheel paths of the pavement. Heavy trucks, moisture and temperature changes all contribute to this deterioration in asphalt. And when heavy rain or melting snow enters the picture, these ruts can generate a river of water running right in the path of your tires. In contrast, concrete’s inherently rugged ingredients (such as limestone and rock), combined with the reinforcing steel rods (or rebars) that serve as a framework for the poured concrete, provide a rigidity that counteracts rutting. “On roads with the same traffic volume in the same climate, concrete will last longer than asphalt,” Yager says.

Asphalt, however, has some key advantages: ease of maintenance and overall lower costs. Anyone living in a cold climate has likely witnessed speedy winter pothole crews rolling out asphalt to patch up roads that once resembled the surface of the moon. “Asphalt roads can be restored faster,” says Yager.

In terms of noise, proponents of each side claim their material is quieter. Yager, for his part, believes asphalt is louder because of its flexibility. “Concrete’s lack of flexing means less vibrations, which equals less noise,” he says.

Tire Tips
Even well-designed highways can be treacherous in winter. Snow, sleet and slush create a thin film of water between your tires and the pavement; and when temperatures are close to freezing, your tires lose their ability to maintain traction because the weight of your vehicle melts snow as you pass over it. (However, extreme cold can actually improve traction, because the snow and ice won’t melt as easily.) Regardless of the pavement surface you’re driving on, certain steps should be taken in early winter to help improve the adhesive friction of your vehicle’s tires—and therefore make you safer out on the road.

  • Check your tire pressure monthly. When tires have low pressure, their surface becomes less rigid. This causes the tire to make less contact with the pavement and become more prone to hydroplaning. The treads on severely under-inflated tires can actually become concave and trap water. If you’re unsure of the tire’s recommended PSI (pounds per square inch), take a peek at the label inside the driver-side door. Remember, cold reduces the pressure, and heat causes pressure to rise. So it’s important to check your tires when the car has been off for at least a half-hour.
  • Consider investing in winter tires—especially if you live in an area with serious snowfall. In low temperatures the shallow, rigid tread compounds of summer tires become even harder, almost plastic-like. Winter tires, on the other hand, use rubber compounds designed to stay soft and continue to grip at low temperatures, and their larger treads provide additional contact with the road, which helps you push through snow, ice, salt and other contaminants.
  • Replace worn-out tires. If your tires don’t have built-in wear indicators, here’s a tip for checking tread wear: Place a penny in the tread groove with Lincoln’s head upside down, facing out. If all of Lincoln’s head is visible, it is time to shop for some new tires. (This means the tread depth has gone below 2/32 inch.) Worn tires are particularly dangerous on wet winter roads, because the grooves aren’t deep enough to channel water out from beneath the tread. Need new tires? No problem. Read How to Pick the Right Tire for Your Vehicle (And Driving Condition).
  • Slow down. On slick and icy roads, cars can lose control even at low speeds. Still, Yager advises giving the lead foot a break when driving during the winter driving season. “Slowing down will always help you better negotiate the road in front of you,” he says.



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