Railway Grade Problem

Progress, Volume X, Issue 8, 1 April 1915, Page 277

Railway Grade Problem

The Routes out of Wellington. Engineers report on

alternative projects

Wellington provides the railway engineer with a fairly stiff problem. Its splendid deep water harbour is surrounded on all sides by steep hills, and even the promising outlet via the Hutt Valley eventually ends in a sharp rise over the Eimutaka, with

its gradient on the far side of one in fifteen. The rapid growth of traffic following the opening of the North Island Main Trunk route to Auckland, and the diversion of the Hawke's Bay traffic through the Manawatu has piled a heavy load upon the section between Wellington and Palmerston North, and the day is not far distant when some relief by way of duplications, or the building of an alternative line for part of the distance, will have to be faced. Between Wellington and Paekakariki the load of trains is governed by a grade of 1 in 35 out of Wellington serious limitation but beyond Paekakariki, the gradients are easy, the ruling grade being one in 100. South bound trains from Paekakariki have to climb a grade of 1 in 53 to reach Johnsonville, after which the grade is favourable. Sev-

oral alternative routes have been suggested to overcome the rise to Johnsonville, but a report furnished by the Chief Engineer of the Public Works Department (Mr. R. W. Holmes) shows that, after all, the existing line affords the best grade.

Mr. Holmes’ report to the Minister of Public Works is accompanied by a plan on which is outlined the existing railway, and the suggested alternatives. This we reproduce on the opposite page. Mr. Holmes states:— Prior to the construction of the present railway the whole of the country between Wellington and Waikanae was explored, and several trial lines were surveyed. On the small scale tracing attached hereto are indicated the existing railway between Wellington and the Upper Hutt, also that between Wellington and Waikanae, and lines of surveys made and marked respectively Nos. 1,2, 3, and 4, part of No. 4 being ultimately adopted for the present railway.

A glance at the plan will show that the construced line is by far the shortest and most direct route between Wellington and Waikanae. The next shorter is probably that marked No. 1, which leaves the Upper Hutt and joins in with the present line at Waikanae. This line, however, has to climb over a saddle about 1,400 feet above sea level, which height, however, is reduced by tunnelling to about 1,000 feet. Johnsonville, the highest point on the existing line, is about 500 feet above sea level. In addition to No. 1 route having to climb to the height mentioned, the plans show that the work of construction will be extremely heavy, and that very great difficulty would be experienced in locating a line with anything like the flat curvature necessary, and which can be obtained by modifications of the existing line. No. 3 route, which extends from Hayward’s on the Wellington-Hutt line to Pahautanui, is a practicable line, but as originally surveyed from Pahautanui northwards is, through passing over the Packakariki Hill, impracticable north of Pahautanui. To avoid the Paekakariki Hill this route wiuld have to follow the dotted line, joining the existing line at Plimmerton. A glance at the plan will show that this route is so much longer than the existing line as to be not worthy of consideration. Along the existing line between Wellington and Paekakariki there are two hills, Johnsonville being

at the summit of one and Pukerua at the summit of

the other. This latter hill can be easily avoided by constructing the line round the sea-coast as indicated by crosses on the plan. This line would be longer, would be somewhat difficult to construct in a few places, and would be subjected to the corrosive action of the sea-spray as regards the maintenance of the rails. This line, although suffering from the disadvantages mentioned, would have a perfectly level grade, over which traffic could be handled quickly and with very little expense as regards locomotive charges. The present line between Wellington and Porirua can only be improved by lowering the summit level at Johnsonville by tunnelling. It is probable, however, that to effect any marked improvement and one worth consideration it will be necessary to adopt a tunnel not less than two miles in length. To construct this tunnel and to improve the gradients on each side would probably cost £350,000, the interest on which alone would amount to £14,000 per annum, or far more than assistant engines cost to work the traffic over the hill. On the question of haulage, the construction of such a deviation or any of the deviations quoted between Hayward’s and the Upper Hutt cannot be considered as businesslike propositions. The only possible excuse for considering an improvement of the line will be when speed has to be considered, and it is proved that the traffic cannot be worked with sufficient rapidity between Tawa Flat and Wellington.