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The Southern Pacific built east from Los Angeles reaching Yuma in September 1877, Casa Grande in May 1879, Tucson in March 1880, and El Paso in May 1881. The Buffalo Bayou & Colorado Railroad began building west from Houston before the Civil War. After the war it was reorganized as the Galveston, Harrisburg, & San Antonio and began building west again in 1870. It reached San Antonio in February 1877, then in May 1881 built west to meet the SP. The SP continued building east out of El Paso under the charter of the GH&SA in a race to cut off Jay Gould's Texas & Pacific. The SP under Huntington reached Sierra Blanca on November 25, 1881 while the T&P was just ten miles to the east. The next day Huntington and Gould met in New York and signed an agreement whereby the Texas and Pacific agreed not to build west of El Paso and the SP granted the Texas and Pacific trackage rights between Sierra Blanca and El Paso. The last spike on the Sunset Route in Texas was driven on January 12, 1883 about three and a half miles southwest of the present Pecos River bridge on a portion of line abandoned during 1892.
The GH&SA came under SP control in 1885 and was absorbed into the Texas & New Orleans in 1927. The T&NO was absorbed into the SP in 1961. In 1909, there were signals Avondale to Morgan Ciity 68 miles, Lafayette to Lake Charles 72 miles, Lake Charles to Sabine River 31 miles, Echo to Englewood 103 miles, Houston to Seguin 173 miles. Signals across the western end of Sunset Route came in little chunks. In 1923, the GH&SA ordered 45 US&S lower quadrant semaphore signals for station protection at the following stations located between San Antonio and El Paso: Uvalde, Noonan, Sabinal, Alpine, Toronto, Paisano, and Marfa. The stations received 6 signals each stretched across about five miles. Spofford and Macdona also received 6 signals each in 1924. The railroad added signals from Ysleta to Grayton in 1924, Osman to Sanderson, Cline to Hacienda, Grayton to Sierra Blanca in 1925, Cline to Del Rio, Osman to Langtry, and Longfellow to Marfa in 1926, and Marfa to Hot Wells in 1927.
A separate pole line was used for signal operations. The poles were set 40 to the mile. At the time a pole cost $6.25 and it cost $1.50 to set a pole. A special grounding wire is set above the crossbar carrying all of the block signal wires for lightening protection. The lightening wire runs to ground every fourth pole. When completed in 1927 there were 1,190 miles of automatic block signals from New Orleans to El Paso. There were train order stations at El Paso, Sierra Blanca, Valentine, Marfa, Alpine, Marathon, Sanderson, Dryden, Langtry, Del Rio, Spofford, Uvalde, Sabinal, Hondo, Lacoste, San Antonio, Seguin, Luling, Harwood, Flatonia, Glidden, Eagle Lake, Tower 17 in Rosenberg, Eureka, Houston Tower 87 in Englewood Yard, Dayton, Devers, Beaumont, Orange, Echo, Lake Charles, Jennings, Midland, Crowley, Rayne, Lafayette, Baldwin, Morgan City, Schriever, Raceland Junction, and Avondale Yard in New Orleans.
CTC was installed in short segments near major terminals in the 40s and 50s and were generally controlled from nearby train order stations or interlocking towers. The first CTC segment outside a major terminal was from Paisano to Alpine in 1930. US&S electric interlockers were also installed in early 1930 at Sanderson and Sierra Blanca. The next segment was Harrisburg to Rosenburg 34 miles in 1953. The semaphore signals were replaced with searchliight signals. The CTC machine was in San Antonio. At the time, the line had four Santa Fe passenger, four SP passenger, four freight trains, and two locals per day. The next segment of CTC installation was from El Paso to Sierra Blanca. The work was completed in 1960 after installing 19 power switches and 92 signals. The T&P helped pay for part of that project. In 1973 the SP began installing CTC at Flatonia working its way west and completed the project in 1974. SP added CTC between Rosenberg and Eagle Lake in 1994. UP installed CTC Eagle Lake to Flatonia in 2000. For reference, I've added a timetable for the Valentine Subdivision.