The bringing of the subway close to the sur face necessitated carrying surface traffic during construction, usually by means of temporary bridges, and the permanent readjustment of sub surface structures. In the matter of sewerage, this readjusting was done by substituting for a single sewer in the centre of the street, two smaller sewers, one on each side, and by car rying cross sewers in iron pipes beneath the sub way at suitable points. In the matter of water and gas mains, pneumatic tubes and electric conduits, a complete rearrangement was adopted by leaving the smaller ones above the roof and placing the larger ones at the sides. A satis factory arrangement of these sub-surface struc tures was a work of great difficulty and ex pense.
In general the design of this old subway proved very satisfactory, yet in operation cer tain defects developed which were avoided by the engineers of the Dual System. Many of the stations of the old subway were built on curves. A considerable space was left between the car and station platform on these curves which proved a source of constant danger in rush hours and were the cause of not a few fatalities. Moreover, it is necessary to slow down sooner when approaching a curved plat form than a straight one, and in the rush hours, when trains are operated on short head ways this slow-down tends to cause congestion at those points of the line where there are curved platforms. The ventilation of the old subway was defective in that all four tracks were placed in one tunnel. The passage of a train there stirred the air, but did not renew it, since the air escaped to the side of the train and was not propelled ahead of it to the ex hausts. The new subways have a partition be tween each pair of tracks, so that there is really a tunnel for trains going in the same direction and one for those going in the op posite direction. Excessive heat developed in the old subway in the summer. This is due to friction of wheels, brakes, etc., and to the op eration of the car motors. The old subway was waterproofed all the way around—underneath, at the sides and overhead—and this waterproof ing, while most effectively keeping water out, prevents radiation and confines the heat within the tunnel, which is augmented by each passing train. Less waterproofing characterizes all recent subway construction.
On the old New York subway there are two classes of stations, one for local, the other for express trains. The platforms of the local sta
tions are on the outside of the outer pair of tracks, and are reached directly from the street surface, and at these points there is no con nection with the express (the central) tracks. At the express stations, the local (outer) tracks are curved outward so as to permit the con struction of an island platform between each local and express track. The station stairways in this case are located as before, on the side walks and lead to a ticket office beneath the street, from which there leads a bridge passing over the tracks and connected with both the island platforms by stairs. The more import ant stations cover two streets and have numerous exits and entrances. Straight plat forms exclusively are built on the new lines. The openings at subway stations were assumed to be sufficient to provide for ventilation of the subways; but this proved an error, and numer ous openings were added, as well as blowers at congested points. See New YORK CITY.
The cost of constructing subways is very great. In this respect, the New York subway, being the largest and most complete as yet constructed, has cost (including all work in hand estimated complete) about $400,000,000. This figure includes many miles of surface and elevated tracks allied with the system, and the usual proportion of ((water)) for financing the proposition. The most expensive four-track section cost at the rate of nearly $5,000,000 per mile. In Boston 1.7 miles of subway, a part of which was four-track, cost $4,250,000. In Paris the cost averages for two-track subway about $850,000 per mile, while in London tubu lar railways cost about $1,500,000 per mile, without equipment in all cases.
Operation.— As stated above, the first sub ways built in London were worked by steam locomotives. All lines subsequently constructed, except one in Glasgow, have been and are oper ated by electricity. In the exception above noted a cable was the source of power. As the orig inal lines are now being converted to electrical operation, it has become the sole power now in use. The power is generated in central sta tions by direct driven generators, usually of large size. The largest central station so far constructed is the station built to operate the subway in New York. In this station there are eight units, which have nominally 5,000 kilowatt capacity each, and which, together with sub sidiary engines, represent a total of 132,000 horse power.