We don't actually drive the car with our eyes, we do it with our hands and feet. However, it is our eyes that recieve the information that would lead the hands and feet and synchronise them. Using the eyes properly is the greatest single element that carries the greatest impact on our performance. This article will delve into this subject and explain it thouroughly.
Our human tendency, as it is developed in a walking pace of less than 20 kilometers per hour (our mind works at about 6km/h), is to look down at our immediate surroundings. When driving this tendency is our biggest limitation. When we look down, we physically cannot see further ahead, and when our speed increases the amount of information we "get in" becomes even smaller, and we get a stronger sensation of speed that causes us to let go of the gas at a subconcious level, as well as even cause serious motion sickness. By looking up we can see further ahead or be aware of the presence of something on the road ahead faster and in advance. This means that, for a given speed, we can see things that require us to react (like an obstacle in our path) before we actually need to react. This gives us time to PLAN our response in advance, ready ourselves and only than react, rather than respond immediately.
If we react to anything on the road without planning, we will have to make corrections to almost all of our driving inputs. If we learn to plan ahead, soon enough we would be able to perform most of our inputs of steering, brakes and acceleration with no need for corrections - an increase in efficiency by about 80%! We will always have a "safety margin" that will allow us to readjust our plans when things on the road ahead change, and even if something happens suddenly, we will be in a position of readiness and react much quicker, sometimes 2-3 seconds faster.
We can ready ourselves and execute our plans gradualy, with control and awareness to everything. For instance, instead of finding out about the obstacle in the last possible second and having to perform a screatching stop, with little control of the traffic behind or besides us, we can realize that we about to negotiate an obstacle 15 or even 20-30 seconds in advance, gauge the amount of braking necessary and, at the right moment, brake more graudally, while also paying attention to traffic around us. We have enough times to change our plans.
This kind of vision also has a significant impact of dynamic aspects of driving (unlike the "peripheral control" aspect described above). Looking further ahead down the highway, as an example, makes our mind draw the most straight-lined imaginary path between ourselves and our remote point of focus at the horizon. If we were to look relatively close to our car, we would be much more jerky and "wonder" along the road as if it was a slalom course. Also, whenever we stray from our desired course, like if we slide, looking further ahead will make us more aware of this slide. If we look ten feet ahead, and the car starts to slide, we won't notice it before the car starts to spin. If we look four hundreds feet ahead, every little unplanned yaw of the car will redirect our vision and shift our focus much more notably.
We can go as far as to say that, when stress is undergone, a driver will steer the car towards the point where his focus lies. This makes the driver unable of avoiding an obstalce in front simply because fear makes him look at what he does not want to hit, rather than to the place where he wants to swerve to. The problem with looking at what you don't want to hit, is that your actual desire is not only to avoid hitting it, but rather to avoid it by "hitting" a certain clear space besides it. Instead of steering away from where we don't want to go (without any indication as to when and how much to steer), we want to steer towards where we do want to go.
Foveal and Peripheral Vision
The mere question of "where" or "how far" to look towards does not grant us the whole answer, if we do not ask ourselves "how" to look. The human eye provides us with two kinds of sight: Our foveal vision, coming from the "Fovea Centralis", which is a big "spot" across the eyeball, and our peripheral vision. The foveal vision is our small field of focus, which allows to notice details. The peripheral vision is a much wider, often subconcious, field of vision that appears blurred, but can be effective in noticing objects as "smears" of color and gauging distances and speed of motion, as well as being very sharp in detecting sudden change of motion or color.
Because of the different traits of these two kinds of sight, we need to learn to use each of them effectivelly. Since our foveal vision can notice details, noticing detail allows to make plans based on those details. So, our foveal vision should provide us with the planning that we described earlier and, as such, it should be directed towards the direction of travel and far ahead. Our peripheral vision is used for timing and precision. We need to use it to determind exactly where to open up the throttle in the corner and just how much. We basically use it to affirm the plans that we have made earlier.
Of course, we sometimes need to focus on details that appear in the mid-range. This is relevant for driving in city streets or in heavy traffic in general. In these situations we want to develope a scan pattern between the further point which we can see to be clear, on the road ahead and down to a certain point in the foreground near in front of us. The "foreground" is a professional definition for an area which is close to us, but not necessarily in front of our wheels. There is no point in looking down to an area of the road which we cannot stop in front of. Depending on our speed, we need to asses how quickly we can stop in an emergency. Our "foreground" point should be located just beyond this range and we will scan the road up an down, up and down, up and down, left to right, up and down and so on ad infinitum, between that point on the foreground and the furthest point up ahead.
On open highways with good visibility, and likewise in winding roads or on driving circuits, we need to "filter out" irrelevant information by looking up to the furthest point we see to be clear, on the road ahead, and not performing a repetitive scan pattern across our visual field. Filtering out the unnecessary or superflous information allows our mind to focus on the important bits and allows us to drive faster without so-called "ground rush."
Speed and Position
One of the most important applications of the proper use of vision, is to know at what speed we need to be traveling and where to put our car over the road. We look ahead to anaylze the road conditions and to decide how dangerous it is, why, and what to do with it in terms of our speed and position (or, pace and line). The variables we need to include in this calculation are multiple, but they are governed by the basic principal of: "Driving at a speed where you can always stop well withing the distance you see to be clear, and that you know would so remain clear." If we are able to see 400 feet ahead, we need to adjust our speed to be able to stop within, say, 360 feet, as an example. However, it's important to acknowledge that the actual calculation is much more complex. It includes multiple variants, such as:
Observation
Our looking ahead is not going to be very useful unless we use it to facilitate proper observation and planning. We need to take in mind every hazard on the road ahead, and any potential hazard that might be in store. The article on last month's issue, about avoiding "unavoidable" collisions - gives some good examples of how to anticipate. You see a junction 400 feet down the road: Look at the traffic lights. Are they green? Will they stay green untill you get there? How much traffic is moving with you? What is the potential of danger of this segment of road? Do you have any reason to believe that a driver from crossing traffic might run red at you? Or otherwise could a driver alongside you decide to make a right or left-hand turn suddenly, right in front of you?
Dynamic Aspects
When talking about using our vision in dynamic aspects, we are talking about corners and also about emergency skills and limit handling. Our way around bends, on the road and track is a good starting point for this kind of discussion. As we come up to the bend (well in advance before the corner itself) we need to take a quick look besides us and across the bend (where possible) and as far down the road behind it as possible. Even if we cannot see the road itself, we can often see it's general route through "hints" such as car lights or car roofs over the verge, a "skyline" of tree-tops, telegraph lines or light poles, the formation of the guardrail or the formation of the mountain-side.
This allows us to avoid surprises around unknown bends, or to better asses known bends, too. By looking besides us and around the bend, we actually see, with our very eyes, the circumference of the bend, which enables us to asses it's steepness much better. It can also help facilitate so-called "cognitive map" thinking where we sketch the form of the bend in our mind from a bird's eye point of view. It only takes one quick peek (though it might take more than one) and than we return to forward vision and focus on the limit point.
It's a learned skill to look into the corner, even if it means looking through the side window rather than the windshield. If we are looking straight ahead through the bend, we are not looking far enough down the bend, and we also fool our mind into thinking that we are still driving straight. This leads to problems like speeding in the bend or bad timing of corner entry. The limit point is the thing that limits our ability to see down the road and beyond the bend. Instead of looking to the further point we see to be clear, we look further down, towards what's obstructing our view, and we watch the road "unfold" at us as we get closer.
The advantage is that there is a reduced tendency for our eyes to "scroll down" as they focus on any certain object, and also, we are able to asses the corner and the required speed much better. The limit point would appear to us as an "arrowhead" that would begin to unfold and get away from us as we draw nigh it. From this point we need to adjust our speed so that we are "in pace" with the movement of the limit point, and remain so. If, mid-corner, the limit point seems to "decelerate" it would mean that the bend becomes tighter. If it accelerates away from us, the radius of the bend increases.
The key is to visualize our desired route around the corner and through the limit point. Once we see our desired apex of the corner (a subject we covered in the chapter about cornering lines) we need to lift our vision beyond the limit point and beyond the bend itself, again looking as far ahead beyond it as possible. This allows us to straighten up the car more smoothly coming out of the corner, as well as to ready ourselves and plan ahead in the case of successive cornering.
On a racing circuit, the technique becomes even more subtle. The track driver has permenant, fixated objects used as "reference points" as to where he brakes, turns, accelerates, hits the apex and exit the corner. The idea on the track is to take a peek around the corner and than focus on the driver's turn-in point. As we get closer to the turn-in point (about the time where we perform the downshift) we shift focus up to the apex and our actual turn-in point is gauged with our peripheral vision (which, I remind you, is the one in charge of timing). As we get close to the apex marker (by the time where we transition from trail-braking to balanced throttle) we shift focus away from the apex and up to the exit, and clip the apex with our peripheral vision. As we are about to reach the exit, we look up along the following straight, looking for the next corner.
If the car starts to slide, it's important to remain focused at the reference point or the road ahead. Novice drivers can find benefit in choosing a remote, fixed and notable object to focus on as a "target." By keeping the eyes aligned with the right direction (even if it means looking through the side window) we are at a much better position to get our car back on the right track.
Reading the Road Surface
Another task for our vision to perform is to read the road surface and asses it's grip levels. This is important for adjusting the right speed and position, but becomes ever more vitaly important in those rare cases where there is a patch of dangerously slippery pavement up ahead, whether it's because a rig has dropped oil over the pavement or an icy patch has been formed somewhere on the road.
The best grip levels are offered by small cars wtih quality tires, over a good surface of tarmac, and can reach a maximum coefficient of friction of 0.9. Grippy tarmac is usually dark-shaded, and appears to be abrasive and often has a distinctive noise. Low quality tarmac is usually grey and looks smooth and none-abrasive and you can see lights and cars reflected over it. Concrete also tends to yield a lower coefficient of friction. There are two more important elements: How hot the tarmac is and how dirty it is.
During the hot season, the tarmac tends to become covered in dirt and soaked in grease from the vehicles. This softens the tarmac and increases it's wear, but also results in lower levels of grip. The effect is intensified when the road is hot. The time to worry about this is about half-way through the summer, especially in high noon or during heatwaves. The dirt can be seen as a sticky black film covering the road, and can often be seen more clearly against the bright painted lines on the road (the yellow line or the lane markers). Hot, greasy roads also tend to ommit vapour that makes you see the reflection of the sky up ahead.
The effect is further intensified around water. Look out for drips originating from fountains or sprinklers, as well as in the morning due to nightly dew or morning mists. Also beware around sand: Roads crossing deserts or fields are prone to have less grip, as well as any road during a sand storm or haze. Another situation to look out for is a cold road, also less grippy because tires don't make it to their effective range of temperature. This is relevant to winter morning, even when perfectly dry.
A wet road can generate a wide range of grip levels, depending on the depth of the water film and again, on the quality of the tarmac below it and the amount of dirt on it. Look out for small spells after a dry period of, say, a week. The effect is much more profound around areas of slow-moving traffic (intersections, bus stops, roundabouts, curved roads) and especially heavy traffic, or in the presence of sand. Look for dirt or grease on the water, especially over the yellow shoulder line where it tends to drain. Even a normally wet road can have low levels of grip. Look out for deep water, and look to the pavement to get an idea of how deep it is. Another indication is the thickness of the spray from another car's tires.
Dirt roads are even more slippery. Look for smooth, tight dirt than to loose gravel or stones or light sand and beware of sticky mud, or mud puddles that can either stall the car or make it slide out of control. Grassy areas tend to be more stable due to the roots.
Snow and Ice are the most challenging conditions, and they should not be tackled without the proper tires. Snow tires can increase the grip levels from a mere 0.2 to 0.35 or even slightly more. Fresh snow tends to be more grippy and allows to stop quite quickly when desired. Colder, more dense snow, as well as compacted snow or slush - tends to be more slippery. Hail or frost yield higher grip levels, more like a wet road than a snowy one.
Proper ice is the most problematic condition. It offers the lowest possible coefficient of friction, much lower than that of most oils, if they are to be spilt on the pavement (as much as three times more slippery than diesel on the road!). Look out for smooth, shiny ice at a temperature of about minus 7 degrees celsius - it is most slippery. When coated with snow ("sheet ice") or when it is partially molden, it tends to be more grippy, but not by much.
The important thing is to look out for any patch of ice (mainly so-called "black ice"), or puddles of mud or dropped oil that somehow made it's way over the pavement. Look far ahead and detect any shiny substance. Look out for ice in tree shades or over bridges and overpasses, as well as under small puddles of water or remains of melting snow. Look for grease by it's distinctive spectrum of colors: Dropped oil tends to form into a colorfull sheen (due to "thin-film interference") that, if large enough to threaten us, will be seen from a distance. Now, you have the time and space to slow down or plan your way around the obstruction, or adjust your line over it as safely as possible.
Our human tendency, as it is developed in a walking pace of less than 20 kilometers per hour (our mind works at about 6km/h), is to look down at our immediate surroundings. When driving this tendency is our biggest limitation. When we look down, we physically cannot see further ahead, and when our speed increases the amount of information we "get in" becomes even smaller, and we get a stronger sensation of speed that causes us to let go of the gas at a subconcious level, as well as even cause serious motion sickness. By looking up we can see further ahead or be aware of the presence of something on the road ahead faster and in advance. This means that, for a given speed, we can see things that require us to react (like an obstacle in our path) before we actually need to react. This gives us time to PLAN our response in advance, ready ourselves and only than react, rather than respond immediately.
If we react to anything on the road without planning, we will have to make corrections to almost all of our driving inputs. If we learn to plan ahead, soon enough we would be able to perform most of our inputs of steering, brakes and acceleration with no need for corrections - an increase in efficiency by about 80%! We will always have a "safety margin" that will allow us to readjust our plans when things on the road ahead change, and even if something happens suddenly, we will be in a position of readiness and react much quicker, sometimes 2-3 seconds faster.
We can ready ourselves and execute our plans gradualy, with control and awareness to everything. For instance, instead of finding out about the obstacle in the last possible second and having to perform a screatching stop, with little control of the traffic behind or besides us, we can realize that we about to negotiate an obstacle 15 or even 20-30 seconds in advance, gauge the amount of braking necessary and, at the right moment, brake more graudally, while also paying attention to traffic around us. We have enough times to change our plans.
This kind of vision also has a significant impact of dynamic aspects of driving (unlike the "peripheral control" aspect described above). Looking further ahead down the highway, as an example, makes our mind draw the most straight-lined imaginary path between ourselves and our remote point of focus at the horizon. If we were to look relatively close to our car, we would be much more jerky and "wonder" along the road as if it was a slalom course. Also, whenever we stray from our desired course, like if we slide, looking further ahead will make us more aware of this slide. If we look ten feet ahead, and the car starts to slide, we won't notice it before the car starts to spin. If we look four hundreds feet ahead, every little unplanned yaw of the car will redirect our vision and shift our focus much more notably.
We can go as far as to say that, when stress is undergone, a driver will steer the car towards the point where his focus lies. This makes the driver unable of avoiding an obstalce in front simply because fear makes him look at what he does not want to hit, rather than to the place where he wants to swerve to. The problem with looking at what you don't want to hit, is that your actual desire is not only to avoid hitting it, but rather to avoid it by "hitting" a certain clear space besides it. Instead of steering away from where we don't want to go (without any indication as to when and how much to steer), we want to steer towards where we do want to go.
Foveal and Peripheral Vision
The mere question of "where" or "how far" to look towards does not grant us the whole answer, if we do not ask ourselves "how" to look. The human eye provides us with two kinds of sight: Our foveal vision, coming from the "Fovea Centralis", which is a big "spot" across the eyeball, and our peripheral vision. The foveal vision is our small field of focus, which allows to notice details. The peripheral vision is a much wider, often subconcious, field of vision that appears blurred, but can be effective in noticing objects as "smears" of color and gauging distances and speed of motion, as well as being very sharp in detecting sudden change of motion or color.
Because of the different traits of these two kinds of sight, we need to learn to use each of them effectivelly. Since our foveal vision can notice details, noticing detail allows to make plans based on those details. So, our foveal vision should provide us with the planning that we described earlier and, as such, it should be directed towards the direction of travel and far ahead. Our peripheral vision is used for timing and precision. We need to use it to determind exactly where to open up the throttle in the corner and just how much. We basically use it to affirm the plans that we have made earlier.
Of course, we sometimes need to focus on details that appear in the mid-range. This is relevant for driving in city streets or in heavy traffic in general. In these situations we want to develope a scan pattern between the further point which we can see to be clear, on the road ahead and down to a certain point in the foreground near in front of us. The "foreground" is a professional definition for an area which is close to us, but not necessarily in front of our wheels. There is no point in looking down to an area of the road which we cannot stop in front of. Depending on our speed, we need to asses how quickly we can stop in an emergency. Our "foreground" point should be located just beyond this range and we will scan the road up an down, up and down, up and down, left to right, up and down and so on ad infinitum, between that point on the foreground and the furthest point up ahead.
On open highways with good visibility, and likewise in winding roads or on driving circuits, we need to "filter out" irrelevant information by looking up to the furthest point we see to be clear, on the road ahead, and not performing a repetitive scan pattern across our visual field. Filtering out the unnecessary or superflous information allows our mind to focus on the important bits and allows us to drive faster without so-called "ground rush."
Speed and Position
One of the most important applications of the proper use of vision, is to know at what speed we need to be traveling and where to put our car over the road. We look ahead to anaylze the road conditions and to decide how dangerous it is, why, and what to do with it in terms of our speed and position (or, pace and line). The variables we need to include in this calculation are multiple, but they are governed by the basic principal of: "Driving at a speed where you can always stop well withing the distance you see to be clear, and that you know would so remain clear." If we are able to see 400 feet ahead, we need to adjust our speed to be able to stop within, say, 360 feet, as an example. However, it's important to acknowledge that the actual calculation is much more complex. It includes multiple variants, such as:
- Road Surface: A tarmac road, built of dark, abrasive tarmac and clear of any dirt, will enable us to stop faster, so we can drive at a faster speed that we could on lower-quality tarmac (one that is grey, shiny and slippery) or on a wet or snowy road. Also, a worn, patched road surface might mean that you would have to slow down or stop down the road due to poteholes.
- Road Conditions: If a given road surface is covered in dirt, water or snow and ice, it would require slowing down accordingly.
- Visibility: Is the weather providing you and the other drivers with clear vision? Is there so much as a mountain's side shadow, or low afternoon sun? Maybe there is a dust storm? Is it raining or even foggy? Adjust your speed according to the ground rule.
- Road Width: How many lanes in each direction? A wider road allows to drive faster than a one-lane road. Is there a median between the opposite directions of traffic? Obviously if there is one you could drive faster. I would even go far as to asses just how rigid it is, as to decide how fast I wish to drive.
- Safety Margins: Does the road has a shoulder that allows to use it as an escape route? Is it paved, or is it a "soft" gravel shoulder instead? Obviously you can drive faster if the road has a paved shoulder, depending also on how wide it is. If the shoulder is unpaved, you need to asses how slippery it is (is there grass, grass or mould along the road?) how wide it is, and how significant are the height differences between it and the road. In either case, you also need to adjust your speed when the shoulder is occupied by stopped vehicles or by other obstructions.
- Safety Measures: Is there a safety guardrail? Is it a concrete "New Jersey Wall" or an energy-abosrbing metal rail? Adjust speed to fit. In tunnels, slow down because there is no shoulder, no energy absorbing rail and it's harder to rescue injured people from it.
- The Direction of the Road: Is it going uphill or downhill? How stepply? Is is curving to the right or left and how steeply?
- Potential of Danger: What are the typical hazards that you anticipate in this kind of road? When driving near a school, you need to be in a position of readiness for young pedestrains running out, even in the foreground. On a rural road, oncoming traffic or wild animals are more likely to be encountered.
- Traffic: What are the conditions of the traffic around you? Is it dense or light? Is it flowing, condensing or jammed? Is it mainly light cars, or are there a lot of trucks, rigs or bikes? What is the speed of traffic? Can you 'flow' with it? Is there oncoming traffic nearby?
- Driver's Personal State: Are you fully concentrated and alert? Or maybe you are upset? Perhaps you have just started driving and your concentration levels haven't stabilized yet? Maybe your whole family is inside the cab, making noise and movements that distract you?
- Condition of the Car: Does the car give you the desired safety of being able to stop quickly and being easily manueverable. Do you suspect that something in the tires or suspension is due to replaced soon, and is currently not giving you the fullest potential of grip? Or is the car perhaps loaded in passengers and cargo in a way that makes it's stopping distances longer? Is there ABS? how effective is it? Is there ESP? Is there EBD? Perhaps the car's passive safety (protection of it's occupants in a crash) is not very good either?
It sounds like a lot, but you quickly learn to take all of this data into account and choose how fast to drive and where to put our car on the road (the right lane? The left lane? Where along the width of the lane itself?).
Observation
Our looking ahead is not going to be very useful unless we use it to facilitate proper observation and planning. We need to take in mind every hazard on the road ahead, and any potential hazard that might be in store. The article on last month's issue, about avoiding "unavoidable" collisions - gives some good examples of how to anticipate. You see a junction 400 feet down the road: Look at the traffic lights. Are they green? Will they stay green untill you get there? How much traffic is moving with you? What is the potential of danger of this segment of road? Do you have any reason to believe that a driver from crossing traffic might run red at you? Or otherwise could a driver alongside you decide to make a right or left-hand turn suddenly, right in front of you?
Dynamic Aspects
When talking about using our vision in dynamic aspects, we are talking about corners and also about emergency skills and limit handling. Our way around bends, on the road and track is a good starting point for this kind of discussion. As we come up to the bend (well in advance before the corner itself) we need to take a quick look besides us and across the bend (where possible) and as far down the road behind it as possible. Even if we cannot see the road itself, we can often see it's general route through "hints" such as car lights or car roofs over the verge, a "skyline" of tree-tops, telegraph lines or light poles, the formation of the guardrail or the formation of the mountain-side.
This allows us to avoid surprises around unknown bends, or to better asses known bends, too. By looking besides us and around the bend, we actually see, with our very eyes, the circumference of the bend, which enables us to asses it's steepness much better. It can also help facilitate so-called "cognitive map" thinking where we sketch the form of the bend in our mind from a bird's eye point of view. It only takes one quick peek (though it might take more than one) and than we return to forward vision and focus on the limit point.
It's a learned skill to look into the corner, even if it means looking through the side window rather than the windshield. If we are looking straight ahead through the bend, we are not looking far enough down the bend, and we also fool our mind into thinking that we are still driving straight. This leads to problems like speeding in the bend or bad timing of corner entry. The limit point is the thing that limits our ability to see down the road and beyond the bend. Instead of looking to the further point we see to be clear, we look further down, towards what's obstructing our view, and we watch the road "unfold" at us as we get closer.
The advantage is that there is a reduced tendency for our eyes to "scroll down" as they focus on any certain object, and also, we are able to asses the corner and the required speed much better. The limit point would appear to us as an "arrowhead" that would begin to unfold and get away from us as we draw nigh it. From this point we need to adjust our speed so that we are "in pace" with the movement of the limit point, and remain so. If, mid-corner, the limit point seems to "decelerate" it would mean that the bend becomes tighter. If it accelerates away from us, the radius of the bend increases.
The key is to visualize our desired route around the corner and through the limit point. Once we see our desired apex of the corner (a subject we covered in the chapter about cornering lines) we need to lift our vision beyond the limit point and beyond the bend itself, again looking as far ahead beyond it as possible. This allows us to straighten up the car more smoothly coming out of the corner, as well as to ready ourselves and plan ahead in the case of successive cornering.
On a racing circuit, the technique becomes even more subtle. The track driver has permenant, fixated objects used as "reference points" as to where he brakes, turns, accelerates, hits the apex and exit the corner. The idea on the track is to take a peek around the corner and than focus on the driver's turn-in point. As we get closer to the turn-in point (about the time where we perform the downshift) we shift focus up to the apex and our actual turn-in point is gauged with our peripheral vision (which, I remind you, is the one in charge of timing). As we get close to the apex marker (by the time where we transition from trail-braking to balanced throttle) we shift focus away from the apex and up to the exit, and clip the apex with our peripheral vision. As we are about to reach the exit, we look up along the following straight, looking for the next corner.
If the car starts to slide, it's important to remain focused at the reference point or the road ahead. Novice drivers can find benefit in choosing a remote, fixed and notable object to focus on as a "target." By keeping the eyes aligned with the right direction (even if it means looking through the side window) we are at a much better position to get our car back on the right track.
Reading the Road Surface
Another task for our vision to perform is to read the road surface and asses it's grip levels. This is important for adjusting the right speed and position, but becomes ever more vitaly important in those rare cases where there is a patch of dangerously slippery pavement up ahead, whether it's because a rig has dropped oil over the pavement or an icy patch has been formed somewhere on the road.
The best grip levels are offered by small cars wtih quality tires, over a good surface of tarmac, and can reach a maximum coefficient of friction of 0.9. Grippy tarmac is usually dark-shaded, and appears to be abrasive and often has a distinctive noise. Low quality tarmac is usually grey and looks smooth and none-abrasive and you can see lights and cars reflected over it. Concrete also tends to yield a lower coefficient of friction. There are two more important elements: How hot the tarmac is and how dirty it is.
During the hot season, the tarmac tends to become covered in dirt and soaked in grease from the vehicles. This softens the tarmac and increases it's wear, but also results in lower levels of grip. The effect is intensified when the road is hot. The time to worry about this is about half-way through the summer, especially in high noon or during heatwaves. The dirt can be seen as a sticky black film covering the road, and can often be seen more clearly against the bright painted lines on the road (the yellow line or the lane markers). Hot, greasy roads also tend to ommit vapour that makes you see the reflection of the sky up ahead.
The effect is further intensified around water. Look out for drips originating from fountains or sprinklers, as well as in the morning due to nightly dew or morning mists. Also beware around sand: Roads crossing deserts or fields are prone to have less grip, as well as any road during a sand storm or haze. Another situation to look out for is a cold road, also less grippy because tires don't make it to their effective range of temperature. This is relevant to winter morning, even when perfectly dry.
A wet road can generate a wide range of grip levels, depending on the depth of the water film and again, on the quality of the tarmac below it and the amount of dirt on it. Look out for small spells after a dry period of, say, a week. The effect is much more profound around areas of slow-moving traffic (intersections, bus stops, roundabouts, curved roads) and especially heavy traffic, or in the presence of sand. Look for dirt or grease on the water, especially over the yellow shoulder line where it tends to drain. Even a normally wet road can have low levels of grip. Look out for deep water, and look to the pavement to get an idea of how deep it is. Another indication is the thickness of the spray from another car's tires.
Dirt roads are even more slippery. Look for smooth, tight dirt than to loose gravel or stones or light sand and beware of sticky mud, or mud puddles that can either stall the car or make it slide out of control. Grassy areas tend to be more stable due to the roots.
Snow and Ice are the most challenging conditions, and they should not be tackled without the proper tires. Snow tires can increase the grip levels from a mere 0.2 to 0.35 or even slightly more. Fresh snow tends to be more grippy and allows to stop quite quickly when desired. Colder, more dense snow, as well as compacted snow or slush - tends to be more slippery. Hail or frost yield higher grip levels, more like a wet road than a snowy one.
Proper ice is the most problematic condition. It offers the lowest possible coefficient of friction, much lower than that of most oils, if they are to be spilt on the pavement (as much as three times more slippery than diesel on the road!). Look out for smooth, shiny ice at a temperature of about minus 7 degrees celsius - it is most slippery. When coated with snow ("sheet ice") or when it is partially molden, it tends to be more grippy, but not by much.
The important thing is to look out for any patch of ice (mainly so-called "black ice"), or puddles of mud or dropped oil that somehow made it's way over the pavement. Look far ahead and detect any shiny substance. Look out for ice in tree shades or over bridges and overpasses, as well as under small puddles of water or remains of melting snow. Look for grease by it's distinctive spectrum of colors: Dropped oil tends to form into a colorfull sheen (due to "thin-film interference") that, if large enough to threaten us, will be seen from a distance. Now, you have the time and space to slow down or plan your way around the obstruction, or adjust your line over it as safely as possible.
