MODERN TRAFFIC REQUIREMENTS

Hokitika Guardian, 11 August 1930, Page 2

MODERN TRAFFIC REQUIREMENTS

SAFETY STANDARDS. SPECIFICATIONS FOR MAIN - HIGHWAYS. WELLINGTON, August 8. / . Though the Main . Highways Board recent bulletin of road specifications contains matter of a purely technical nature it makes interesting reading lor motorists, since it .clearly outlines the standard to which our main highways should be constructed. Piacticnity everyone contributes to the road funds, and it is with the object of 1 showing what we may expect to get <for our money that this review of. the bulletin is being made. Increasing speed of motor vehicles accompanied by a greater density oi traffic, necessitates a more careful regard for higher construction standards. Those which are laid down by the board are designed to secure greater safety for the road user under modern conditions. On all classes of roads provision is suggested in the stand, l i d specifications for generous shoulders, permitting parking of cars without unduly restricting the flow of traffic. 11l difficult country, where a wary, eye must be given to, earthw,ork quantities, the provision of a shoulder width greater than three feet would cel thinly result in prohibitive construction costs, but on first-class roads the standard specification suggests that if the surfacing is IS to 20 feet, the total foi illa-

tion should be 24 to 30 feet. The recommended minimum radius of curvature of six chains should prove no serious hindrance to road designers except in a few extreme conditions. There is a section of the Wellingthiir Auckland niain highway between Shannon and Palmerston North vvlieie the motorist lias to round curves of a radius of a chain and even less. This is admittedly a had. .section, hut the illustration serves to show how standards have progressed. Curves, have to be super-elevated according to a scale which has been previously explained, the factors involved in deciding the degree of super-eleva-tion ;being speed and the radius of ■ coirvat'ure. ~ The graphs shoiy—a learning’ to speedsters—that the salfetvmargin decreases more irapidly . than the; speed increases. !MjjU'... A further refinement on curves'; included in thes standard specifications is the iprjvijsio.n joL,-additional fifidth on'the! inside of .curves’up to 10 chains radius. This‘permits off. passing y iat .higher speeds, with a safe cleuranhe) between vehicles, and also allows! for’ ■ the fact that the rear wheels do not follow exactly the path of the frOfit wheels artrillid a curve, hut run inside them. ; Both super-elevation and additional vi’ideriirig. of Curves Will be iritroy duced gradually, so that no sudden change from the normal section will be experienced when driving. VISIBILITY STANDARD. .. ~

The recommended minimum visibility of 300 feet on first-class highways is somewhat generous, hut it must be remembered that opposing traffic travelling at 30 miles an hour would meet at this distance in a, shade over three, seconds. In hilly country some difficulty might he experienced in obtaining a clear sight over the recommended distance, but this can be overcome by “benching,” which means cutting back a step in the batter over which drivers may see the requisite distance ahead. Probably the designers have forgotten the “baby” car when they recommend four feet for the height of tlie step. EASY GRADIENTS. No complaint can be found with the recommended gradients, which are well within the scope of all motor vehicles now using the roads. A question left untouched, however, is the bituminous paving of grades. It' is well known that this tpye of paving becomes slippery in wet weather and treacherous when coated with frost. The resulting lack of control might have serious consequences, and there was. a .recent instance on the Hutt Road, Wellington, when half a dozen motorists encountered trouble at the same spot, immediately they ran on to the bitumen where it was frosted. 1

’''-A- noticeable feature of our highway system at present ■is the variation of camber experienced on the' same class of road, as one travels through various country sections and highway districts The recently published Bulletin specifies within narrow limits the camber to be given to each class of road, and it is to he hoped that these standards will be rigidly enforced! Nothing is more annoying to the motorist than to be driving on a road where he seems in imminent danger of sliding into the water-table. The cambers recommended are all moderate, hut sufficient to provide efficient cross drainage. Stress is laid on the introduction, at all changes of grade, of vertical curves designed to “ease the bump.” It is pointed out that not only are these a much appreciated refinement, but that they are a most effective tool in the hands of the engineer, enabling him to closely follow the original ground level and cut earthwork down to a minimum, while still providing a firstclass road. The Bulletin contains a complete .set of /typical •oross-sqtetion for waterhound macadam etc., and for each type there is a comprehensive specification. There can he no doubt that this Bulletin contains data representative of the highest standard of highway construction. Its general circulation will ensure uniformity in our roads, though the task of bringing them up to the same standard must necessarily bo accompanied gradually. j