C. RAILWAY CONSTRUCTION (cont.)
The practice with regard to the height of platforms above the rails has varied considerably, the tendency being to raise them much higher than usual at first; 3 feet may be stated as the limit in this respect. Too much attention cannot be given to the necessity for obtaining the greatest possible width of platform. Where the platform is used on one side only, the width ought never to be less than 20 feet; and when both sides are required 30, or even 40, should be allowed. The best mode of constructing the platform is undoubtedly with stone slabs laid hollow upon longitudinal walls, so as to admit of carrying beneath it the water and gas pipes, telegraph or signal wires, and the general drainage, with free access to each. Cutting out for turn-tables and openings for cross lines of rails are frequently inevitable difficulties which have given rise to various ingenious contrivances, as shifting-stages, drawbridges, &c. By far the best substitute for the turn-table yet introduced is the traverser. If well made and carefully worked and attended to, the shifting of carriages from line to line can be performed without extra manual labour or interference either with the rails or the platforms. The other objection is best met by the use of easy inclines, with crossings on the rail-level. Where the platforms do not exceed 2 feet in height and the surface is smooth, gradients of 1 in 10 are not too step for luggage-barrows, nor are they dangerous in a crowd.
The earlier terminal railway stations were designed either with intermediate columns supporting the roof or with brick walls, varying in number of spans from two to five or six. It often happens that in the course of a few years such stations have to be remodelled to meet the constantly increasing traffic; and great difficulties are occasionally met with in the rearrangement of platforms which are wasted where lines of rails have been laid, whilst rails are wasted where platforms are placed, and where columns interfere. To allow engines and carriages to pass from one line of rails to another at the shortest possible intervals it becomes necessary to have diagonal crossings from one part of the station to another in many directions, while at the same time the free movements of passengers and luggage on the platforms must not be impeded. Thus there arose a system, originated, it is believed, in the great Continental termini, of constructing roofs in two spans, one covering the up lines of rails and the other the down line. Kings Cross passenger station is an example of this kind. The principle of wide spans for the roofs of railway stations, clear of intermediate walls of columns, was adopted in England probably for the first time in 1848-49, in covering Lime Street station, Liverpool, on the London and North-Western Railway, by one span of 153 1/2 feet. The extreme length of the roof was 374 feet. The new Lime Street station, it may be added, is covered by a roof of one span of 212 feet. Tythebarn Street station, Liverpool, on the Lancashire and Yorkshire Railway, is covered by a roof in one span of 136 feet; there, as the traffic increased, the lines and platforms were changed so as admit of treble the quantity of traffic being conducted, which would have been impossible if the roof had been built with sectional spans and columns. It is averred that the railway company has been repaid the excessive cost of the single-span roof many times over in economy of working. The next single-span roof on a large scale appears to have been that of 212 feet covering the New Street station, Birmingham, in which five lines of way, belonging to different companiesthe London and North-Western and othersmeet and concentrate passenger and goods traffic of every description. The roof was 840 feet in length, with trusses or principals placed at intervals of 24 feet. The principal consists of one arched plate-iron girder 15 inches deep, having a rise of 45 1/2 feet at the centre. The ends of the arch are tied by a round tiebar 4 inches in diameter, from which the arch is strutted at intervals. This is said to cover the largest area of any station in England.
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