Engineering Wonders of the World
Volume I

THE NEW YORK SUBWAY. 351 Fig. 15.—ONE OF THE LAMP SIGNALS WHICH PRO- TECT THE EXPRESS TRACKS OF THE SUBWAY. The upper lamp is the “home” signal, showing red for “danger” and green for “clear.” The lower lamp is the “distant” signal, showing yellow for “caution” and green for “clear.” Automatic stop lever for applying brakes appears at right of the track. rely on seeing the train ahead, and frequent collisions would be inevitable if automatic lamp-signals were not provided. These lamps, set in narrow pedestals at the right of the track (Fig. 15), show red (“danger”) whenever a train is close ahead, but as the train draws ahead to a safe distance the red cover-glass is replaced by a green one. Com- pressed air, controlled by electro-magnets, moves the glass slides. The magnets are energized by an electric current impressed on the track rails some distance ahead ; a train on this section of the track short-circuits the signalling current so that the magnet drops, the compressed air in the cylinder is released, and the slide drops to “ danger ” position. This system works with marvellously few misses,” according to the records of opera- tion. Its performance is the more noteworthy because the signalling current is alternating current; the magnets, etc., had to be so arranged that they would not respond to the return power current in the track rail (which is direct or continuous current), but only to the alternating signal current. But safety is really attained only if the signals are implicitly obeyed. To ensure the motorman’s obedience, the Subway is fitted with “ automatic stops.” When any signal is at “ danger ” a small metal arm near by projects above the track, in position to strike a valve-handle on the air-brake pipe of a passing train. Thus, if a train runs by a signal set at “ danger,” its brakes will be applied automatically. When the signal is green (“ clear ”) this arm is folded down out of the way by a lever connected to the signal mechanism. Electric current for running the trains is generated in an immense power-house on the bank of the Hudson at 59th Street. Here stand nine 10,000 horse-power compound engines, fed by fifty- Power-house. two large boilers, and driving each an 11,000- volt three-phase alternating-current gener- ator (Fig. 16). The current which they produce goes by underground cables to several sub-stations, where it is converted to direct current of the working voltage, 625 volts. This is led to the third rail of the track by copper feeder-cables. The cars (Fig. 17) are notable for strength, and for the fact that many of them are built wholly of metal. They are 51 feet long, 9 feet wide, and 12 feet high over all. Steel frame, steel and aluminium sheet, asbestos, etc., displace all combustible material except the wicker seat surfacing and a wooden floor grid. By this and similar precautions it is hoped to render impossible an accident like the holo- caust on the Paris “ Métropolitain ” subway a few years ago.