Alternativelly, if we see the hazard when it's just about us, we need to react in a much more rushed manner and we are bound to be inaccurate and need corrections to at least 80% of our actions. When we plan our reaction in advance, we can react more progressively (since we have the room), and we have the spare space and time to readjust our plans to the changing conditions. Our actual execution will not be spot onto how we planned it but, with a bit of practice, we can reach an efficiency of at least 80 precents. That is a detrimental difference from a method of pure reaction.
Our foveal vision is stretched far ahead, looking practically at the horizon or end of the road section in front, anticipating things that happen (or might happen - like a blind bend that a car might suddenly come around). Than, our mind makes the plan of how to react, and than we use our peripheral vision to judge when and how to execute the plan (when to open up the throttle and how much, when to brake and how hard). It's a three-stage plan:
Anticipation: Look far ahead to see what is about to happen or might happen in advance. This is done by our foveal vision.
Planning: Plan your reaction to what you see in advance
Execute: Perform your plan while double checking to see if it needs to be changed. We use our peripheral vision to gauge our exact inputs.
For instance, a car has stopped in our lane of travel. If we look down and see it only when 40 feet ahead, we would have to stop quickly with little consideration to traffic behind us, and than "restart" and have to merge into the moving traffic in the near lane. If we see it, say, 400 feet earlier, we could see it happening (anticipation) before the car has even stopped, and than plan our moves: Slow down gradually, signal left, check mirrors and merge and than execute our plan.
Speed and Position
For our anticipation, planning and execution to be effective we need to adjust three elements:
Alertness: Lack of concentration eliminates the ability to plan ahead. We need to remain concentration and be even more alert when we observe or anticipate danger or a potential danger.
Speed: If you can see 40 feet ahead but are driving at 60mph, you would be able to anticipate, would you? You need to see things happen at least ten seconds in advance and for this you need to look as far ahead as possible, but also drive in the speed that allows you to detect hazards this early in advance.
Position: We need to adjust our position on the road to suit the conditions: Our margins from other vehicles, our lane and our position in the lane.
Essentially, our anticipation tells us how alert to be, how fast to drive and where to place our cars. It is based on a complex calculation of various factors when we drive, and this has been mentioned elsewhere (the role of anticipation while driving), but the main rule is: "Drive at a speed where you are able to stop well within the distance you see to be clear, and that you know would remain clear." If we can see 100 feet ahead, we need to be able to stop within 80 feet (or less, depending on other variations).
Reading the Road Surface
The grip level of the road surface changes depending on the surface and the car (tires, dampers, load) and external conditions (like heat, dirt) and is expressed as a coefficient of friction (μ), which varies from 0.8 on a good, dry and clean tarmac road with a reasonable car and in reasonable conditions, to as little as 0.1 on ice.
Summary
Dry Tarmac: 0.9-0.65 (up to 2.2 in race cars)
Wet Tarmac: 0.65-0.5
Soil: 0.5
Gravel: 0.4
Run-Off (First Rain): 0.4-0.3
Diesel, Hail, Frost: 0.3
Mud, Snow, Oil: 0.2 (0.35 with snow or mud tires)
Ice, Flooded Road: 0.1. (0.2 can be achieved with studded tires)
Dry Tarmac
From the inscription we can see that the grip levels vary, even on dry roads. The grip levels of a dry road change depending mainly on the quality of the paving: Good tarmac can be significantly more grippy than bad tarmac. Without delving into different types of tarmacadem, good tarmac is normally (but not necessarily) dark-shaded, clean, smooth to ride (no bumps), seems (and sounds) abrasive. Bad tarmac can be dark or grey, might be rough and cracky, and would be smooth and none-abrasive. The different between abrasive tarmac and smooth, shiny-looking tarmac can be quite detrimental.
Another factor to consider is how dirty the road is. Areas of heavy, slow-moving traffic drop oils onto the surface of the road: Cracky gaskets, old filters, cracky head ring of the screw in the oil pan, oil inside the motor (due to cracky cylinder rings), as well as drips of semi-burnt fuel through the exhaust -- all cause droplets of oils, fuel, dirt, tire rubber and alike to drop onto the tarmac.
Other than reducing grip, they also soften the tarmac and accelerate it's wear under car tires, making the road surface polished and not abrasive. There will be more grease is areas in the presence of heavy vehicles like trucks, as well as around slow moving or standing traffic (intersections, winding roads) and in areas where there is a lot of acceleration, deceleration and cornering.
In presence of sand or gravel around the road, like in rural roads near fields or roads that cross the desert, a layer of dust is likely to build up and cause the similar effect. It slightly diminishes around highways where high-speed moving traffic tend to clear the dust off. Roads can also be covered in sand and dust after heavy winds or sand storms, as well as after haze.
A third factor is the temperature. A cold road in a winter morning is going to slippery because the tires don't reach an effective temperature. In countries where it's cold enough to snow in the winter, snow tires are required in the winter even if the road is cleared from snow, because the snow tires can still function at near freezing temperatures much better than summer tires.
According to this rational, a hot road in summer noon would be ideal for grip. This is true when the road is paved well and clear of dirt and grease. If excessive tar was used as a binder in the paving process, or if the road is heavily soaked in grease or dirt, the heat will make the tar or grease melt, diffuse and "bleed" towards the surface of the road. This can be seen as a shiny black surface or even as fumes coming off of the surface ahead.
Lesson learned: Don't treat all roads in the same way. Look at the tarmac and "read" it to estimate how grippy it is, and drive according to the conditions. If the surface of the road seems smooth and polished (not abrasive) and shiny - consider it to be slippery. Slow down slightly and maybe even increase your following distance from traffic in front. Also look down at the painted areas of the road: The white or yellow lines. Against the bright paint, it's easier to judge how dirty the road is, by detecting the presence of dust or a black sticky film or grease on the paint or in the wheel-paths.
In hot weather, you can also see the grease as fumes coming off of the road surface in the distance. The fumes will reflect the sun light in the form of glare that might look like water. When the road is greasy or poorly paved, slow down even more when the road is hot at high noon. The heat makes it worst. Also drive more slowly when the road is cold, especially in the morning and particularly on low-quality tarmac. It's a good idea to consider how bumpy the road surface is and look for patches, and for interlocking "alligator" cracks - this kind of road is bound to have potholes.
Wet Roads
Take a given road surface and soak it in water and you just turned it much more slippery. Quality, abrasive tarmac can sometimes be surprisingly grippy when slightly wet. It's abrasive surface maintains grip and also absorbs and drains the water better. Slippery, smooth tarmac is going to be much more slippery when wet. Also, tires will have a harder time coming to working temperature on such tarmac (lower grip levels mean lower rolling resistance which means less heat buildup). Performance tires are particularly sensitive to such tarmac.
This is not as significant as the presence of grease or dirt on the road. A greasy road turns into a death-trap when it's wet. During the winter, there is usually less grease because it washes during rains. In summer mornings, it can so happen that dew at night time or morning mists will make the road slightly damp and set the grease and dirt afloat. Any other kind of occasional wetness, as well as the first rains of each winter or every time where a small shower of rain comes after a long dry period - will create a "runoff" effect that reduces grip be half of what it normally is on a wet surface.
Runoff can be anticipated where grease of dirt are likely to build up: Mainly inside towns and cities, and especially around intersections, roundabouts, stop signs, bus stops and parking areas. Slow-moving or standing traffic increases the concentration of grease and heavy vehicles like buses and trucks make it worst. Steadily moving traffic, that is not slowing down, speeding up or turning (like on highways) drop little grease.
Beware around towns and in winding roads. Large carriagways can also get slippery of they are full of traffic and trucks. Another area of danger is where there is sand or soil around the road, or near construction sites. Always asses how slippery it is, reduce speed and increase safety margins to suit. Consider any small spell of water after a dry week as "first rain" (other than on motorways). Also remember that the far edges of the road will be more slippery than the center.
Another situation is where the road is heavily covered in water from a serious fall of rain. In this case, all of the grease and dirt are most likely washed off of the surface. But, if the drainage on the road is not as good as it should be, a deep film of water, or puddles, can be created. When the water is deep (and when the speed is high and the tires are worn) the grip levels can be reduced dramatically. Eventually the car can hydroplane, reducing grip to as little as driving on smooth ice.
Beware of deep water: Look at the spray from other cars tires, feel how the car goes through the water and look down at curbs and bumps to see how deep the water is. In areas of deep water, slow down further. Even on a thin film of water, do not drive very fast on a wet road. Limit yourself to 60mph maximum, to avoid hydroplaning. Maintain your tires to the proper inflation pressure and keep the tread deep enough (at least 4 millimeters).
Soil
Be carefull on dirt roads. It's best to avoid them alltoghether. Other than being very slippery, the dirt sticks to the tires for some time and reduces their grip even when you are back on the road. The road is likely to be bumpy and so damage the tires and suspension. Dirt sticks into the rubber bushings of the dampers and little stones get stuck inside the tread and causes damage to the tires.
Dirt roads that have been tightened offer higher grip levels, but also cause cars that slide to lose control more rapidly. Likewise, soil that is covered in grass or similar vegetation will be tighter due to the roots and so be more grippy. On loose gravel, the stopping distance with most ABS systems becomes significantly larger than without ABS. Keep that in mind and reduce speed.
Gravel (little loose stones) is more slippery than dirt. Slow down significantly when so see gravel. Another thing to be careful about is mud. It can either sink the car or be unbelievably slippery. Fertile rustic soil or dry desert sand turn into very slippery mud when wet, just as slippery as snow. Avoid them by all costs.
Snow and Ice
Hail, Frost, Snow and Ice are very slippery. Whenever possible, avoid driving in those conditions. Hail is least slippery, but is quite like driving on gravel or during run-off so be careful. If heavy enough, it can hurt cars, so avoid parking the cars under the open sky when hail or even heavy rain might occur. Frost is a light, powdery white coating on the road, caused by dew that froze during the night. It offers varying grip levels from partial frost (much like hail) to full frost, which is more like proper snow.
Proper snow is very slippery, around the coefficient of friction of 0.2 and nearly twice (!) with snow tires. Fresh, loose, thin snow is relatively grippy, but is still slippery and especially makes the stopping distances with ABS quite long. Slow down to suit the conditions and adjust the following distances. Heavier or colder snow, or snow that has been compacted, will be much more slippery. It's also likely to host a thin layer of even more slippery ice right beneath it. Slow down even more. Rainwater on the road can sometimes freeze into a thin but surprisingly slippery film of snow, and slush (snow mixed with mud and dirt) is very slippery, as well.
Proper ice is a different story. There are special studded tires for ice driving. Sometimes, small, thin patches of ice that were under the snow will remain unmelted in the shade of trees or inside puddles of water. This ice is often thin enough to be nearly completely transparent, thus being called black ice. Be careful where black ice is likely to build up (high altitudes, shaded road areas, on and under bridges, inside tunnels, in wet areas or near melting snow. Alternatively, ice can form into a smooth layer, particularly around 7 degrees celsius, where it is most slippery. Don't drive on such ice, ever.
Snow or ice tires (as well as mud or terrain tires) function badly on dry roads. Using snow tires in the summer or dry season, results in increased wear to the tires, which could also go beyond the working temperature or suffer a blow-out. Also, under heavy braking, where we need our tires the most, the rubber will begin to melt down under the tire and increase the stopping distances significantly, especially when the road is hot (but even in normal temperatures). Always use the proper tires for the job.
Oil
Every now and than, a serious collision occurs because a truck driver left behind a big pool of dropped oil on the road unattended and another driver slipped over it. While clearly not the driver's fault, this kind of collision can be avoided by properly reading the road surface. Other than just judging how grippy the road is (and therefore at what speed to drive over it and what margins to maintain from other cars), the purpose of reading the road surface is to be ready for these rare cases, should they occur: A large sheen of oil or diesel drooped onto the road, a big puddle of slippery mud or a big patch of ice, or even just a big crack or pothole - are all mortal hazards that are posed by the road itself.
Look far ahead and observe changes of color. Ice can be seen by it's brightness and oil can be seen as a dark fluid or as a rainbow or spectrum of colors (thin-film interference), especially when mixed with water (when it's most slippery). As you see something like this, slow down. When you have established that it's oil, mud, ice or anything else that poses a genuine hazard to you, slow down as best as possible, with consideration to the traffic behind. If possible, even perform a full emergency stop. If there is a clear escape route (like the hard shoulder of the road) use it to brake.
If you cannot stop safely in front of the hazard, slow down as best as possible and try to go around it. If you can't do this safely either, slow down as best as you possibly can, and than cross the slippery area (or the pothole) without any force applied onto the car: Don't brake, don't accelerate and especially do not steer. Try to keep the car balanced on light throttle (so that it is not slowing down or speeding up) and keep the steering straight or as straight as possible. If you must slow down to avoid another hazard beyond the slippery area, do it gently. ABS and Stability Control (ESP) can help dealing with such hazards.
Anticipate the possibility that the car might slide. If it does, either brake hard or try to recover from the slide. Drivers that don't have the necessary skill and regular practice at car control should brake hard, rather than try to recover. Their attempts at recovering would be infertile and might even make things worst. Braking immediately could stop them very quickly or even resolve the slide.
http://www.articlesbase.com/automotive-articles/reading-the-road-surface-5272909.html
