The views of a DRL user - why they think they are safer

Views on DRL from:

Last updated

30 June 2008

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Mike Arthur has kindly allowed an edited version of a posting to the Association of British Driver forum to be reproduced to give some balance in favour of DRL.

Basics:

Lights (static & moving) serve 2 purposes: a) indicating the position of an object (generally applied at night / poor visibility, but including clear daylight); b) illuminating the path ahead (applied exclusively at night). We are talking about a) only.

1) On a clear night lights for a) can be of almost trivial power / brightness (e.g. the match / cigarette on a blacked out ship in a convoy, which really can be seen, by a dark adapted eye, from far away). Presumably nobody contests that parking lights on cars, navigation lights on ships and aircraft, & lighthouses, really do allow an object to be seen much sooner than otherwise, and that there are no significant adverse consequences to such lights (they do not dazzle, mislead etc)? Certainly, their universal employment, over centuries, suggests that they have *proved* (by natural selection / evolution in action) to be, in sum (i.e. allowing for the odd case where they might cause an accident), beneficial.

2) In poor (fog, heavy snow / rain) daylight conditions, it is a matter of simple observation that parking lights on road vehicles are inadequate at giving sufficient time warning of the positions of vehicles, and so higher intensity lights must be used (dipped beams at front, high intensity rear fog lights). Is there any contest that in poor daylight conditions correctly used higher intensity lights are, in sum, of benefit to safety?

3) There is then the case of use of lights in clear daylight. Everyday observation suggests that side (parking) lights cannot then be seen beyond a tiny distance (neither do they cause any distraction / dazzle). Everyday observation shows that dipped headlights can be seen from a considerable distance, and aid the detection of a 'target' earlier than otherwise (albeit, at the expense of unlit targets?).  Trevor Magner of the BMF (citing 25 years' experience of riding motorcycles) has raised some alleged difficulties with use of such lights in clear daylight. I reply, citing 35 years' experience of driving cars, and (comparatively, very limited) experience of manoeuvring dinghies, fixed wing gliders, hang gliders, and powered aircraft in 2D & 3D proximity to other such vehicles; the powered aircraft was as a student doing part time very basic flying training with the RAF - who are extremely safety conscious, and provided specific lectures on visual difficulties. In that experience, and driving  on a clear afternoon yesterday on a dual carriageway / motorway, where cars and motorbikes passed in both directions.

a) I have never experienced day dazzle, from in front or behind (yesterday I stared at headlights in front & behind, without the slightest twinge of reaction). This is hardly surprising - the eye is adapted to full daylight and the additional stimulus from a dipped headlight is negligible (if I recall correctly, the eye's response is given by the Weber-Fechner Law: R = K log A2/log A1, A1 = normal daylight intensity, A2 = A1 + headlights; because logs are taken, headlights would have to have a colossal intensity to have any significant perceived effect). If dipped headlights are causing dazzle sufficient enough to cause accidents in bright daylight then they must be causing a holocaust of accidents when the eye is dark adapted (in poor daylight / at night). If they caused dazzle in daylight then people would be flipping down sun visors, putting on dark glasses, dipping the rear view mirror; I've never done any of these - has anyone?

b) On any normal road I don't see headlights going up and down according to bumps - it takes something speed bump sized to have that effect. The characteristics of a headlight flash (off, on, off) are completely different from those of an 'on' headlight going over a bump - which creates only a very slight, & comparatively gradual,  apparent change in intensity. The presence of a bump can be obvious - because you have just passed over it, or because a succession of cars from the opposite direction have passed over it. Non-deliberate bumps are also randomly distributed, they have no correlation with hazards (such as junctions), and, therefore, mistaking the effect of one for a headlight flash would mostly lead to no action by the perceiver (other than to think 'why on earth did he flash me - must have been a mistake).

c) I do not see headlights (car or motorcycle) obscuring indicator lights; if they did then it would indicate poor design / relative placement of the lights. Furthermore, most of the beneficiaries (maybe two-thirds?) of signalling are behind a signalling vehicle, and therefore unaffected by its headlight. If this obscuring was occurring in clear daylight then, again, it should be creating a holocaust of accidents when headlights are being used in poor daylight / at night.

d) i) At any significant distance vehicles are perceived as 2D (rather than 3D) objects. I presume the ease of recognising them is linearly proportional to their frontal area (rather than obeying a 'power' law, such as the WF 'log' law). It is then no defect in the attention of a car driver that leads to difficulties in spotting motorcycles - it is because they have about a third the frontal area of a car, and, can only be noticed at one third the distance a car could be noticed - other conditions being equal, nothing can change this. Even within the distance for perception of a motorcycle, they will presumably be only one third as noticeable as a car.

ii) Cars can be highly coloured, but motor cycles are often drab - a significant part of their frontal area is black tyre, often surmounted by a black clad figure (one such overtook me yesterday - very sensibly he had his headlight on). I don't think it can be contested that colouring & brightness affect the ease of detection of objects (does Trevor do so?). Insurance statistics show that the accident rates do differ for different colours of cars (yellow being the safest). Bright colours are universally adopted to make vehicles conspicuous (e.g. ground vehicles round aircraft, day-glo colours on aircraft & road vehicles). Reflectors are used on children's equipment / clothing, survival clothing, road hazards, cats eyes, & elsewhere, without leading to dazzle / distraction. Military uniforms have gone from red, to khaki, to camouflaged to have the opposite effect - to render inconspicuous. Animals have colour schemes to render inconspicuous (or, sometimes, conspicuous for mating). These human & animal colour schemes are the result of natural selection / evolution over centuries - they work / are proved.

iii) Summarising i) & ii): motorcycles are a classic 'stealth' target (in terms of appearance (which often amounts to camouflage) & image size). The BMF argument seems to be that this is good (it makes other drivers work harder at detection); taken to its logical conclusion, this argument would mean that motorcyclists, as other vehicles, should render themselves as inconspicuous as possible (there are only 2 choices - make as conspicuous as possible, or as inconspicuous as possible - which to choose, & why?) Daytime headlights on a motorcycle render it, as other vehicles, more conspicuous - they are just an extension of bright colours & reflective items.

e) I have never had any experience of daytime lights obscuring pedestrians, or unlit objects; since the eye reacts minimally to daytime lights I find it impossible to imagine any difficulty here. If there were difficulties in daylight then, again, there would be a mass of such accidents in poor visibility / at night. My experience as a driver and pedestrian in Scandinavia was that day lights aided perception of hazards (e.g. they immediately show which cars in a crowded scene are moving, or are likely to move).

f) There is an argument that daylights lead to focussing on them (rendering a vehicle almost a point/1D), & obscuring aspects of a vehicle's behaviour. I have never experienced this. You also have to notice a vehicle before you start analysing its behaviour. Lights lead to early recognition, giving more time for analysis. Flashing (strobe / anti-collision) lights on aircraft (&, now, agricultural tractors) serve the same purpose by day as well as night - they indicate presence from a long distance away, before shape or navigation lights are discernible; they are poor indicators of manoeuvres, but do mean you have a target to monitor for the better indicators of manoeuvres. As the 1D target moves nearer it inevitably turns to 2D then, 3D.

g) There is an argument that a lit vehicle receives an unwarranted amount of attention. Again I have not experienced this - one constantly scans front & back, &, if anything, more quickly dismisses an obvious vehicle & searches for what one may have missed. If all vehicles were lit than this argument would disappear.

i) There is comment that a study of the Scandinavian results did not show an increase in safety from adopting day running lights. Subject to this being an accurate report of the study, and it not having been superseded by a later one, than I think one has to accept that. However, the finding seems very surprising, & it would be very interesting to know which actual factors (increased risk taking?, as several have suggested) countervailed the expected success of day lights in making vehicles more conspicuous / safer. Presumably the report must have suggested answers. But, 'not making safer' is not the same as 'making unsafer', so there appears to be no harm in using day running lights.

Mike Arthur <Mike.Arthur@newscientist.net>

Consultant Geophysicist: B.Sc. (Geology, 1970); M.Sc., D.I.C. (Geophysics, 1971); M.Sc. (Reservoir Evaluation & Management (Petroleum Geoengineering), 1994).

DUNFERMLINE, Fife, United Kingdom