What might have proved a source of great trouble and expense—water—has fortunately not as yet on any one occasion presented itself in a manner to cause alarm or even uneasiness. We need not therefore refer to this subject in any detail, but before proceeding to as important an element as any with which the tunnel is encompassed—cost—we had better state that the arch of the tunnel is a semicircle 25 feet 3½ inches at its base, 26 feet 3 at its broadest part, and 24 feet 7 inches high. (See diagram.)
Captain Tyler in his report of 1866, sets down the total cost of the tunnel and its 34½ miles of approaches at £5,400,000, or £128,500 per mile. Now we know that up to the present time each metre of tunnel excavated and lined (for it is to be lined throughout from stone quarried near to each entrance, with an occasional introduction of brickwork) costs 7,000 francs, or £280. This would bring its total cost exclusive of permanent way, which would be, say £30,000, to £3,421,600, but we believe that the farther the tunnel is penetrated, the expenses will increase rather in geometrical than arithmetical proportion, and that the average cost of the tunnel will not be 7,000 francs or £280 “_per metre courant_,” but 10,000 francs or £400. If this be so, the cost of the tunnel, without permanent way, would be £5,188,000. To this sum has to be added the cost of the 34½ miles of approaches. The nature and the probable cost of the works can be appreciated from the fact that they are now about to be let, and the contract time for their completion is to be four years and a-half from the date of their commencement. These 34½ miles of double railway cannot be estimated at less than £60,000 a mile or £2,070,000, making the total cost of the tunnel and of the railways which connect it with the railways of France to the north, and with those of Italy to the south, £7,258,000, or at the rate of £172,800 per mile. Possibly, if the construction were in the hands of a railway company instead of those of two governments, a saving of a million or so might be effected, but in any case the cost would be upwards of £6,000,000, or nearly £142,850 a mile.
In connection with the subject of cost, a calculation of Captain Tyler’s gives the following results. The difference, says the Captain, of elevation between the outer summit of the Mont Cenis Pass and the summit of the railway through the tunnel is 2,520 feet. The excess of working expenses in consequence of this difference of height, estimated on a traffic ten times as great as that which passed over the Mont Cenis in 1865, and the cost of traction per horse power and per hour being taken at 2¼d. (the cost on the Sœmmering and the Giovi), an additional capital of £650,000, or £13,000 a mile, with interest taken at 6 per cent., is represented. If then £13,000 a mile be added to the £21,000 actual cost per mile of a permanent Alpine railway, the total cost of a railway _on_ the mountain becomes, for the purposes of comparison, £34,000 a mile, as against whatever may be the cost per mile for the Tunnel Railway and its approaches. If they cost £142,850 a mile, the comparison will be as 31 to 142; but, if, as we believe, the cost will be £172,800, then the proportion will be at 31 to 172.