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2.6.2 – Matching Speed to the Road Surface
You cannot steer or brake a vehicle unless you have traction. Traction is friction between the tires and the road. There are some road conditions that reduce traction and call for lower speeds.
Slippery Surfaces. It will take longer to stop and be harder to turn without skidding when the road is slippery. Wet roads can double your stopping distance. You must drive slower to stop in the same distance as on a dry road. Reduce speed by about one-third (e.g., slow from 55 to about 35 mph) on a wet road. On packed snow, reduce speed by half or more. If the surface is icy, reduce speed to a crawl and stop driving as soon as you can safely do so.
Identifying Slippery Surfaces. Sometimes it is hard to know if the road is slippery.
Following are signs of slippery roads:
- Shaded Areas. Shady parts of the road will remain icy and slippery long after open areas have melted.
- Bridges. When the temperature drops, bridges will freeze before the road will. Be especially careful when the temperature is close to 32 F.
- Melting Ice. Slight melting will make ice wet. Wet ice is much more slippery than ice that is not wet.
- Black Ice. Black ice is a thin layer that is clear enough that you can see the road underneath it. It makes the road look wet. Any time the temperature is below freezing and the road looks wet, watch out for black ice.
- Vehicle Icing. An easy way to check for ice is to open the window and feel the front of the mirror, mirror support or antenna. If there is ice on these, the road surface is probably starting to ice up.
- Just After Rain Begins. Right after it starts to rain, the water mixes with oil left on the road by vehicles. This makes the road very slippery. If the rain continues, it will wash the oil away.
- Hydroplaning. In some weather, water or slush collects on the road. When this happens, your vehicle can hydroplane. It is like water skiing — the tires lose contact with the road and have little or no traction. You may not be able to steer or brake. You can regain control by releasing the accelerator and pushing in the clutch. This will slow your vehicle and let the wheels turn freely. If the vehicle is hydroplaning, do not use the brakes to slow down. If the drive wheels start to skid, push in the clutch to let them turn freely.
It does not take a lot of water to cause hydroplaning. Hydroplaning can occur at speeds as low as 30 mph if there is a lot of water. Hydroplaning is more likely if tire pressure is low or the tread is worn. (The grooves in a tire carry away the water; if they are not deep, they do not work well.)
Road surfaces where water can collect can create conditions that cause a vehicle to hydroplane. Watch for clear reflections, tire splashes, and raindrops on the road. These are indications of standing water.
Multiple-Choice Questions:
Wet roads can increase stopping distance by how much?
- 10%
- 30%
- Quadruple
- Double
Slippery Surfaces. It will take longer to stop and be harder to turn without skidding when the road is slippery. Wet roads can double your stopping distance. You must drive slower to stop in the same distance as on a dry road. Reduce speed by about one-third (e.g., slow from 55 to about 35 mph) on a wet road. On packed snow, reduce speed by half or more. If the surface is icy, reduce speed to a crawl and stop driving as soon as you can safely do so.
Describe black ice:
- Black ice is a thin layer of jet black ice that hides the road surface underneath and melts at much lower temps than normal ice
- Black ice is a thick, solid layer of ice with an obvious pattern of ringed arcs caused by the weight of vehicles
- Black ice is a thin layer of ice that is clear enough that you can see the road underneath it. It makes the road look wet.
- Black ice is a thin, broken layer of ice that blocks your view of the road underneath
Which of the following is a sign of standing water on the road?
- All of these are signs of standing water on the road
- Clear reflections
- Tire splashes
- Raindrops
Describe hydroplaning:
- It's a strange sensation of grinding or vibrating that makes it difficult to see out the mirrors
- It's a powerful, shaking force that causes the vehicle to bounce violently along the road surface
- It is like water skiing - the tires lose contact with the road and have little or no traction. You may not be able to steer or brake.
- It's a loud and somewhat bumpy sensation caused by the front suspension over-reacting to small imperfections in the road
What is an easy way to help you determine if the road is icing up?
- Open the window and feel the front of the mirror, mirror support, or antenna. If there is ice on these, the road surface is probably starting to ice up.
- The temperature is the easiest way to tell if there's ice on the road. Water freezes at 32 degrees, so if it's below 32 degrees the road must be covered in ice.
- The side of your trailer will always have a sheen on it from the reflection of ice on the road. If the trailer has a sheen to it, the road is icy.
- Watch your tires. If there is spray coming off them, you know the road is icy.
Wet roads can always be slippery, but one of the following conditions tends to be the most dangerous. Which one?
- After it has been raining for a while the roads become extra slick because the water has worked its way into the porous asphalt
- The inside lanes of a four-lane highway are the slickest after the rain stops because they see less traffic
- After it finishes raining and the roads begin to dry, the wet patches are far more slippery because they form on blemishes in the road
- Right after it starts to rain, the water mixes with oil left on the road by vehicles. This makes the road very slippery. If the rain continues, it will wash the oil away.
You cannot steer or brake a vehicle unless you have what?
- Traction
- Momentum
- Automatic Transmission
- Overdrive
If the vehicle is hydroplaning, what's the best way to slow down?
- Don't touch the brakes and immediately steer to the shoulder of the road. Drive on the shoulder as long as necessary to clear the extra water in the road.
- Get on the brakes immediately, but gently at first. Then, with increasing braking force, get the vehicle slowed as quickly as possible
- Do not use the brakes to slow down. If the drive wheels skid, push in the clutch to let them turn freely.
- Get on the accelerator slightly to force the drive tires to accelerate out of the skid
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