HUTT ROAD DRIVING

Evening Post, Volume CXXVII, Issue 131, 6 June 1939, Page 10

HUTT ROAD DRIVING

SUPER-ELEVATION

FOR 45 M.P.H. SAFETY

Rain, heavy car traffic, and road ripping and reformation made a soupy, slushy mess of the Hutt Road during the' weekend and yesterday, but motorists are, with a few exceptions, accepting the surface mess as running unavoidably with heavy reconstruction work carried out during the- winter months. The Automobile Association has summed the position up in: "You can't have omelettes without breaking eggs," and has suggested that the permanent benefit of a first-class highway in a few months' time will more than make up for the inconvenience while the job is in hand.

The winter time-table was determined by the progress made in Ngahauranga Gorge, for not until April was this work so far ahead that plant could be freed for the Futt Road, and had a start not then been made at once the rebuilding of the road could not have been completed for the still heavier traffic of next spring and summer. Actually it is a toss up which is more intolerable —slush at intervals after rain in winter months or blinding dust throughout the, summer.

From the road construction point of view the wet conditions are all to the good, whereas dust is all to the bad, for the new methods of road consolidation require a fair amount of dampness to assist in the compacting of fills and metal, worked finer and finer, to form a mass almost as hard as concrete.

It is the present intention of the Main Highways Board not to relay a heavy bituminous pavement, but merely, to give the new road one or other of the highway surface treatments, the whole effectiveness of which depends upon the thoroughness of the compacting of the foundation. To this end graders and planers are steadily on the road, working down metal, brought from the last cuttings and excavations in Ngahauranga Gorge, to finer and finer (down to dust) sizes, to fill the underlying voids.

MANNERS WORSE THAN THE MUD

The continual grading and planing has a second purpose in maintaining a fair running • surf ace, having regard to the traffic volume of 10,000 cars, buses, and lorries daily, and of sweeping off traffic slush. The road surface is, in fact, several degrees of virtue ahead of the manners of a lot of drivers. For all the effect they have upon some drivers,, the warning and slow-down notices might as well not be there. The road has been good for thirty miles an hour and upwards; later it will be a 45-mile-an-hour road in comfort; just now 30 miles an hour over reconstructed lengths shows the completest disregard for others on the road. BANKING OF CORNERS. There is more criticism of the degree of banking on the sharper bends than there is of the state of the surface, and certainly after, the old camber —sloping definitely the wrong way on one or two bends —the tilting of the new surface is a surprise, but it is in accord with the general standard of super-elevation adopted by the Main Highways Board throughout New Zealand, worked out, literally to a decimal point, at so much elevation to so many chains of radius, to give maximum safety at a speed of 45 miles an hour.

There are bankings on the road over the Rimutaka Hill steeper than anything to be built upon the Hutt Road, but so far no one has found much fault with that contribution to road safety. On the Haywards-Pahautanui Road bends are super-elevated to a lesser standard, and fault has been found with them, because the outer elevation is below driving comfort.

The full engineering argument for super-elevation is complicated, but when all the forces are worked out and applied to banking they give a practically self-steering effect at 45 m.p.h., an inward steering effect (almost identically the same as the camber effect of a straight road) at a speed of 20 m.p.h.; and at speeds above 45 m.p.h. cars will still have to be held in to the curve, though the safety margin is much greater than upon a flat surface on the same curve.

. NOT INTENDED AS SPEEDWAY. I. The road is not being banked as a ■ high-class speedway; it is being banked Ito the specifications- recognised ' wherever highways are built or re- • built to give the maximum safety to - drivers who will drive at the speeds ' normal to modern cars, round about "45 m.p.h. It may be that in ten years' 1 time present ideas of safe speeds and economic speeds will have altered again, or it may be that a continuation of road accidents will result in drastic regulation of speed and driving habits, but the terrible total of deaths and injury from capsizings and over-runnings on bends determined the policy of the Main Highways Board in building roads as proof against this type of accident as possible. One reason why the banking appears so great is that the fills rise four and five feet above the cycle track level, whereas they do not show against a hillside, as on the Rimutaka Hill, and another is that the 50-foot width of the I road means that the outside edge is

lifted twice as high as the banking on most highway construction, where the running surface is 24 feet or so. No highway authority, city council, or county council is building fiat roads round curves any more. The banking on the new Hutt Road is simply in accord with practice wherever motor traffic runs, a recognition that speeds outside built-up areas do average about 45 miles an hour, and is some considerable, but not a complete, protection for the minority who will-pile on speed, whatever ihe road provision.