Stopping or turning a motor vehicle is a function of basic physics: mass, velocity, momentum, friction, and reaction time. Accidents increase when drivers ignore safe driving guidelines.

When it is slippery, you need a greater stopping distance and you are less likely to go where you want when turning. Tailgating causes accidents.

4 Wheel Drive can still slip. Four wheel drives can increase safety directing power to the wheel(s) with traction. However, you can still slip and slide if not careful.

Don't Drive too Close: What will you do if the vehicle in front of you hits something and stops? Keep a good distance away from the car in front of you. A safe distance depends on your speed and other factors.

Tire grip is limited on slick surfaces. Try to separate acceleration and turing to maintain wheel traction. Gradual turns are easier than sharp turning.

Slow down well before a turn. Too fast, and you may not make that turn and slide into something. Trying to turn and slow simultaneously can exceed tire grip.

Mass: the heavier you are, the more there is to stop

Velocity: speed affects stopping distance as well as what it takes your tires to change the vehicle's direction when turning.

Momentum: mass tends to keep moving in the same direction. The tendency to keep moving is a function of Mass x Velocity. The heavier you are and the faster you are moving, the more you are likely to keep going and not stop or not turn.

Stopping Distances: To change the speed is a function of Mass x Velocity x Velocity. This means to stop is a function of mass and the square of velocity. View a graphic example of how speed affects stopping distance. This means that if you double the speed from 10 miles per hour to 20 miles per hour, it takes four times the distance to stop. Triple the speed and it takes nine times the distance to stop. Heavier vehicles take greater distances to stop. Giving the same braking braking systems, double the weight, and it takes twice the distance to stop. Learn about the Physics of Auto Stopping Distances.

Reaction Time: Stopping also involves your reaction time. How quick can you react? The faster you travel, the greater the distance you need to stop. Click here to see a demonstration about reaction time and stopping a motor vehicle. Cell phones, distractions, fog and blinding snow can slow reaction time.

Friction / Tire Grip: To start, stop, or change direction, friction is needed. Tires must grip the road surface to change Momentum (start, stop or turn). Friction is a function of the tires, weight, and road surface they are trying to grip. Tire characteristics like size, width, tread quality, number, tire studs, chains, and inflation are factors. Once tire grip is broken, the wheels no longer hold the road and changing direction, slowing, or speeding are overcome by momentum.

Drawing of one of Dr. Bermant's young patients after a car accident resulting in a forehead laceration.

Speed Limits: Posted speed limits are for normal driving conditions. Such speeds can be dangerous when slippery or when visibility is impaired.

Stopping and turning ability depend on the road surface.

Newly wet roads: Wet concrete is more slippery than dry. Shortly after it rains, oils on the road surface tend to float on water. A new rain can lift oils from the road that can make it slippery when wet.

Ice: Ice is slippery. Tires just do not grab ice like they do asphalt. Wet ice or snow covered ice are worse for friction.

Black Ice: is a little darker and dull looking and almost invisible on a road, often from snow melting and re-freezing. Since it is hard to see, drivers miss it and accidents are common. Most commonly found when temperatures are near or just below freezing.

Differential Freezing: Some parts of a road may be frozen before others. Bridge driving surfaces can freeze before pavement on firm ground. Some parts of the road may have more or less salt changing the freezing temperature. What may be unfrozen under the sun, may be ice in the shade.