Note: There was at least one mainline use of the double slip switch in the United States. It is documented in a Morning Sun book about the Erie Railroad, but I don’t have the book.
At Leavittsburg, Ohio, where the Erie Railroad mainline crossed a B&O branch line, there were double slip turnouts installed. I believe the Erie main may have been double tracked at the location, but by the time my friend Rich Cox and I got there to photograph the trackwork, the turnouts had been gone for some years–though from the scars on the ground one could tell where they had been located, and we were able to see old tie plates, etc. laying around.
Further to Paul’s post, another CTA location which has a number of double-slips, and which would take a ton of space to accomplish its functions if it didn’t have them, is Howard Street on the CTA (used by the Purple, Red and Yellow lines, as well as non-revenue trains going to/from Skokie Shops). There are two DSSs to the south of the station and six to the north. In addition, there are two more DSSs in the yard to the north of the station. Hope this helps, Art
Another main line use was just east of Ash St interlocking. A connecting track came off of the Chicago River & Indiana (NYC controlled a k a the CJ) and crossed both the double track mains of Santa Fe and IC (Freeport district IIRC), it went in the west end of the Chicago Produce Terminal yard. The four double slips were manually operated by a switchtender, not Ash St Tower.
There was a pair of double slip switches on the North East Corridor just outside the north portal of the B&P Tunnels in Baltimore. Everything going through the tunnel, freight and passenger, had to use one or both of the double slips. The switches were controlled by B&P Tower. There was such a reverse curve going through the switches that the ends of the Metroliners were fitted with ropes for Trainmen to block off passengers from passing between cars while going through the switches.
Here is a track diagram of the area with the notation that the ATSF switchtenders operate the double slip switches. There are ten switches inside the dotted box. Were only four of those double switches?
