WASHINGTON, Dec. 28, 2015 – The holiday season is a time of mass transit. This year warm temperatures helped travelers arrive at their holiday destinations in a safe and timely manner. Unfortunately, severe winter weather throughout much of the country is expected to usher in 2016.
With winter weather back in the forecast, it is important that drivers refresh their winter weather driving knowledge, especially those who live in climates that rarely see snow.
In that spirit, drivers can benefit from a better understanding of what happens when their vehicles encounter slippery road conditions.
A physicist might start such an explanation by modeling a vehicle as a simple cube with wheels that experience rolling friction.
This cube would encounter varying friction as it travels along a road. This variation in friction would, in turn, slow the vehicle, thereby requiring the driver to periodically accelerate and decelerate.
When encountering an uneven change in the surface of the road, one side of the cube would accelerate differently from the other side. The vehicle would be pulled to one side of the road.
Furthermore, it is helpful to recognize that a vehicle is essentially a dumbbell-shaped object where the two sets of tires are joined together by a “bar,” i.e., the car body. As such, the vehicle can also be modeled after a dumbbell-shaped object to help explain what is happening when the car is turning.
If a driver wants to speed up or slow down, he or she pushes on a pedal to add or subtract rotational force, a.k.a. torque, to the tires. With this torque comes another “force” that “pushes” the vehicle left when the car is accelerating and right when the vehicle is decelerating.
When the tire surface is flattened against the road, the rubbing of the tire against the road creates friction. The rotating surface of the tires encounters rolling friction from the road, which causes the vehicle to slow, while sliding friction helps the vehicle stay in the middle of the road. Sliding friction is what prevents a tire from sliding right or left.
For those who live in areas where winter weather is common, a high quality set of snow tires should be considered a necessity as they boost sliding, as well as rolling, friction.
By the driver’s adding or subtracting torque via the brakes and gas pedal, the “pushing force” of the torque on the tires can become greater than the sliding friction of the road. If the road lacks enough sliding friction to keep the vehicle on the road, the dumbbell-shaped vehicle will start to slide and spin instead of going straight.
In other words, improper acceleration is what causes accidents when the roads are slippery.
As a change in direction is also a form of acceleration, curves and the act of steering can also cause a vehicle to slide. Going around a curve requires the driver to “accelerate” in order to avoid deceleration. The difficulty of maintaining a constant speed, i.e., not accelerating, when going around a curve is what makes driving on a slippery curve so dangerous. It is best to either accelerate or slow down before entering a curve. In winter weather, drivers must also be more conscious of how they turn their steering wheel and approach even the slightest of curves. Slow, well-controlled steering will help prevent a vehicle from slipping.
Meanwhile, going up a hill too slowly in the winter can also throw a vehicle off the road. Vehicles slow as they go up hills. In order to maintain a constant speed, drivers must add “extra torque to their tires,” i.e. hit the gas pedal and accelerate as those go up the hill; otherwise, the vehicle will decelerate and start to slide. It is, of course, best to slowly accelerate just before driving up an incline in order to avoid the need to accelerate while on the hill.
Consequently, driving on slippery roads requires a constant effort to consider how fast the vehicle is accelerating. Driving safely in winter weather, therefore, means being aware of how quickly one accelerates. Drivers also need to go slower in slippery road conditions because it gives them more time to properly accelerate.