The Growth of the Track Circuit
Unfortunately there exists little or no data regarding the mileage of track circuits installed from the time the first installation was made by Dr. Robinson at Kinzua, Pa., and Irvineton up to about 1905. During the period between January 1, 1905, and September 30, 1906, the total automatic block signal mileage installed was 1,710.6, which brought the total up to 6,826.9 for the United States. Between September 30, 1906, and January 1, 1908, 3,976.1 miles of automatic signals were installed, which increased the above total to 10,803.0 miles.
The Block Signal and Train Control Board, seeing the need for accurate data in the signal field, started the tabulation of such statistics when it compiled and issued Block Signal Statistics as of January 1, 1908. After this board went out of existence, the Bureau of Safety of the Interstate Commerce Commission continued the collection and publication of these data yearly. Perhaps no better word picture can be given of what Dr. Robinson's invention has meant to the railroads than to present the story in the form of a table showing the miles of road and the track equipped with the track circuit since January 1, 1908. In addition to the table, the accompanying chart presents the information in a graphical form.
Progress Chart of Automatic Signal Installations
Since January 1, 1908.
Track Circuit Mileage for Automatic and Controlled Manual Signals in the United States as Taken from I.C.C. Reports
| Automatic | Controlled Manual | |||||
| Miles of Road | Miles of Track | Miles of Road | Miles of Track | |||
| Track Circuits at Station | Continuous Track Circuits | Track Circuits at Station | Continuous Track Circuits | |||
| January 1, 1908 | 10,819.3 | 18,534.1 | 726.7 | 212.0 | 2118.0 | 410.8 |
| January 1, 1909 | 12,174.3 | 20,590.9 | 407.6 | 572.2 | 978.0 | 1413.0 |
| January 1, 1910 | 14,238.9 | 23,771.3 | 385.8 | 491.5 | 953.5 | 1371.3 |
| January 1, 1911 | 17,709.8 | 29,151.6 | 483.9 | 439.4 | 1119.3 | 739.9 |
| January 1, 1912 | 20,300.0 | 33,343.8 | 402.0 | 295.9 | 955.6 | 496.0 |
| January 1, 1913 | 22,196.6 | 36,873.0 | 370.2 | 228.3 | 868.9 | 380.3 |
| January 1, 1914 | 26,569.3 | 44,461.2 | 275.7 | 180.3 | 625.3 | 281.6 |
| January 1, 1915 | 29,863.5 | 49,442.1 | 250.5 | 145.1 | 549.3 | 185.7 |
| January 1, 1916 | 30,942.5 | 51,119.7 | 255.1 | 125.1 | 549.6 | 179.3 |
| January 1, 1917 | 32,954.6 | 53,799.8 | 230.3 | 132.0 | 524.8 | 155.5 |
| January 1, 1918 | 35,193.1 | 57,083.6 | 208.1 | 131.2 | 451.6 | 154.8 |
| January 1, 1919 | 36,989.4 | 59,458.2 | 221.2 | 256.9 | 483.8 | 441.2 |
| January 1, 1920 | 37,968.8 | 60,992.3 | 196.3 | 129.2 | 413.3 | 151.4 |
| January 1, 1921 | 38,543.9 | 61,744.5 | 206.8 | 125.7 | 422.6 | 166.4 |
The first yearly report of the Bureau of Safety, I.C.C., on block signals to contain information as to the miles of road and miles of track on which alternating current track circuits were installed, was that issued as of January 1, 1914. Data taken from that report up to the last one issued is presented in the table below.
Alternating Current Track Circuit Mileage
| Miles of Road | Miles of Track | |
| January 1, 1914 | 3,289.2 | 4,144.6 |
| January 1, 1915 | 2,728.2 | 5,814.9 |
| January 1, 1916 | 3,186.7 | 6,679.0 |
| January 1, 1917 | 3,336.2 | 6,823.6 |
| January 1, 1918 | 3,748.0 | 7,530.1 |
| January 1, 1919 | 4,496.6 | 8,620.2 |
| January 1, 1920 | 4,676.5 | 9,026.0 |
| January 1, 1921 | 4,786.1 | 9,120.2 |