Cambridge The line begins in
North Cambridge west of the Sherman Street at-grade crossing. The branch line proceeds west, and then south, where it has at-grade crossings at New Street, Concord Avenue, and the entrance road to the Walter J. Sullivan Water Treatment Facility at the
Fresh Pond reservoir. From there, the line proceeds to several underpasses, namely one below a second road into the Fresh Pond reservation, one at Huron Avenue, and one at Mount Auburn Street, where it then crosses the town boundary of Watertown.
East Watertown plans, highlighting
sidings (top right) of the rail line at the
Watertown Arsenal, ca. 1919 The line crosses Cottage Street at grade and Grove Street below grade. Further at-grade crossings were at School Street and at Mount Auburn Street just outside
Watertown Square.
West Watertown to Waltham The western portion of the branch continued past the Town Hall area, then headed southwest toward Main and Pleasant Streets (near Bacon and Howard Streets) and across Bridge Street in the
Bemis Neighborhood of Watertown. Although much of the area has been built over, from there the line ran adjacent to Pleasant Street through what are now mainly parking lot areas, through the Quincy Cold Storage property (now Repton Place) on Pleasant Street, through the former Raytheon property in Waltham, and across River Street near Willow Street, before crossing the
Charles River near the Bleachery Dam. The trestle for that crossing, approximately 140 years old, was dismantled and removed in August 2016. The line then crossed Calvary Street, then Newton Street, and proceeded across Pine Street before heading northwest, where it re-crossed the Charles, parallel to Elm Street. It then reached the
Central Square area, and looped back into the
Fitchburg Railroad main line.
Greenway Phase I of the Watertown-Cambridge Greenway connects School Street to Arlington Street, in Watertown, with a branch to the Arsenal Mall. Phase II connects with Phase I at Arlington Street and continues just past the Walter J. Sullivan Water Treatment Facility where it connects with the existing Fresh Pond Trail. ==Transformation to multi-use path==