A modest little tome, found at: http://homepages.enterprise.net/ijs/biking.html
The Author (well, he didn't put his name in the downloadable
bit, so why should I go looking for it?) said:
"Here are the first three chapters, to read, save, or print as you
wish."
I did and here it is:
People ride motorcycles for a variety of reasons. For some it's a question of simple economics; small motorcycles are astonishingly cheap to run compared to all other forms of powered transport.
For some people the motivation to try two wheels is provided by traffic congestion on their route to work. Commuting by motorcycle is almost always quicker than any alternative.
Some riders are genuine enthusiasts who also involve themselves in the sporting side of motorcycling. They've discovered that the sheer exhilaration which comes from riding a modern sports bike is simply not provided by any other class of vehicle. The drivers of exotic sports cars can only dream about commanding the sort of power-to-weight ratio that motorcycle riders now take for granted.
Since the early Seventies another group of riders has evolved. The despatch rider has become a familiar sight on the roads of Britain, and thousands of us now make our living by moving through the increasingly dense traffic more effectively than anybody else.
I think it's reasonable to claim that career minded despatch riders eventually build up a wealth of experience which is unequalled by any other group of riders, with the possible exception of police motorcyclists. Despatch riders unquestionably ride more miles, but police motorcyclists receive the benefit of excellent training, and as a consequence of attending the scenes of road traffic accidents they are bound to learn from the mistakes of others. These advantages are not available to couriers.
However, despatch riders are compelled to analyse the risks they face because their incomes and their lives depend on knowing what will happen next in any situation, and the purpose of this book is to reveal the secrets involved in riding a motorcycle for a vast mileage in such a way that these risks become acceptable. What follows is a despatch rider's view of traffic: the suggestions put forward are based on my experience of riding for 20 years, and 650,000 miles, in London and the home counties.
I'll attempt to describe every situation of risk that confronts you, and suggest the way of dealing with it which will provide the greatest margin of safety. A few of the situations described are extremely rare and may never be encountered, but most are all too common.
I hope the suggestions will be enlightening for novice riders, especially those who intend to commute to work throughout the year, or perhaps to try their hands at riding motorcycles for a living. And I'm sure that riders with several years' experience won't be disappointed.
A few of the points made will be relevant to riders living in sparsely populated areas of the country but since more than 90% of my work involves riding in and around London, I claim no expertise in dealing with fox hunts, muck spreaders, herds of sheep (or is it flocks?), and other mysteries of the deepest countryside.
Welcome to the real world of black cabs spewing diesel as they perform daring U-turns, Post Office vans with unused indicators, wayward pedestrians, and harassed car commuters who divide their attention between the traffic outside, and their lap-top computers.
On the next three pages I've set out some basic principles of survival. Unfortunately this does require a rather serious start to the book, but the points made are of vital importance and I'll introduce terms here which will be used in later chapters. Once these points are taken on board, you'll find the rest of the book much more readable.
When you're riding a motorcycle it's possible, but unusual, to be involved in an accident that's completely beyond your control, for example, when somebody simply fails to see you coming and pulls directly into your path. Or when you stop at a red light or a pedestrian crossing, but the driver behind doesn't.
It's maddening that in such situations your survival can be in someone else's hands, but apart from these very exceptional cases, your safety is within your control. There's a method that will ensure your safety in all normal situations and it's based on maintaining a clear path ahead.
The Highway Code includes the following sentence.
"Never drive so fast that you cannot stop well within the distance you can see to be clear."
This is excellent advice, and it constitutes an acceptable short form of a First Rule for drivers, but because we're so vulnerable, we need to analyse the principle involved here in much greater depth.
Three statements are needed to express the First Rule for motorcyclists.
1. At whatever speed you're riding, you must be aware of your stopping distance. 2. Your path ahead must be clear of actual or possible obstruction throughout your stopping distance. 3. You must be able to assess the condition of the road surface throughout your stopping distance.
Obviously that lot hardly trips off the tongue, and to encapsulate all this in a simple sentence is difficult but, so long as you remember all that the First Rule implies, a short form is acceptable, so let's work with this one:
Ride so that you maintain a clear view of your path ahead throughout your stopping distance.
If you can ride so that you never contravene this First Rule, you will eliminate virtually all risk.
You've probably noticed that I've used the term stopping distance, and not braking distance. Stopping distance includes the distance travelled during reaction time, which is the time that elapses between the point at which you notice the need to stop, and the point at which you actually apply the brakes. Typically this is around 0.6 seconds so, even at only 30 mph, you'd travel 26.4 feet before applying the brakes. That's about the length of two small hatchbacks, and sometimes you'll be accelerating throughout this distance. Of course, your reaction time will be longer if you're tired, cold, unfit, or simply not concentrating.
Your braking distance is affected by the condition of the road surface, and you'll find there's a complete chapter dealing with this issue.
Of course, it's much easier to state the First Rule than it is to observe it when you're riding in dense traffic. But throughout the book I'll attempt to define a riding style that involves positioning yourself so as to obtain the maximum safety margin in any traffic situation.
Before looking at specific traffic situations we need to come to terms with a problem that confronts us constantly. When I outlined the principle of the First Rule, I stated that "Your path ahead must be clear of actual or possible obstruction throughout your stopping distance". In reality, if you maintain a separation of this length between yourself and the vehicle in front, you sometimes find that you're overtaken, or that the driver behind follows you so closely that you're put at risk.
In practice, when the vehicle in front is an ordinary car, you can usually see your path ahead over its roof, past the sides, or through the glass area, and in this position it's acceptable to follow at a distance equal to the distance travelled during your reaction time, plus a few feet for your safety margin.
It's best to increase this distance slightly if the road is wet, because the car's wet weather braking performance may be superior.
The problem is, you can't see over, or through, all vehicles. When the vehicle in front is a van, a bus, a coach, or any heavy goods vehicle, the only way to be absolutely safe is to leave a gap that's equal to your overall stopping distance, because the "opaque vehicle" obscures all dangers.
This is extremely difficult in modern traffic conditions. The traffic density is now so great that it's usual to find drivers maintaining a separation of only 30 or 40 feet even when travelling at motorway speeds.
If the vehicle in front of you is, say, a Transit, and you're following it at 60 mph in the outside lane of a motorway or dual carriageway, intending to overtake when it pulls back in, the gap you need to leave in order to comply with the First Rule is a little over 230 feet. And if you maintain a gap of this length on a road such as the M25 in the rush hour, the driver behind is likely either to drive within a few feet of your number plate and flash his lights, or to overtake you on the inside and cut back in sharply. He may then jab his brakes momentarily just for fun.
There's not really anything you can do about this except to drop back and allow the gap to increase to a safe distance again. Try to console yourself with the fact that if he drives like this routinely, he'll soon be caught on camera and prosecuted.
A second problem with opaque vehicles is that they hide you from the view of other road users. And sometimes when they change lane, or turn off at a junction, you're suddenly seen for the first time by a driver who's now accelerating towards your roadspace. In this situation you become a "revealed hazard" and this is something which is covered in detail later in the book.
It's impossible to overstate the extent to which opaque vehicles endanger motorcyclists. Riding close behind an opaque is equivalent to riding with your hand in front of your face. I think it was James Hunt who referred to the slower cars on a race track as "mobile chicanes". From our point of view opaque vehicles constitute "mobile blind spots".
Motorcycles generally travel faster than opaque vehicles and it's common to see riders following closer behind, not farther behind HGVs, anxious to overtake quickly and be out of the fumes. This is safe only if you position yourself either to the inside, or to the outside of the vehicle from where you can see your path ahead. If you maintain a position between these extremes and there's debris on the carriageway, you'll be unable to avoid it when the vehicle passes over it.
Another problem with opaque vehicles arises when they pull up at the side of the road to unload goods, or passengers. In this position they hide road signs from your view and there's no simple way to overcome the problem.
In practice, whenever you pass an opaque vehicle that's parked at the side of the road, especially on a stretch that you're not familiar with, it's safest to assume that it is obscuring a sign indicating a hazard ahead, and ride cautiously until you're confident that any danger is passed.
We can't win a battle with HGVs, and in any case they're far more important to the economy than motorcycles are, even those used by couriers. So defensive riding is the logical strategy, and this will be defined throughout the book.
This chapter is all about the road surface. But I hope you'll agree that the title I've chosen focuses the mind usefully. Having only two wheels seems to be a major advantage when you're threading your way through heavy traffic. You can afford to smile a little at those around you stuck in their metal cages. But when you stop at the lights and have to put your foot down to keep from falling over, or park the bike and have to use a stand to prevent it crashing to the ground, it's the watching drivers who probably smile. You're riding a device which is so unstable that it won't even stay upright: the limitations are obvious, and it's no wonder so few people are prepared to attempt to master the things.
To ride a motorcycle you have to balance the forces involved constantly. This process is largely unconscious, yet you're aware that a moment's failure to do so would spell disaster.
The forces you're dealing with are acceleration, momentum, centrifugal force, gyroscopic effect, gravity, deceleration, and air movement. Except when you're riding in a straight line, at a constant speed, and with a tail wind of equal velocity (a rare combination), most of these forces oppose you. They act to try to break the grip of your tyres on the road, and this is why the quality of the road surface is so important to you.
We're fortunate to live in a country where most road users can take for granted that the standard of road surfacing is sufficiently high to ensure their comfort and safety. In recent years the financial constraints imposed on many local authorities have led to falling standards and postponement of some repairs, but it's pleasing to see, for example, that Shellgrip is still routinely applied in areas of high risk such as the approaches to pedestrian crossings and traffic lights. And this special, high-grip surface coating can often be found on roundabouts, and adverse camber bends. Clearly without these surface refinements you would be at much greater risk.
So, if a good surface is usual, and grip isn't a problem, you need to concern yourself with what's unusual.
But before considering what is unusual, how to predict where you'll find it, and how to deal with it when you do, a vital point needs to be acknowledged. Since you can't make an objective assessment of the road surface without seeing it properly, you need to observe the First Rule at all times, and so maintain a clear view of the road surface throughout your stopping distance.
Incidentally, this requirement demonstrates that high speed riding in the dark is indefensible.
If the road surface is normally clean, dry tarmac offering good grip, then the unusual conditions that concern you include: water, frost, ice, snow, wet leaves, mud, grit, polythene bags, fuel spills, animal droppings, subsidence, overbanding, and debris.
Before looking at these hazards in turn, mention should be made of the white lines which demarcate lanes, junctions, verges, parking bays etc., and the areas of white cross hatching which separate opposing streams of traffic. While these markings have the intentional property of being highly visible, the white materials used seem to vary from borough to borough and some offer virtually no grip when wet.
It's also common to find mini roundabouts and pedestrian crossings made from materials that are slippery when wet, and wheel-spin may be experienced here even on machines with little power.
To increase your safety margin it's useful to be able to predict where the surface hazards listed above are most likely to arise, so let's look at each one in turn. It's not possible to put them in order based on the frequency of encountering them, because there are too many variables, but I've grouped together first those that involve water in one form or another.
WATER
When it's raining you naturally accept that the surface is wet and offers less grip, especially after a long dry spell, so you ride accordingly, leaving an increased separation for braking, and tackling bends and junctions more slowly. But during dry weather you may still encounter water on the road surface.
Common causes include: car washes, cooling system leaks, street cleansing vehicles which often operate near markets, the activities of the fire service, hosing-down of the road after an accident or carriageway repair, window cleaners emptying buckets, and leaking stopcocks under those metal covers (gravel or mud on the road often accompany this one). Keeping an eye on the clouds will give early warning of wet roads ahead caused by an isolated cloudburst, and remember that long after rain has stopped falling you may still come across water dripping onto the road under bridges, gantries, trees, underpasses and in tunnels. Also, vehicles will carry water into tunnels for a hundred yards or more.
Incidentally, wet patches on dry roads are often more visible in the dark because they reflect light sources.
FROST
Frost is fairly visible, so it shouldn't present you with too many surprises. It's usually encountered in the morning when you're riding in to work, melts slowly during the warmer daylight hours, and may reappear as darkness falls. Because it only occurs in very cold weather when you'll be aware that your tyres are also very cold and don't offer their maximum grip, you shouldn't come upon an area of frost riding fast and leaning far over on a bend.
Points to note are that while cars and other vehicles will erase frost for each other, you're likely to be riding on different areas of the carriageway. Also, long after the frost that's been exposed to sunshine has melted, you'll still find frost present in areas shaded by trees, buildings, fencing, or a parked vehicle (which may have been driven away seconds before you arrived on scene). Remember too that the sun's movement means an area now enjoying sunshine may have been in the shade until thirty minutes ago.
As usual, if you're uncertain about the amount of grip available, an exploratory dab with your boot on the road surface can tell you a lot. This is a useful technique worth practising, but remember it's always done with your foot behind, or to the outside of the footrest, never in front of it.
THE RIDING SURFACE
ICE
Ice presents the ultimate surface hazard. Grip is virtually absent. It can be expected to form initially on stretches of the carriageway that are exposed to the cold from underneath as well, such as flyovers and bridges. Dips in the road may hold frozen puddles, and openings in walls and hedgerows will permit cold wind to blow across and chill the road surface.
Listen to the weather forecasts; they may predict a sudden cold spell following rain. A bird-bath or a jar of water placed in the garden will confirm below zero overnight temperatures before you get on the bike in the morning.
Watching vehicles ahead for unusual movements such as snaking, or sliding down the camber, can provide early warning of ice but ultimately, if you have reason to believe that ice is probable, there's no justification for riding. Control over your survival will be taken out of your hands and placed into the hands of following drivers. This is because you'll slow right down if you suspect ice ahead, but following drivers of cars and heavier vehicles will not feel at equal risk, and in frustration they'll follow closer and closer behind, impatient to pass. If you do encounter ice and fall they'll be unable to stop, or to swerve round you.
SNOW
Falling snow is horrible stuff to ride through. Apart from the disturbing visual effect, it can obscure lamps and indicators, screens and visors within a hundred yards or so. Using your glove to wipe them will lead to a frozen hand within a few miles, and nothing mists up so readily as the inside of a visor that has snow on the outside.
Car drivers have wipers to clear their screens, of course, but snow still presents them with a problem. The wipers push some of the snow to the right-hand side of the windscreen, up against the A pillar, and this creates a marked blind spot. You need to bear this in mind when you're approaching a vehicle whose driver is waiting either to pull out from a side turning on your left, or to join a roundabout.
The effects of snow settling on the road surface can be rapid and dramatic. Road signs, cat's-eyes, road markings of all sorts, and even the kerbs can become obscured in minutes. This can lead drivers to believe they have right of way across your path when they don't, and you could make the same mistake. And don't forget that some pedestrians suddenly prefer walking in the road to walking on the pavement when there's snow on the ground.
There are different types of snow. The sort that's good for snowballs because it sticks together so well, will fill in the tyre tread pattern and quickly build up under the mudguard. This leads to a lessening of grip on the road surface and a growing braking effect from the compacting snow between the tyre and guard. The result will be that the wheel stops turning.
If snow is settling rather than melting, all of the considerations relating to ice will apply. If you consider your journey is essential despite such extreme conditions, it's worth carrying sufficient funds for an enforced stay at a hotel.
A heavy fall of snow overnight can cause another problem. When leaving for work, car drivers will clear snow from windscreens, and hopefully rear and side windows, but it's quite usual to leave it on the bonnet and roof.
I think the motivation for this is probably a heroic display of how tough were the conditions that these drivers have had to overcome. There isn't a problem at the low speeds achieved as they drive through the housing estates or villages where they live, but if their journey to work includes a stretch of dual carriageway, or motorway, the situation is altered.
You don't want to be behind one of these snow-covered cars when it reaches the critical speed at which the snow on the bonnet, or the roof, lets go. The stuff on the bonnet may suddenly ride up onto the windscreen, overcoming the wiper motor and removing all vision. Anything from a violent swerve to an emergency stop in an attempt to dislodge it, is now possible. If the snow on the roof lets go when you're behind, you could be struck in the face or the chest by anything up to a hundredweight of the stuff.
An HGV can present a slightly different risk, particularly if it's being used for long-distance work. It may deposit a large quantity of snow from its roof onto the carriageway in an area of the country where no snow has fallen. Predicting this would be virtually impossible; and that's why we have the First Rule.
Incidentally, all vehicles will occasionally drop large chunks of slush, or ice, from under their wheel arches onto the carriageway. This can happen anywhere, not just where the road surface is uneven.
WET LEAVES
Wet leaves offer almost no grip and this condition persists long after it's stopped raining. This is because the top layers prevent evaporation, and hence drying, from the lower layers.
Although it might seem obvious that their presence could be predicted by the time of year and the proximity of trees, remember that when dry, leaves can be blown some distance.
In the spring, fallen blossom can present a similar hazard.
MUD
Mud varies in colour and character depending on soil type. Farmers probably find this fascinating. But our interest lies in being able to predict where it will be found on the carriageway.
In the countryside you expect to come across mud on the road fairly often. It's likely near farms, fords, field gates, forestry tracks, and on lanes with high banks on either side, particularly during and after rain.
But in urban areas mud on the road is uncommon enough to catch you out unless you can predict its presence. Road works will often lead to mud on the surface and warning signs should be erected by the contractors, though they may be blown over if it's windy.
Where there are no warning signs, other give-aways include: contractors' vehicles parked by the verge, piles of road mending materials, workmen's huts, drums of cable, lengths of pipe, etc.
Astute riders will notice bunching and gaps in the oncoming traffic caused by Stop Go boards or temporary traffic lights.
Incidentally, the planed surface that's often encountered near large-scale road works produces a disturbing effect; your bike will wander and feel exactly as though it has a puncture. But the greater danger may come from the raised metalwork that's left proud until the road is resurfaced. This can cause a real puncture. And if the roadworks involve excavation you might come across metal plates, as large as eight feet by four feet, set into the surface. Naturally these offer almost no grip when wet.
If you see parked vehicles bearing the sign writing of cable television providers, British Telecom, gas, water, or electricity companies, this usually indicates that the road is being dug up, so mud is likely.
And mud is almost certain to be deposited on the road near the entrances to landfill sites, and refuse transfer stations, by the lorries that go in and out repeatedly.
In towns and cities you can expect to find mud near construction and demolition sites. Early indicators include cranes visible ahead, skips, and parked lorries waiting either to deliver building materials or to carry away rubble and spoil.
GRIT
Grit, gravel, litter thrown from vehicles, cigarette ends and wind-blown debris tend to migrate to the kerbside, and the middle of the road around traffic islands, bollards and the central reservation. These are the areas not driven over by other vehicles but only by cyclists and ourselves when filtering through heavy traffic to gain advantage.
Obviously this debris offers a poor braking surface. Also it offers poor grip to the sole of your boot and this creates a problem when you filter right to the front, along the outside of a line of traffic, to be first away at the lights. On a machine with a high centre of gravity (or a full fuel tank) there's a strong possibility of toppling over as your supporting foot slides away from you.
This is one of the rare instances where it's acceptable to use your left foot for support, with the bike in gear and the front or rear brake held on.
POLYTHENE BAGS
If you've yet to encounter a polythene bag lying on the road as you brake or lean into a bend, you might easily dismiss the danger they present as insignificant, or improbable. In fact the problem is growing, especially now that so many local authorities provide large, black bags as dustbin liners.
These tend to be stuffed into garden hedges and fences only to be removed by schoolchildren or the wind shortly afterwards, and many of them end up lying in the road.
Your front tyre will grip the upper surface of a bag reasonably well. And the weight of the machine presses the lower surface into the road. But the two inner surfaces slide across each other with virtually no friction, allowing your wheel to slide sideways if you're leaning or braking.
Some veteran despatch riders suspect a cunning plot to wipe out the competition we present. The stratagem used is to leave large, nylon, Post Office sacks lying casually on the streets of London. But in truth, the wind is probably to blame. These sacks are routinely left on top of pillar boxes.
FUEL SPILLS
Fuel spills are a frequent cause of motorcycle accidents. With petrol we're at least comparatively fortunate that the fairly rapid evaporation of the fuel limits the risk, but diesel fuel doesn't evaporate readily, so it presents a more lasting danger. And it's worrying to note how many people now opt for the diesel version when buying a new vehicle.
Spillages are mainly due to ill-fitting or missing filler caps. When the vehicle negotiates a bend, a roundabout or a junction, fuel surges towards the outside of the vehicle and may escape from the filler neck. This type of spill can only occur where a vehicle follows a curving path; but three point turns, U-turns, and vehicles entering or leaving premises at the sides of the road are all reminders that curving paths are sometimes followed on straight sections of road.
You have to expect fuel spills near filling stations, bus and coach depots, and the yards of haulage contractors and other operators of fleet vehicles who may have on-site refuelling facilities.
Leaks from the fuel line, filter housing, pump or injectors can deposit the substance anywhere on the carriageway, and concentrations will occur where the vehicle has been slow moving or stationary.
An obvious point is that if you come across a fuel spill on, say, a left hand bend, you can expect the stuff on successive left hand bends.
Large spills can sometimes be detected first by smell, but if you're observing the First Rule you'll be studying the road surface and shouldn't be caught out.
Not only fuel and fuel oil, but also lubricating oil can leak and drip from vehicles. The dark patch along the centre of lanes surfaced with concrete bears witness to this. Incidentally, the changing intensity of the darkness betrays dips and bumps ahead, as drips are dislodged. The effect is also concentrated where vehicles slow and stop, so bear this in mind when positioning yourself and braking at junctions, roundabouts and traffic lights, particularly if it's wet. Lay-bys and parking areas are acutely affected by oil leaks.
And if you see the flashing orange light of a breakdown recovery vehicle ahead, it's worth remembering that many breakdowns are accompanied by the loss of lubricating oil onto the carriageway.
ANIMAL DROPPINGS
Animal droppings pose a foreseeable hazard in the countryside where not only farm animals but wildlife too is ever present. Cattle markets and abattoirs are also obvious sources of the problem.
But for riders more used to urban conditions, horses are the only common culprits for this peril and they can be expected near riding schools, police stations, at carnivals, military displays and similar special events. A few scrap merchants, brewers and department stores still employ horses on a local basis.
SUBSIDENCE
Subsidence affecting the carriageway is fairly unusual but it can occur where modern traffic imposes loads on earlier subterranean public works, such as Victorian brick sewers, which were not envisaged by the original engineers.
Another cause of subsidence is where water is leaking from an underground water main and washing away the supporting soil. In the countryside heavy rain may overburden underground water courses and produce a similar effect.
In towns and cities, sunken inspection chamber covers and potholes are the main worry and, as usual, observing the First Rule is the best defence.
Though not caused by subsidence, there is another surface imperfection to watch for. "Tramlines" are worn into the surface of the nearside lane, on trunk routes, by the sheer weight acting through the tyres of large goods vehicles. Ride between the two sets.
OVERBANDING
Overbanding is the smooth, mastic like substance that's used to make good after road repairs, and to seal the openings made by slot cutters when laying under surface cabling. Logically it should be manufactured with a contrasting colouring agent to make it more conspicuous. But this is the real world where most people don't ride motorcycles and are not at risk, so it's the same colour as tarmac.
Most riders have probably experienced the result of encountering a strip of overbanding on a wet bend. The front wheel slides sideways three or four inches and then hopefully regains grip. A dab with the inside foot may be needed to save the day.
But another danger exists in wet weather when you're filtering between lanes on a straight section. Overbanding is commonly laid in almost continuous strips between lanes, so if you're forced to brake, both wheels may stop turning.
When accelerating, or braking, try not to cross strips of overbanding at a shallow angle.
DEBRIS
Encountering debris on the carriageway is something many riders don't seem to accept as a possibility, let alone a probability. They follow so closely that if something lying on the road is revealed as the vehicle in front passes over it, no avoiding action is possible. In fact, if you ride far enough, almost any object will be seen eventually. Traffic cones, the carcasses of lorry tyres, and complete or partly smashed pallets are commonplace on motorways and near motorways, and parts of exhaust systems and wheel trims can be expected on any road.
Any item that can be carried on an open backed lorry or pick-up truck can fall off the back, particularly where the road surface is poor, or at a hump-backed bridge. At places where the vehicle follows a curving path, items may fall sideways.
Have you ever seen a skip that wasn't filled above the rim? And have you ever seen a skip lorry driver carefully fitting a tarpaulin over the skip so that nothing could fall or be blown onto the road?
The abuse of roof racks, at holiday time and near to those out-of-town superstores, is another obvious source of this problem. At the beginning of this chapter I mentioned the various forces which act on your machine, continually testing your skill at balancing them. Remember that when riding downhill, if you come across a patch of surface offering poor grip, the force of gravity magnifies the peril in relation to the steepness of the decline.
Where there's potential danger from one of the sources mentioned here, it's generally easier to avoid getting into a skid than it is to get out of one. And remember that where you're unsure of the grip a particular surface offers, a dab with the sole of your boot can provide useful information.
It's asking a lot, but try to have some idea of the surface presented to people coming the other way too. They may swerve to avoid something, or skid towards you. And if you'll be coming back that way soon it's nice to have advanced warning of possible trouble spots.
Finally, if there's a biker following you and you spot danger on the
surface, point to it, to alert him.
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