The power for the early elevated lines was derived from engine-driven direct-current power plants all of which have since become obsolete. All power, therefore, is supplied from the network of the Commonwealth Edison Co., which maintains an ample reserve to supply all needs. While a large percentage of the power now being purchased is generated at 25 cycles, the policy of the Power Co. on all new equipment is to specify 60 cycles. _Substations_ 12 out of the 32 substations supplying the various traction systems are owned and operated by the Commonwealth Edison Co. and only 60-cycle generating equipment is installed when adding to their present capacity. The several substations contain synchronous converter units ranging in size from 1000 to 4000 kw. each. The preferred size for new 60-cycle substations is the 3000-kw. unit of which there are now five in service. The following table shows the ownership and gross capacity of the substation equipment for all of the Chicago lines. It is not possible on account of the diversity of feeding arrangement to designate any particular stations as belonging exclusively to the elevated lines. SUBSTATIONS—CHICAGO TRACTION SYSTEMS ═════════════════════════════╤════════╤════════╤════════ Operating Co. │ No. │ No. │ Total │Stations│ Units │Capacity ─────────────────────────────┼────────┼────────┼──────── Chicago Railways Co. │ 10│ 32│ 80,000 Chicago City Railway │ 7│ 26│ 53,400 Calumet & So. Chicago Railway│ 3│ 9│ 9,000 Commonwealth Edison Co. │ 12│ 33│ 105,000 Elevated R. R. │ 3│ 8│ 9,000 ├────────┼────────┼──────── Totals │ 35│ 108│ 256,400 ─────────────────────────────┴────────┴────────┴──────── [Illustration: LATEST TYPE OF 3000-KW., 60-CYCLE SYNCHRONOUS CONVERTERS INSTALLED BY COMMONWEALTH EDISON COMPANY, FOR CHICAGO SURFACE AND ELEVATED LINES] The Northwestern Elevated R. R. has on order a complete 2000-kw. automatic substation from the General Electric Co. to be installed at Buena Park. This is the first application of the automatic to Metropolitan Rapid Transit service. _Distribution_ Energy for elevated train operation is fed to the third-rail shoes at 600 volts. The third rail is of the top contact unprotected A.S.C.E. rail varying in size from 40 to 80 lb. _Rolling Stock_ The rolling stock equipment includes a total of 1008 two-motor cars weighing from 22 to 35 tons each, the latter figure representing the more recent types of cars. The distribution of these cars among the four divisions is as follows: