If the freedom of speech is taken away then dumb and silent we may be led, like sheep to the slaughter.

- George Washington

Saturday, 23 October 2010

Rider Visibility

'Zaphod' made an interesting comment to a recent post, and rather than reply at length (as I think his comment deserves it) I thought I would start a new topic. The original post concerned the often negative consequences of 'safety' improvements, but the comments thread drifted somewhat into Risk Compensation Theory and road safety issues.

Zaphod said...

Does anyone have a viable solution to the "Sorry-mate-I-didn't-see-you" problem? Anger is justified, but doesn't actually help; and I see the point about lights and unintended consequences.

Riders always assuming that they haven't been seen, that's a bit unrealistic? I give bikers a nod when I'm waiting at a junction, so they know that I've seen em. That makes their life a little easier, but doesn't solve the big problem. And what about the one that I won't see, one day?

I read once that sailors are aware that anything on a collision course doesn't move relative to the background. That sounds a bit complicated, but it's important.

Car drivers- When coming out of a junction, don't just rotate your head. Move it about a foot, side to side. This gives your stereo vision an 18 inch baseline, instead of 6 inch. If you don't follow that explanation, just do it. It works. Make it a habit. Every little helps. Bikers don't want to die, and drivers don't want to kill.
I am assuming that Zaphod is writing from a car driver's perspective. My response would be:

A viable solution to the SMIDSY problem is indeed to ride on the assumption that you are invisible. If you assume that no-one has seen you, and that they may do anything within the laws of physics in front of you, then you are pretty safe from other motorists who actually haven't seen you. In effect, you have compensated for their lack of observation before the event.

To give an example which is a frequent occurrence near me at the moment: traffic lights controlling some road works on a major route, with long tailbacks of stationary cars and lorries occupying the nearside lane. A common error for riders is to see the offside lane clear and assume that they can ride up it as long as no-one is coming the other way because it's for opposing traffic, right?. What often happens is that a car driver gets frustrated and decides to do a U-turn and try another route. He doesn't check his offside mirror because no-one will be coming up behind him because it's for opposing traffic, right? (same error) and pulls out to make a sharp turn. The rider is caught unawares and T-bones the car in the side. He has effectively hit a solid stationary object, and the consequences for the rider can be severe. Oscar India described a similar incident here recently [1].

If the rider assumes a) that no other motorist is aware that he is there, and b) any other driver may do anything at any time, then the rider will perform this manoeuvre with great caution, by riding slowly past the stationary traffic, and as far away from the queue as possible - on the far side of the offside lane. If a driver does do something unexpected, firstly you are travelling slowly enough to be able to take avoiding action, and secondly the distance from the traffic queue means that you have the maximum room to work in.

That's the ideal, but none of us is perfect. If the situation happens on a regular basis (and I guess city riding and constant filtering are an extreme example), then the rider will travel a little quicker and perhaps a little closer - familiarity breeding contempt, and all that. That increases the risk, but it also increases the advantage of the bike to deal with congestion, so each rider will find his or her own level of risk/benefit ratio. But the principle remains - it's safest to assume that you are wearing a Harry Potter Cloak of Invisibility. To answer Zaphod's point - yes, it may be unrealistic to ride like that all the time, but riding according to the principle is by far the safest way to ride. And he is dead right in saying that anger (other than at yourself for your stupidity) serves no purpose in this kind of situation.

Nodding to acknowledge that you have seen a rider is appreciated - that's thoughful behaviour, and we would all wish that all car drivers were similarly aware of other road users. Personally, I will 'ride invisible' until I am sure that a car driver has seen me, either by such a nod, or by positive eye contact. After that, I will move a little more confidently, but still with caution. We have all known a situation where a car driver has looked us straight in the eye, and then pulled into our path anyway.

Zaphod's comment about car drivers moving their heads is a good one. Bike magazine did some research a few years ago in collaboration with SafeSpeed which demonstrated exactly this point. Recent car design, and especially the concern for protection in a roll-over accident, has led to the A-pillar of new cars (the one between the windscreen and the front windows) being much thicker than it used to be. This has two important consequences for car/bike interactions:
  • The A-pillar is thick enough to represent a bike-length at a distance of about 20m - in other words, at normal traffic separation distances, the bike can be completely hidden behind the pillar, and
  • The motion of a car pulling onto a roundabout and the simultaneous motion of a bike going round the roundabout can coincide so that the bike remains hidden for about 50m of travel - long enough for the driver to pull out and hit the bike which he has never seen, despite looking.
The advice that the magazine gave [2] was that drivers should do exactly what Zaphod suggests - look deliberately on both sides of the A-pillar, moving the head to do so. The main check should be round the front of the pillar, to avoid the risk of 'opposite tracking' a vehicle in the blind spot. Bikers can assist the process by being highly visible - high-viz clothing and headlights on dipped beam are the usual suggestions. I'm not a big fan of the high-viz approach, but I can see the logic here. Another thing riders can do (and I can recommend this, as it works) is to change course slightly. This works best if you are approaching a junction on a straight road, with a car waiting to pull out. The small profile of the bike and rider don't give enough information to the driver about approach speed and direction (compared to say a truck, which gets bigger very quickly as it approaches), but the eye is always attracted to something that moves from side to side. Just doing a gentle weave as you approach the junction makes you instantly visible to the driver. (He may just assume you are drunk or out of control, but the end result is the same: he knows you are there.)
Bikers don't want to die, and drivers don't want to kill.
This is spot on, and I am glad for a bit of debate that is co-operative rather than hostile. Car drivers can help by looking out for bikers, and bikers can help by realising that car drivers may not always have seen them for good reasons, and even if they have looked propely and not roar up into people's blind spots and act as if the whole world owes them safe passage.

(The reference to sailors and collision courses is correct, too. If you spot another vessel heading across your course, you take a compass bearing on it. If you take another compass reading in a few minutes and it is the same, then you and the other vessel are on a collision course. One or both of you should take avoiding action.)

[1] A good biking blog. He doesn't post often, but when he does it is always thoughtful and intelligent.

[2] Link to the SafeSpeed website here, which gives screenshots of all of the above, plus artciles by Spen King (designed of the Range Rover) and others, and a general review of the SMIDSY phenomenon. Worth a read.


  1. Riding defensively is your only hope. For example, long straight roads with high cover on either side give you expansion of visual texture effects to beat what scared the shit out the guy in 2001 when he was between dimensions. So, you just want to open up because on roads like that, er, '70' mph looks like 270.

    At your peril. Baxter's Law holds that, half way down, such roads will always emit a tractor or a Volvo, either or both always driven by Helen Keller.

  2. Conversely, of course are the roads in places like Lincolnshire, where the lack of 'features' by the roadside (unless you count a mud-filled ditch as a 'feature') leads to to think you are going far slower than you are. All to do with parallax. So you give it some, and round the next corner is -

    Helen Keller, you said it.

  3. Another aid that bikers can adopt to increase self-preservation is colourful clothing & helmet.

    Not necessarily a fluorescent Hi-Viz jacket, but at least leathers & helmet that are not 'black', matt or camouflage-pattern.

    As a frequent car-driver on the rush hour M25 'fast'-lane (when it's anything other than), I'll always indicate 'right' when I see a biker behind, to let him know it's safe to pass on my near-side.

    Without fail, I get a grateful acknowledgement.

  4. Trouble is, black is so cool :)

    Pity more car drivers aren't as helpful as you. Not that they should be passing on the nearside, of course! But anything that helps each other get along is OK in my book.

    One cultural thing: in the UK, riders normally wave with the left hand, as it closer to the driver they have just overtaken. On the continent, they do it with the right leg (if they waved with the right hand, the bike would stop). It's actually a gesture of thanks, but for years I thought they were angry with me. A waving boot is easily misinterpreted.

  5. Hi Richard

    1. Black may be 'cool', but it's a bloody nightmare to spot when you're a bike-aware driver; for the other 95% of ignoramouses sat behind a wheel it's Casus belli of SMIDSY.

    Perhaps that's the origin of the term "Dead Cool" ;-)

    2. When the motorway's solid with 3 lanes of cars & trucks crawling or even moving 50-ish to 60-ish, the relatively safest place for the bikers is usually between lanes 2 & 3. [I say usually, because there are so many impatient car/van lane-hoppers, & it's those who are the most dangerous, particularly if they haven't spotted the biker.]

    3. I alway's wondered why some did the 'Rossi' acknowledgement, albeit with right- rather than left-leg.

  6. Yes indeed. Any colour you like so long as it's black.

    Thanks for the link to the Odd Dogs Richard.
    A post shall be appearing there shortly indicative of the nature of the eternal. The news is not good. It never is.

    A pint of the finest shall be yours when next you visit Glasgow. The Solid Rock is the place for man-bikers in their prime to go. Broad- minded young women eager for the wisdom of the ages frequent that place.

  7. I've had that link there for ages, I think. I get a lot of traffic from your place, and I thought it would be polite to return the favour :) I still can't work out what the heck it all means (your site, I mean) but I always visit when you have a new post. It reminds me that I must be relatively sane. I don't always comment, because sometimes I am lost for words.

    Thanks also for the offer of a pint in Glasgae. I'll be the closest to Glasgow I have been for many years next weekend (family wedding near Newcastle) but I'm afraid I won't have the time to push further North on that occasion. Maybe when I get going on my Round Britain Whizz. I'll have a can of Tesco's Finest Lager right now instead. Cheers! Put a broad-minded young woman to one side for me, OK?

  8. I don't know what it means either. Your recent post about a secret online diary chimed a chime deep where I keep my chime monitoring equipment, probably the same place that chyme monitoring... oh no, leave that there - people might be eating.

    A broad-minded woman shall be placed on reserve. For some reason the same broad-minded women mostly wear short skirts, high boots and a lot of eye-shadow in that place. This seems to interest broad-minded men.

    I just go in out of the rain for a cup o tea and a read o the Daily Record masel.

  9. The young woman (actually, she doesn't have to be all that young) sounds good. I had to do a double take on your "a lot of eye-shadow in that place". I was thinking "why would they wear eye-shadow down there?"

    Garn, forget the tea and have some nice Tesco's.

  10. Visibility is a big, complicated topic and probably the only conclusion that can be drawn is that it almost entirely depends on context. So much so, that the only sensible way to proceed is indeed as though you have not been seen. Often enough, it's true.

    Consider that, for another road user to allow for your behaviour:
    1. They must have been looking
    2. They must have seen you
    3. They must have correctly identified what they have seen
    4. They must have correctly analysed your speed and trajectory
    5. They must react appropriately to all of the above.

    Yes, it's the sort of calculation your brain is quite good at, and is constantly performing, but...
    1. As we know, not always the case. Human error, carelessness, something more interesting happening elsewhere...
    2. All sorts of parallax effects, occlusions and so on may apply. A-frame blindness is a particularly good example.
    3. Now, this is where the whole clothing and visibility debate gets a bit tricky. All-black is actually pretty good. It presents a recognisable and entire silhouette, and in any case, peripheral vision is primarily in black-and white due to the structure of the eye. It's not great against a black background, of course. Hi-vis bits and pieces may (note: may) stand out more, against a uniform background, but a selection of bright flashes of colour does not necessarily constitute a recognisable object. There is no one answer: it depends where you are and what the background is.
    4. Not always easy. Non-bikers genuinely seem to have no idea how much performance capability a bike has. They work with what they know: how long it would take their car to pull away, or cover a given distance, for example. Headlights can be a positive handicap in this sort of situation, by masking the size and shape of the approaching bike that would otherwise help indicate how close it is and how quickly it is getting closer.
    5. And then, some people will do it anyway. People who don't understand right of way. People who make mistakes. Joyriders. Etc.

    Multiply all of that by the number of interactions wih other road users that you have each trip, and it's pretty clear that the sensible money is on you, as an individual, not relying on anyone else's input to your safety. Being noticed - and having someone else act courteously as a result - is a bonus. That's why I thank them, as much as anything: because it's not expected behaviour.

    And, as a biker, it's not a bad idea to remember that all too often, whether you've been seen or not, your vehicle can do things that many motorists are completely unequipped to predict accurately. The best survival skill you can learn is when to moderate the throttle and be patient.

  11. +1 to your last sentence. Couldn't agree more.

    I would take slight issue with your remark about headlights. I find a headlight is pretty useful in identifying a bike in the distance, although I'm not a big fan of hard-wired lights. I find a dipped beam doesn't affect my perception of the bike, it just draws my attention. However, I am a member of a mainly US-based forum, and they are all very big on main beams, and even modulators. I've had any number of arguments over there on this subject. I ask them why it is a good idea to dazzle someone who is driving a 3-ton vehicle in your direction, and why it is a good idea to piss off every other road user, but all they can say is (I paraphrase) "I don't care if I annoy them; at least they have seen me". I find the whole attitude dreadful, to be honest, but it also ignores the research I have seen (sorry, no link) that suggests that a bright light such as a main beam actually makes it harder to estimate location and speed than a moderate light such as a dipped beam. That would accord with my own experience.

    Useful analysis of the visibility/perception thing. The Police even have a category for it: Looked But Did Not See.

  12. Richard why do you think drivers need to 'identify a bike in the distance'? It is when they are meters away on a converging trajectory that they need to have identified a bike and if they can't see us by then a headlight will make precious little difference.

    (+1 to endemoniada_88's comments too.)

  13. I'm tempted to say that they might not be metres away on a converging trajectory if they had seen the bike earlier.

    I'm not sure I see your point here. Why wouldn't a driver or rider want to identify an approaching vehicle as far away as possible?

    (Let's be clear. I am not a particular advocate of hard-wired headlights. I can see an marginal advantage in certain circumstances, but not enough to switch the lights on on any bike where I have the option, unless visibility is poor.)

  14. I don't think there is much benefit in 'seeing' an approaching vehicle more than around 5 seconds away from the potential conflict point (which is 220 ft at 30mph) as too much can change in the meantime for it to be of any use.

  15. ....and you are on a potentially converging trajectory with all sorts of vehicles all the time.

    Mostly nothing happens though!

  16. This is all surprisingly scientific!

    A thought on headlights-
    I remember hearing of an early military experiment in camouflage. Very counter-intuitive, and (unsurprisingly) I don't think anything came of it.
    The idea was to disguise ships in daylight by putting a few very bright lights on them. What? Something to do with spoiling the characteristic silhouette. A casual glance, (most glances are casual), would not engage the conscious attention. Hmm. Bike with headlight on?

    Vision is much poorer than we think. Most of the vivid picture in our head has been extrapolated from assumptions and irregular updates from the wandering eye. Movement and edges can call your attention to threats. We put too much faith in that internal picture.

    One morning I spent half an hour searching for the teapot. It was in front of me, right where it always is, but I'd forgotten that the blue one was broken, and new one was yellow. Couldn't find a blue thing anywhere.

    How about a stronger version of those flickering LEDs that bicycles have? It's not vivid, but it's kinda unusual and the subconscious might soon make the association? It would probably turn out to be illegal though.

    Stop wearing black? No chance! Let's be realistic.

  17. @Voyager - a lot can change in the last 5 seconds, sure, but that doesn't mean that any info before that is of no use. If good driving/riding is about anticipation, then the more warning you get of a vehicle the better. It's only marginal, as I have said above, and I don't want to defend the 'you must have your headlight on or you will die' approach. But in some cases it might make a small but significant difference. When you consider the sheer number of conflicting trajectories we encounter every day, it's a wonder any of us gets home at night :)

    @Zaphod - it's a quality blog, this! You are quite right about the lights on ships - disrupting the outline is the key to 'hiding' the object. As Endo says above, maybe a full black outfit is actually better then a multi-coloured one because it presents a clear and recognisable silhouette.

    As to flashing lights, I believe that any flashing light is illegal in the UK except for emergency vehicles (anyone?). The ones worn by cyclists are certainly highly visible, although they used to be illegal if mounted on the bike (hence all the helmet and sleeve attachments) although that may have changed. Headlight modulators (which switch the main beam between 20% and 100% power 4 times a second) are also illegal here. The American riders seem to love them.

    Personally, I have a bit of a philosophical objection to all of these things. They are heading in the direction of putting responsibility for my safety onto other people - you must have seen me, and therefore you must take avoiding action - leading, in an extreme case, to the ridiculous attitude of "I had my headlight on full power and was wearing high-viz clothing, therefore it can't have been my fault".

  18. Clearly (haha), this is an interesting field of debate, and is full of paradox and subjective thought.

    looking vs seeing
    size vs distance
    speed vs relative velocity
    mobile phone in hand vs control

    As a frequent visitor in Athens, a city where motorcycles are used in great numbers by everybody in all social classes (except perhaps those on the hit list viz. politicians, lawyers and bankers), I can but surmise that it's the shear numbers of these bikes on the roads that makes other road users more generally aware. I'm not saying that motorcycle travel is safer in Athens and considering the general lack of grip on polished asphalt I'm surprised that anyone can ride on it at all(I speak from personal experience).

    So my crazy idea is to wear a giant neon/led flashing halo with my name in lights (as depicted in the most recent TV campaign)

    Have a good day everybody!

  19. Ah, so it was you in City Madness, was it? I believe that was shot in Athens. You can hear him spinning up the rear wheel at times, which agrees with your comments on the state of the roads. Awesome riding, proud to have you on the blog, frankly.

  20. You flatter me - little point on keeping the rubber on the ground when there is so little grip...

  21. In a nutshell: flashing lights were legalised for pushbikes about 5 years ago. Other vehicles have to use static lights, may still only display white to the front and red to the rear (excepting indicators and reversing lights). Flashing ambers are allowed for approved categories of vehicle for safety reasons and only emergency vehicles can display any kind of blue light, flashing or not, or even if it works or not. All rules covering lights apply equally to reflectors.

    Vision is very much about interpolation from small numbers of significant artifacts, and heavily dependant upon previous experience. Babies actually start off with an excess of visual processing connections: as they grow older, those become fewer but more precise, allowing very rapid matching of shapes against previously identified templates. The trade-off for speed is sometimes accuracy - such as with colour correction, where the brain will perceive the item to be the colour it expects, rather than actually is, simply because the object match has actually been carried out primarily on shape.

    The problem with using attention-grabbing methods to be seen, is that - unless the method is unambiguous - it interferes with this process. The primary focus becomes the attention-grabber, rather than the object it is mounted on, which may or may be as easily identifiable. In context, a blue flashing light, for example, always and only equates to an emergency vehicle - hence, it gives an easy match. A patch of hi-vis does not necessarily, unless it also has a particularly distinctive shape: if it fails to match, then it is necessary to individuate the surroundings until something recognisable is obtained. In other words, it may succeed in attracting attention, but will then often hamper identification. The effect of that very much depends on whether the critical piece of information is that something is there, or what that something is, which is largely down to context.

    As far as motorcycles are concerned, I'm not aware of any visual aids that give a consistent net benefit. They all show some advantages within certain parameters, but carry disadvantages outside them. Silhouette recognition works against bright backgrounds, but not against dark. Colour and reflectivity does the reverse. Lights show up on the open road and merge into the background in already light-rich urban environments. Alternating between methods, depending on where you are, may actually work out but suffers from impracticality. Most people won't be stopping at the city outskirts to change from motorway fluorescents to urban black.

    In reality, you might as well pick what you're comfortable with and accept that, depending on the individual viewer's particular template for "motorcycle" they may or may not see and understand what they're looking at. Otherwise, you are just on the slippery slope towards abrogation of your own personal safety. Which is why I'll continue to rely on not relying on other motorists, and sticking to plain black.

    Plus, black IS cool.

  22. So, choose whatever conspicuity aids you feel are appropriate for you, but don't assume they will make you significantly safer. Ride as if they weren't there.

  23. I'm surprised that there has not been mention of the festoon arrays of high power LEDS now appearing somewhere near you on cages that render motorcycle lights as a visibility aid near to useless?

    I agree with your last comment!


Comment is free, according to C P Scott, so go for it. Word verification is turned off for the time being. Play nicely.

Related Posts Plugin for WordPress, Blogger...