TRANSPORT PROBLEMS

Te Awamutu Courier, Volume 60, Issue 4232, 17 January 1940, Page 4

TRANSPORT PROBLEMS

LESSENING RISKS OF ACCIDENTS •

LIGHTING ONE-WAY TRAFFIC ROADS

Whereas motor car headlamps try to reveal obstructions on the road by causing them to stand out as bright objects against a dark background, modern street lighting aims at making bright the road surface, against which objects on the roadway shall appear in silhouette. On ordinary roads, where traffic flows in hoth directions, lighting must be symmetrical to be equally suitable flor up and down traffic; but where vehicles are allowed to travel in one direction only, as in one-way roads, and those having two carriage ways separated by a strip of grass or a plantation, this is no longer necessary; and the lighting problem should therefore be simpler. In France experiments have been made in the lighting of one-way roads by means of lamps set only a feiw feet above the ground, pointing in the direction of traffic flow, and designed after the manner of floodlights, thus acting in the same manner as the motorist’s headlights, 'the results, however, wetre very disappointing, from the driver’s point of view, for, -though any objects on the road surface showed up clearly, the road surface itself seemed very badly lit; and with wet bituminous surfaces, a white keto or a lane of painted posts was necessary to enable motorists to keep on the ro..c. The fast driver on such a road felt safe only in the negative sense that he could see no obstruction ahead; and not because he could see that there was no obstruction. Further serious defects of this type of illumination were that t ie glare from the lamps was extremely 'unpleasant tc( pedestrians walking along the road or footpath against the traffic, and with double carriage ways a close fence or thick hedge was necessary between tracks, to prevent one from causing u~>on the other. And motorists who used rear-vision mirrors were apt to be dazzled by the glare of the road lamps behind them. The latest development for such iroads, now being tried in England, is to provide elevated lamps of the normal pattern, except for reflectors, designed to throw the whole of the light towards the approaching traffic, so that no lamp throws any light in the direction the traffic is moving. This means that every object on the road, whatever the tone of : ts colouring, shows up sharply in silhouette, as there is no light reflected from it towards the motorist to blur the contrast.

With light to be thrown in one direction only, the lamp housing is. capable of more exact design. The rear portion, is made of parabolic form, throwing a strong beam of

light about 25 degrees below the horizontal!, with appreciable vertical but little lateral, spread; while a projecting cowl reflects light on to the roadway nearer the post, giving a fair approximation to uniform intensity of reflection from the ro id surface up to a distance of 75 to 100 feet from the lamp post. ADJUSTING THE LAMPS The one-way direction of lighting also means that the lamps may much more readily be adjusted lor optimum service after erection, for there is no need to alter the position of the lamp with respect to th i reflectors, as- the whole housing maybe tilted or turned slightly. The ordinary lamp housing is naturally designed for use on level roads, and (this means that a lamp on the crest of an incline is apt to be unduly glaring to approaching drivers as they are looking up towards it, whereas the lamp at the bottom of a dip in road fails to throw its light as far as it should. If it is to serve for both directions of traffic the lamp as a whole cannot be adjusted to make conditions better <n one direction without making them worse in the other, so that any adjustments must be of the lamp inside the housing. And if provision is made for this there is always tno risk that the lamp will be wrongly positioned initially. It must simplify the task of the illumination in gineer considerably that the lamps may be adjusted from a tower waggon while actually burning. The general effect of this type of illumination is that, looking in the direction of traffic, the road appears well lit, whereas looking in the opposite direction, it seems almost unlit, the lamps themselves being barely visible. Thus at the point where a single road with ordinary lighting bifurcates to form a double carriageway road, there is not the slightest doubt in the motorist’s mind which road to take, as he naturally follows the one that he sees well lit.

This type of lighting does not overcome the problem of glare, the most difficult problem in the domain of highway lighting. A “cutoff” at about 75 degrees from the vertical will minimise trouble from this source, but will necessitate cl*>sc spacing of lamps if spelts of poor visibility are to be avoided. For use with normal spacings of 180 fe«it upwards, the housing is made fairly large, and provided with a diffusing glass front to diminish the intrinsic brilliance of the light; while the horizontal type of gas discharge lamp seems peculiarly adapted to this mode of street illumination.

Experimental results in England of the new system have been ve’-y promising. It is claimed that for an arte-ial double tralck road, where separate lighting is necessary for each carriageway, the .new plan. with 125 mercury vapour lamps will give illumination quite as good from the motorist point of view as with 400 watt lamps of the ordinary double-way type. For suburban double track roads with frequent intersecting streets, there would probably need to be some modification of this lighting at intersections unless it were required that cross traffic should come to a halt before entering.