Science Behind Travel Troubles

Ominous weather across the country means many Americans may be suffering through long, white-knuckle days of traveling this holiday season. And, while there's little to be done about traffic or the weather, at least you can think about the science behind it.

In recent years, researchers have searched for explanations behind common traveling hazards and annoyances from slippery roads to bumper-to-bumper traffic to flight-delaying weather. Below is a summary of some of their findings.

Slippery When Wet

Most drivers have experienced skidding out of control when it's raining and the pavement is wet. The cause may seem obvious, but, in fact, physicists have been debating for years what could be the main cause behind the problem.

This November, a team of scientists offered their theory in the journal "Nature Materials," to explain how even a drizzling rain can cause a 25 percent reduction in friction between tire and road at speeds below 40 mph. They discounted molecular attraction between atoms within the pavement and the tire's rubber since they calculated only 1 percent of a tire touches the pavement at a given time, thanks to the curvature of the wheel and the rough surface of the road.

Instead, Erio Tosatti of the International Center for Theoretical Physics and his colleagues determined the biggest factor was the way water pools within the tiny valleys of road pavement's rough surface. The effect is a smoother surface, which reduces how much the tire's surface is deformed upon contact. The less deformity of the tire's surface, the less friction. And friction is what keeps the driver in control.

In heavier rains, drivers can experience the more dramatic effect of hydroplaning. According to the National Safety Council, hydroplaning happens as water on the road builds up in front of a car's tires faster than the car's weight pushes it away. The water pressure then lifts the car up and causes it to slide on the layer of water between the car's tires and the road.

To avoid either problem, drivers are advised to make sure their tires' treads are in good shape and inflated properly and when rain falls, to slow down and try to avoid large puddles.

Stuck in Traffic

After crawling along a packed roadway at a snail's pace for hours, nothing about traffic may seem to make sense. But, in fact, scientists have found there are a few constant variables when it comes to congestion: flow, speed and density.

As you might expect, greater traffic density usually leads to slower overall speeds. And the better the flow, the less likely cars will interfere with each other and speeds increase. But what may not seem so obvious is at some point traffic flow can improve with density.

According to studies by Bernardo Huberman at the Xerox Palo Alto Research Center and Dirk Helbing at the University of Stuttgart, Germany, there is a unique point at which more cars on the road can improve congestion. This is when, as Huberman explains, traffic begins to move as a single solid mass, rather than as separate, fluid-like entities.

When all lanes of a highway are filled, traffic can still move along at a fairly steady clip as long as large enough gaps remain between cars. Lead-foot drivers may find driving in such a solid flow frustrating, but Huberman says the constant speeds in the lanes actually makes for a more efficient pattern than when cars are slowing and speeding around each other in random patterns.

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