When water collects between the tires and the road, the tires ride up on it and lose their grip; that is hydroplaning. Oil streaks and heat-softened pavement can make a road slippery, but they do not cause hydroplaning.
Using the brakes while the tires are riding on a layer of water can send the vehicle into a skid. Lifting off the accelerator and pushing in the clutch lets the vehicle lose speed gradually while the wheels turn freely and regain their grip on the road.
When the tires are riding on water, taking your foot off the accelerator lets the vehicle slow down and the wheels turn freely until they grip the road again. Do not brake to slow down, and avoid extra throttle or sudden steering, which can start a skid.
During dry weather, oil, rubber and grime build up on the pavement, and the first rain turns them into a slick film. As the rain continues it washes much of that residue away, so the road tends to be at its worst right when the rain begins.
Light brake pressure in the water holds the linings against the drums or discs, which helps keep water, mud, and sand out of the brakes. After you are through, keep pressing lightly for a short distance to heat and dry them, then make a test stop when it is safe.
Glare ice leaves your tires with almost no grip, and no braking or shifting technique makes it safe to keep going. The sound decision is to get off the road at the first safe spot and wait until conditions improve.
Black ice is a thin, clear coating that lets the road show through, so the pavement simply looks wet. Any time it is below freezing and the surface appears wet, assume black ice could be there.
On wet pavement, slow down by roughly a third: a truck that would go 45 mph on a dry road should go about 30 mph. On packed snow, cut your speed by half or more.
On slick pavement an engine brake or other retarder can make the drive wheels lose grip and skid, so it should be switched off. Slowing down and planning stops early are exactly what slippery conditions call for.
The car with wavy skid marks warns that the road can become slick when wet. Reduce speed, leave extra following distance and avoid hard braking or sharp steering.
Tires with too little air lose contact with the road more easily and ride up on a layer of water, as do tires with worn tread. It does not take much water, and it can happen well below 50 mph, so even a puddle can be enough.
Slick pavement leaves your tires with little grip, and a sharp or sudden turn can easily break that grip and send the vehicle into a skid. Keep open space beside you in case another vehicle slides, and avoid stopping on a hill, since you may not be able to get moving again on the slick surface.
Black ice forms a coating so thin and transparent that the road beneath it shows through, which makes the pavement look merely wet. When the temperature is under freezing and the road appears wet, assume ice may be present.
Hitting deep or moving water fast can cost you control and soak the brakes. If you must cross, slow down, use a low gear, and keep light pressure on the brakes so water and grit stay out of the linings.
Hydroplaning happens when water collects between the tires and the road, so the tires ride on the water instead of gripping the pavement and the vehicle stops responding well to steering or braking. It can occur even at about 30 mph, and worn tread or underinflated tires raise the risk.
When ice starts to thaw, a thin film of water forms on its surface, and wet ice is much slicker than ice that is still frozen solid. Treat temperatures near the freezing point as especially dangerous: slow down and avoid abrupt braking or steering.
Soaked brake linings can make the brakes weak, grab suddenly, or work unevenly from wheel to wheel, which can rob you of stopping power, lock up wheels, pull the vehicle to one side, or jackknife a trailer. After passing through water, keep light pressure on the brakes for a short distance to dry them.
Engine brakes and retarders can make the drive wheels break traction and skid on a slick surface, so switch them off. Gentle pedal pressure and open space on both sides of the rig are sound habits.
Pooled water can lift your tires off the pavement, leaving you with little or no steering or braking. Clear reflections on the surface and spray kicked up by tires both point to standing water, so ease off the speed and avoid sudden moves when you see them.
Water on the road cuts traction, which can double the distance needed to stop. Speed has an even bigger effect: when you double your speed, you need about four times as much distance to stop, not twice as much.
Every question in this set has its own page with the correct answer and an explanation.
