Photo from the DeGolyer Library, Southern Methodist University. Courtesy of Myron Malone.
Isaac Conroe built a sawmill in 1881 a couple of miles from the International - Great Northern (I-GN) Railroad in Montgomery County. He built a tram to move freight between his sawmill and the railroad, but it wasn't long before he decided to relocate his sawmill to be near the I-GN tracks. When the Post Office opened a mail station at the new mill in 1884, the future town of Conroe began. A year later, the Gulf, Colorado & Santa Fe (GC&SF) Railway crossed the I-GN at Conroe. They were building a major spur into the east Texas timber region from a junction at their main line at Somerville.
For 45 years, the crossing in Conroe was officially uncontrolled; by law, all trains had to stop before proceeding across the diamond. The Railroad Commission of Texas (RCT) 1931 Annual Report lists Interlocker 170 as "Under Construction" as of 31 December 1930. It was the last entry in the interlocker list, and since this was the last annual report to include a complete list, Tower 170 has the distinction of being the final interlocker to be listed in an RCT annual report. The following year, RCT stopped listing interlockers and dates of authorization. The Tower 170 interlocker was most likely placed in service in 1931. It was most certainly not a manned structure; the high labor costs for manning a railroad tower limited their use to only the busiest crossings. Most likely it was either an electric interlocker (manually operated) or an automatic interlocker. Automatic interlockers had been allowed since the authorization order for Towers 141 and 142 in May, 1930, and they were well suited for crossings like Conroe that involved two major railroads that could both see steady traffic. Cabin interlockers were often used at crossings where the vast majority of the traffic was on one rail line, but it's unlikely that the traffic at Conroe was sufficiently disproportionate. Long before 1931, a union passenger depot had been built adjacent to the crossing. With this proximity, it is likely that if it was an electric interlocker, the controls were housed in the depot.
Above: The 1923 Sanborn
Fire Insurance map shows that the Union Depot was located in the northwest
quadrant of the crossing. There was one connecting track in the southwest
quadrant as well as a GC&SF
turntable and engine house.
Below: R.
J. McKay's 1981 photo shows the Union Depot.
Satellite and Street Views, Tower 170 Crossing
Above: The Tower 170
crossing is easy to spot in the middle of Conroe. The former I-GN route, now
Union Pacific, runs north/south
while the former GC&SF route, now Burlington
Northern Santa Fe (BNSF), runs east/west. Both lines continue to see regular
traffic.
Google Earth shows a line in the southwest quadrant that traces the
path of the former connecting track. Compare this image with the
Sanborn map
showing the location of the turntable and engine house.
Below: This Google Street View image looking east along the BNSF
tracks shows the interlocker equipment
cabinet in the southwest quadrant of
the crossing. 
