Tower A to East Somerville Junction (FX) and Reading Junction

From the interlocking at Tower A (MP 0.3), on the north bank of the river, where there are crossovers and the lines split three ways: the Fitchburg Route Main Line (Fitchburg Line) heading west-northwest; the New Hampshire Route Main Line (Lowell Line), continuing northwest; and the combined Eastern/Western Route Main Lines (Newburyport/Rockport Line and Haverhill Line) heading north-northwest, the latter is three tracks wide (Tracks 2, 3 and 4), CTC, with speed limit 25 mph for passenger trains and 20 mph for freight trains, past the crossovers at FX (MP 1.4), aka East Somerville Junction, where there is a 20 mph speed restriction over the flat crossing with the CSX freight line between Beacon Park Yard and East Boston, within the interlocking, and the number of tracks reduces to two (Tracks 1 and 2), turning north to the crossovers and junction at Reading Junction (MP 1.8), where the two tracks of the Eastern Main Line, heading northeast, separate from the single track of the Western Main Line, heading north.