31 Switch/81 Switch

How did 31 Switch in Plaistow and 81 Switch in Rollinsford get their names? It doesn't appear to be distance since Rollinsford is less than 81 miles and Plaistow is more than 31 miles from Boston. Were there any other numbered switches on the B&M?

Thanks!

B&M Dover Numbered Switches: 1960's-70's

#39 Power switch from main line to west side of the yard, freight house area
#41 Power switch from main line to #2 main and east side of the yard (Present CPF-241)
#56 Handthrow switch from #2 main to freight yard (east of Oak St. Bridge)(by CPF-242)
#60 Handthrow switch from main line to west side of yard (east of Oak St.)

All tracks and switches #39 and #60 on the west side of the yard are long gone.

I believe remote control switches on the B & M refer to the lever numbers on the control machines. B & M did not use the CP (Control Point) numbers, which are at nearest milepost locations (usually), which around here started as a New York Central practice and carried through to Penn Central, Conrail and beyond.

So I'm guessing they were just numbered consecutively in their order from Boston. Is this correct?

You'll have to get someone really familiar with traffic control systems to tell you how the levers are numbered. The original traffic control system from Dover to PT Tower 1 dated from about 1928. It was substantially upgraded and changed about 1947. The control machine was located in Dover until 1958 and was moved to 150 Causeway Street in Boston. With the end of passenger service to Portland in 1965, Rockingham to Dover was single tracked and put under traffic control, so either the existing machine had a few more levers installed or another one was built for this segment, which had interlockings at each end and nothing much else. The Rockingham-Dover-PT Tower 1 equipment was moved from 150 Causeway to North Billerica about 1970. In the early 1970s, Plaistow to Rockingham was single-tracked and the disconnected Concord-White River Jct. control machine was wired up to control this segment.