The number of passengers carried by the Interboro Lines during the fiscal year 1921 was 1,013,678,831. This figure represents 2,773,479 passengers per mile of track. In the main 4-track subway 10-car express trains are operated during rush hour periods on minimum headways of 108 seconds. _Power Supply_ The power generating equipment of the Interborough includes briefly the following: ════════════════════════════════╤═══════════ 59th St. Power Station │ Total Kw. ────────────────────────────────┼─────────── Turbo-Generators 3-30,000 kw.│ 90,000 Compound Units 5-15,000 kw.│ 75,000 Engine-driven Units 4- 7,500 kw.│ 30,000 ├─────────── Total │195,000 Kw. ────────────────────────────────┴─────────── ════════════════════════════════╤═══════════ 74th St. Power Station │ Total Kw. ────────────────────────────────┼─────────── Turbo-Generator 1-60,000 kw.│ 60,000 Turbo-Generators 3-30,000 kw.│ 90,000 Turbo-Generator 1- 7,500 kw.│ 7,500 Engine-driven 3- 7,500 kw.│ 22,500 ├─────────── Total │180,000 Kw. ────────────────────────────────┴─────────── Power is generated 11,000 volts three-phase 25 cycles and transmitted principally underground at 11,000 and 19,000 volts. The total energy generated in the two main sections at 59th St. and 74th St. for the year 1921 was 830,000,000 kw-hrs. _Substations_ For supplying 625-volt direct current to the rapid transit lines, there are a total of 25 substations containing 129 synchronous converters aggregating 283,000 kw. _Distribution_ Propulsion current is delivered to trains through an unprotected over-running third rail weighing, in the old subway 75 lbs. per yard, on the elevated 100 lbs., and in the new subway 150 lbs. per yard. _Rolling Stock_ The motor car equipment on the Manhattan Elevated lines includes over 800 cars which have been in operation since 1902-4 with GE-66 motors and Type M control. These cars after 20 years of hard service are referred to as the “back-bone of the system.” Frequent additions have been made to elevated and subway equipment so that the total rolling stock at the end of the fiscal year 1921 was as follows: INTERBOROUGH RAPID TRANSIT ROLLING STOCK EQUIPMENT