The original Montrose Tower is seen on the left, looking north across Montrose Interlocking in the mid-1910s. The tower controlled two access points to Lower Wilson Yard -- switches to a two-track ramp diverge off to the right, while directly in front of the tower is a one-track incline down to the lower yard, later removed -- as well as into the south end of the Wilson upper yard. Wilson Shop is in the background. For a larger view, click here. (Photo by Frank M. Hollenbeck, courtesy of the Krambles-Peterson Archive)

Montrose Tower
Montrose Avenue and Kenmore Avenue, Uptown

Service Notes:


North Side Main Line

Quick Facts:

Established: 1900
Original Line: Northwestern Elevated Railroad
Rebuilt: 2021
Status: In Use



There have been two different interlockings at Montrose on the North Side Main Line during two different periods.

Layout of Montrose Interlocking in 1913. For a larger view, click here. (Reprinted from Instructions to Trainmen in Connection with Through Routing, issued by CER to employees in 1913, Graham Garfield Collection)

The original Montrose tower and interlocking were located at Montrose Avenue, between Wilson and Buena stations, at the south end of Wilson Yard. The interlocking plant at Montrose controlled access to both the south end of the elevated (or "upper") Wilson Yard, as well as movement of trains to and from Lower Wilson Yard. The switches in the interlocking plant consisted of turnouts from track 2 (southbound express track, post-1913) and track 4 (northbound local track, post-1913) to a two-track curved alignment that skirted the south side of the yard, providing a switch into the upper yard and a two-track line on an incline down to the lower yard. In addition, north of these main line switches there was a turnout from track 4 directly into the upper yard, and a switch that connected a second, one-track incline from the lower yard alongside the west edge of the mainline, connecting into track 1 southbound. The plant was completed with a set of crossovers on the main line -- a left-hand crossover between track 1 and 2 and a right-hand crossover between track 3 and track 4 -- at the south end of the interlocking plant to allow trains to switch tracks approaching or coming off these yard leads.

A two-story tower building was located on the west side of the main line right-of-way, on the south side of Montrose Avenue, cantilevered off the elevated structure. The building itself was fairly utilitarian in style, a sheet metal-clad two-story building with a hipped roof.

The interlocking plant it controlled was mechanical, with the switches and wayside semaphore signals controlled by large levers in the tower that were connected through a "locking bed" to a series of rods along track level that manipulated the switch points and signal arms. The locking bed consisted of steel bars forming a grid constructed so that, if the function controlled by a given lever conflicts with that controlled by another lever, mechanical interference is set up in the cross locking between the two bars, in turn preventing the conflicting lever movement from being made.

A second, similar tower at Wilson, a new blocks north, controlled access to the north end of Wilson Yard, as well as in and out of the Wilson terminal station.

Sometime between 1913 and 1949, a series of changes was made to Montrose Interlocking. The ramp between the lower yard and the main line connecting at Montrose was removed, in favor of a new incline connection between a separate freight interchange track west of the main line and the lower yard. In addition, the switch directly from track 4 into the upper yard had been removed, and the left-hand crossover between tracks 1 and 2 at the south end of the interlocking had become a right-hand crossover (making for a pair a right-hand crossovers here, between tracks 1 and 2, and between tracks 3 and 4).

Effective August 1, 1949, the new CTA enacted a restructuring of service on its north-south lines, and as part of this passenger trains no longer used the Lower Wilson station. As such, train movements on and off of the incline to the lower yard were reduced to equipment moves, though in the short term the lower yard continued to be regularly used, so Montrose remained interlocked and tower-controlled. It is likely that, around this time, staffing of the tower was reduced, as was the case in many locations around the "L" system as the CTA looked to streamline operations and reduce labor costs, and was the case at Montrose's sister tower at Wilson at the north end of the yard. However, when this may have occurred and to what degree is unclear.

As usage of and frequency of movements in and out of the lower yard decreased, the need to have two connections to it, let alone a tower-controlled, interlocked one, was severely diminished. Sometime between December 1951 and November 1952, the two switches from the main line to the incline to the lower yard were removed, and the ramp was removed from service. By the same time, the two right-hand crossovers (between tracks 1 and 2, and between tracks 3 and 4) were changed to hand-throw switches. At this point, Montrose Tower appears to have been out of service. It was demolished sometime thereafter.

The two manually-operated right-hand switches remained the status quo at Montrose for the next 40-plus years.

Circa 1996-97, a decision was made to revamp the interlockings at Wilson and at Armitage, both to renew the track and signal infrastructure as well as to rationalize the layout of the switches to make these interlockings more useful. The layout of the switches at Wilson (as well as at Armitage) were reconfigured to be a giant X, allowing for movement between any of the four tracks. The layout at Wilson consisted of a universal crossover (a set of left- and right-hand crossovers) between tracks 2 and 3 south of Wilson station (actually located between Sunnyside and Montrose avenues, interlocked and controlled from a new Wilson Tower. The layout was completed with four hand-throw switches -- two north of the new Wilson interlocking and two switches south of Montrose Avenue, where the two switches remaining from the old Montrose Interlocking remained. Circa 1997, these two old hand-throw right-hand crossovers at Montrose were removed, replaced with a right-hand crossover between tracks 2 and 1, and a left-hand crossover between tracks 4 and 3; these two switches at Montrose were hand-throw, not controlled by the new Wilson Tower.

These Montrose crossovers remained in service until 4am, Monday, June 29, 2020, when the right-hand crossover between tracks 2 and 1, and the left-hand crossover between tracks 4 and 3 were officially removed from service. In reality, however, they had been physically removed some weeks before as part of the construction of the new Montrose Interlocking (described below), with the right-hand crossover between tracks 2 and 1 removed during the week of June 14 and the left-hand crossover between tracks 4 and 3 removed the week of June 21. Both were replaced with diamond crossovers in the same general locations.


A New Montrose Interlocking

As part of the CTA's Red-Purple Modernization Program (RPM), a new interlocking was planned to be installed at Montrose. RPM's Lawrence to Bryn Mawr Modernization (LBMM) project includes replacement of the four-track embankment between Leland Avenue (south of Lawrence station) and Ardmore Avenue (between Bryn Mawr and Thorndale stations) with a new elevated structure, which would be built in halves (referred to as Stage A and Stage B by the project) so that two tracks can remain in service through the construction zone at all times. To achieve this, new interlockings are needed at the north and south ends of this zone to merge and sort trains transitioning between the 4-track and 2-track zones.

The interlocking at the south end of the LBMM area is at Montrose Avenue. The new interlocking includes three diamond crossovers -- one between tracks 2 and 3 at the north end of the interlocking plant north of Montrose Avenue, and a pair between tracks 1 and 2 and between tracks 3 and 4 at the south end south of Montrose Avenue -- and a new tower.

The work also included the decommissioning of the existing Wilson Interlocking and removal of those two interlocked switches as well as the two existing hand-throw switches near Montrose. The decommissioning and removal of those switches immediately preceded the installation of the new interlocking's switches, as the new ones are generally the same area as the old specialwork. The interlocking at Wilson was removed from service effective 10pm, Friday, February 7, 2020; the official out-of-service dates for the old Montrose crossovers are detailed above.

Construction to install the new interlockings at Montrose and Thorndale each had its own set of challenges. At Montrose, the installation of the special trackwork was more challenging than installing the signal and other system infrastructure due to it being on the open-deck steel elevated structure. Because of how CTA attaches the tracks to the steel stringers of the older "L" structure, using hook bolts (also called J-bolts), and because the diamond crossovers are custom-made and are massive pieces of steelwork to be hoisted and set in place, there is little room for error in assuring the pieces fit just right and the locations for the bolts align properly. This made placement of the specialwork exacting and challenging work. On the other hand, because the deck underneath was open, stringing the signal, communications and power cabling was somewhat easier to do here than at Thorndale Interlocking, whose construction had the opposite challenges.

During June 2020, the old crossovers at Wilson and at Montrose were removed and the three new diamond crossovers were installed during a three-week series of consecutive reroutes on the north main line. Each phase of these reroutes shifted service between tracks to provide the necessary access for the RPM contractors to install the new trackwork. The reroutes began at 10pm, Friday, June 5, and last reroute in the series ended at 1am, Monday, June 29.

During this period, the 4-track main line was reduced to two tracks, resulting in Purple Line Express trains running on the same tracks as the Red Line between Granville (or in some cases, Howard) and Belmont on weekdays; however, only the normal express stops were made. Running the two services together caused relatively few delays to service, as service levels on both routes had already been reduced and interval between trains widened due to depressed ridership levels caused by the COVID-19 pandemic and resulting increase in people working from home or otherwise altering their travel patterns. Other more significant service impacts during some phases included reroutes resulting in southbound trains bypassing Jarvis through Lawrence, with a southbound bus shuttle from Howard to Wilson, from 10pm, June 5 to 10pm, June 6, and again from 11am, June 20 to 4am, June 22; and southbound trains bypassing Argyle and Lawrence (with customers required to "backride" to/from these stations southbound) from 10pm, June 6 to 11pm, June 12, and again from 4am, June 22 to 4pm, June 27. During other reroutes there were some minor impacts such as boarding changes at Sheridan or Wilson, but otherwise all stations were served.

The "extended reroute" approach to the interlocking work reduced the number of days in which both passengers and the local community were impacted by construction by exchanging shorter-duration weekend reroutes for a longer reroutes that included weekdays. Similar to the CTA’s approach for the Red Line South Reconstruction Project in 2013 that rebuilt the Dan Ryan branch’s track system from the sub-grade up, it “ripped off the band-aid” and reduced overall impacts while improving contractor efficiency by reducing time spent mobilizing and remobilizing equipment and staffing over successive weekends.

The extended reroutes installed the new trackwork and some other associated infrastructure for the two new interlockings, but they were not functioning, tower-controlled interlockings at the end of each extended reroute. There still remained much work on signal, communications and power systems at each location, and commissioning activities to complete. This was true not only at the new interlockings, but along the whole route from Montrose to around Loyola, all of which received new bi-directional cab signaling to support the 2-track operation and provide new, more stable signal infrastructure for during construction. The new Montrose relay house was delivered to the site on Friday, August 28, and was lifted and set on its platform at track level on Saturday, August 29.

Over two weekends in October, closures of two tracks at a time with reroutes allowed for the installation of new tapered ties super-elevation in the curves at Montrose to permit higher speed operation through the curve in the middle of the interlocking. Tracks 1 and 2 were done over the weekend of October 2-5, and tracks 3 and 4 were done over the weekend of October 9-12. In both cases, the outside express track remained closed two extra days, through Wednesday morning of the following week, to permit work to be finished, requiring Purple Line Express trains in one direction to run on the Red Line track.

Equipment installation, testing and commissioning work on that new signal system continued through fall, winter and spring into May 2021, with parts of the interlocking coming online as certain activities were completed. On Monday, March 15 at 12 noon, all of the wayside interlocking home signals (both normal and reverse movement signals) were placed in service at Montrose Interlocking. However, the related switches remained clamped in the normal position until the interlocking was fully tested and placed in service; the turnouts functioned as hand-throw switches, and could be operated by Power and Way Maintenance Signal Maintenance personnel as needed.

On Friday, May 14, 2021 at 10am, Montrose Interlocking was placed in service, with all switches and signals available for use from local tower panel.

RPM LBMM Stage A construction, when 2-track operation began between Montrose and Thorndale interlockings, began at 12:01am, Sunday, May 16, 2021. Tracks 3 and 4 closed, and all trains used track 1 (southbound) and track 2 (northbound) between Montrose and Thorndale. Tracks 3 and 4 remained available between Montrose Interlocking and the north end of the Wilson station platforms as storage tracks -- there is space to store 16 cars on track 3 and 24 cars on track 4 north of Montrose Interlocking -- though routes into and out of the storage tracks could only be established from the tower, not the wayside route selectors.

Installing, testing and commissioning work for additional functionality at Montrose Interlocking continued through May and into June, including the ability to put the interlocking on automatic during off-peak periods and have routes automatically established for Red Line trains, and automatic vehicle identification (AVI) to detect and differentiate approaching southbound Red Line trains from Purple Line trains and automatically establish southbound routes from Track 1 onto Track 2 for Red Line trains and onto Track 1 for Purple Line trains.