MBTA Subway Chaining
MBTA subway routes use chains to note distance along the right-of-way. These function similar to mileposts on mainline tracks, except use the Engineer's chain (100 ft / 30.5 m) instead of miles/kilometers.
Chaining markers are usually placed along the right-of-way. Chain markers are formatted in the following way: 1 letter for the chain line, 1 letter for the track direction, 2-3 digits for the whole chain, and a "+" 2 numbers for the amount of feet beyond the whole chain. (BE 060+00 for 60 chains beyond chaining zero on the eastbound Blue Line)
Chaining Lines
[edit | edit source]| Chain Prefix | Directions | Line | Chaining Zero | Towards |
|---|---|---|---|---|
| B | E/W | Blue Line | Bowdoin Loop (055+00) | Wonderland |
| A | E/W | Green Line Core | Main Line Switch East of Kenmore | Medford/Tufts |
| B | E/W | Commonwealth Ave | Main Line Switch East of Kenmore | Boston College |
| C | E/W | Beacon St | Main Line Switch East of Kenmore | Cleveland Circle |
| D | E/W | Highland Branch | Switch at Beacon Junction | Riverside |
| E | E/W | Huntington Ave | Switch at Copley Junction | Heath St Loop |
| R | N/S | Red Line Core | North of Alewife Yard | JFK/UMass |
| A | N/S | Ashmont Branch | North of Alewife Yard | Ashmont |
| B | N/S | Braintree Branch | North of Alewife Yard | Braintree |
| O | N/S | Orange Line | South of Forest Hills Yard | Oak Grove |
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