The Northwestern Elevated was built to a rather unique design for Chicago. While the rest of the city's elevateds had been built as two-track lines, the Northwestern was a four-track operation (except for south of Chicago Avenue), allowing for express and local operation. Local stations were spaced approximately every quarter mile, with dual side platforms serving the two outside tracks, where local trains were to be operated. Express/local stations were placed at approximately one mile intervals -- at Sheridan, Belmont, Fullerton, Halsted, Sedgwick, Chicago, and Kinzie -- and typically had two island platforms that each served both the outside local track and inner express track. (Chicago, and Kinzie had only side platforms, as the line was only two tracks there). This dual-island platform layout at express/local stations made for an easy cross-platform transfer from locals to expresses.

For the first month or so, only local service was operated, but express service was added in July 1900. Express service operated during rush hours between Wilson and the Loop. Expresses originally stopped at Sheridan, Belmont, Fullerton, Halsted, Sedgwick, and Kinzie, but express stopping at Halsted and Sedgwick was short-lived, suspended in September 1900. Express service went through many revisions as the years went on. Starting in 1902, some northbound afternoon expresses made local stops north of Fullerton to give passengers heading to these stations a faster trip. At some point, Chicago was added as an express stop.

In 1907, a second, separate terminal was added at Wilson, small stucco station house designed by architect Arthur U. Gerber with two platforms on the Evanston Avenue (Broadway) side of the yard was built at ground level known as Lower Wilson. The layout included a loop track, so turns could be turned easily for the return trip. "Lower Wilson" opened on March 5, 1907 and, according to the Chicago Daily News, handled all express trains. Locals continued to be handled at the old "Upper Wilson" station.

A flurry of extensions opened around the same time. The Ravenswood branch, leaving the original main line at Clark and Roscoe and taking a meandering path northwest to Lawrence and Kimball in Albany Park, entered service on May 18, 1907 as far as Western Avenue and reached the final terminal at Kimball on December 14, 1907. On May 16, 1908, the Northwestern Elevated extended trains north of Wilson beyond the city limits at Howard to Central Street in suburban Evanston. The Evanston extension utilized the electrified track of the exiting Chicago Milwaukee & St. Paul steam railroad, reaching the ground-level extension by means of a short extension of the elevated structure across Evanston Avenue [Broadway], then down a two-track ramp to the St. Paul's tracks.

The Northwestern took the opportunity of the opening of the extensions to overhaul their operating scheme. Upper Wilson and the original elevated 1900 station now handled Evanston trains, both locals and expresses. Lower Wilson continued to handle all Wilson-Loop express runs. The schedules and stopping patterns used by the Northwestern following the opening of the Evanston Extension appeared in the May 23, 1908, issue of the Street Railway Journal:

A complete rearrangement of the schedule of the entire line has been worked out to accommodate the extra trains which will be run over the new extension. Through trains will leave the terminal at Central Street, Evanston, every 10 minutes from 6 a.m. until midnight, making all stops to Wilson Avenue. During the rush hours they will run express between Wilson Avenue and the Loop, but between 9 a.m. and 3 p.m. and after 7 p.m. they will run local from Wilson Avenue to Belmont Avenue and then express to the Loop. Between every two Evanston trains one Wilson Avenue Express will be started during the non-rush hours, giving a five- minute service south of Wilson Avenue, and during the rush hours two extra trains will be run, giving a 3 1/3-minute service. The Wilson Avenue expresses will also run local north of Belmont Avenue during the non-rush hours. In addition to this express service Wilson Avenue local trains will be run at intervals from 4 to 5 minutes. Trains for the Ravenswood branch which now run express south of Belmont Avenue at all hours will run at 5-minute intervals as local trains during the non-rush hours and as express south of Belmont Avenue during the rush hours. This will give a 2 1/2-minute local service and 5-minute express service during the non- rush hours south of Belmont Avenue and a 4-minute local and 2-minute express service during the rush hours.

The service on the Evanston extension will be started with two-car trains, adding and cutting off additional cars southbound and northbound respectively at Wilson Avenue. The running time between Central Street, Evanston, and Wilson Avenue will be 20 minutes, and from Wilson Avenue to the Loop 20 minutes, with 13 minutes on the Loop. The total time from Evanston to the Loop stations will average therefore about 45 minutes, as against 33 minutes by Chicago & North Western suburban trains, which land passengers, however, at Kinzie Street across the river.

The rush hour express services provided very popular and in short order the Northwestern increased their consists to five cars to satisfy the demand. Stopping patterns south of Wilson Avenue were also modified on occasion to speed service and reduce crowding.

By 1907 the Loop had already reached capacity, requiring the original three lines to reopen their stub terminals at Congress, Market and Wells, which were closed when the Loop opened. Though the Northwestern Elevated, unlike the other three lines, always ran into the Loop, they too saw the wisdom in a terminal for rush hour overflow just outside the Loop. The North Water Terminal, located on a short branch off the North Side Main Line just north of the Chicago River over North Water Street (later renamed Carroll Avenue, really little more than a glorified right-of-way in which the Chicago & North Western Railway), opened in November 1908. Upon its opening, operating patterns were again revised. The North Water station was only used during rush hours. During the morning rush, express trains were dispatched from Howard Street at a 10-minute interval (making all stops to Argyle, then express stops to downtown), with four trains service North Water and the remainder going around the Loop. Express trains from Central Street, Evanston operated nonstop from Howard to Wilson, then made express stops to downtown. Various Wilson and Ravenswood expresses were also operated the the stub terminal. During the afternoon rush, expresses were operated to Ravenswood, Wilson, and Howard.

In March 1909, a rush hour express service was added between Kimball and the Loop.

On November 3, 1913 the North and South side lines were through-routed under the auspices of the new Chicago Elevated Railways (CER) holding company. Initially, Evanston-Jackson Park Expresses and Wilson-Englewood Expresses were operated daily. There was also initially a Wilson-South Park [King Drive] Local, although it is believed that this was a short-lived operation. Ravenswood trains were through-routed to Kenwood, although because traffic was heavier on the former than the latter there were also Ravenswood-Loop runs. Apparently, there were also some Ravenswood-61st Street trips in the mornings. At first, through-routed and express trains only ran during day and evening hours, with trains running local and only as far as the Loop at other times. Gradually, however, through-routed expresses and locals were added at night to meet heavy demand. The exact stopping patterns and service hours changes many times through the years, although the exact nature of all the changes is not precisely known.

The elevation of the at-grade tracks between Lawrence and Howard, required by the Northwestern Elevated's 1907 ordinance, began on April 22, 1914 and resulted in numerous operating changes to accommodate both demand and construction staging. The tracks were elevated using wooden trestles that had retaining walls built around them and filled with rubble and earth to make a solid-fill embankment. Ultimately, the two-track line was expanded to four tracks so that the North Side Main Line had a four-track express-local operation clear from Chicago Avenue to the city limits at Howard.

In January 1916, trains were moved into a temporary wooden trestle and the turning back of certain northbound rush hour trains at Howard was discontinued. Instead, the first three cars of these trains continued to Linden (where the Northwestern had been extended to from Central in 1912) and the rest of the cars were attached to a southbound train at Howard. By mid-1921, the elevated was nearly complete and three tracks were in use. The westernmost track was being used by southbound expresses, while the other two were used for local trains and northbound expresses. During rush hours, southbound Evanston Expresses made local stops from Linden to Loyola, then ran nonstop to Argyle, then made express stops to the Loop. Trains originating at Howard ran local to Argyle, then express to the Loop. At the time, Argyle temporarily had a three-track, two-platform arrangement, allowing easy transfers.

In 1922, the elevation was completed. There were now four tracks from Chicago to Howard, but unlike the original section south of Wilson the new alignment north of Wilson had a different arrangement. The express tracks were on the outside and the local tracks were the two inside ones, the opposite as south of Wilson. All of the new stations from Argyle to Jarvis had only a single island platform in the center between the two local tracks (Lawrence, added in 1923 between Wilson and Argyle had the same arrangement). Only the new Howard station had two island platforms to allow express/local stopping and cross-platform transfers, although crossovers at Loyola and Granville allowed some operational flexibility. Evanston Expresses continued to make all stops from Linden to Loyola, but then made only express stops to the Loop, ceasing to call at Argyle. Howard trains ran local to Wilson, then express to the Loop.

On February 23, 1931, the Chicago Rapid Transit (CRT), the now-merged company, made a few changes to crosstown service. The Wilson-Englewood and Ravenswood-Kenwood through-routes were swopped. To better adjust to the traffic patterns, these through-routes were only in effect in rush hour; at all other times, the trains terminated in the Loop. On the Jackson Park-Evanston and Jackson Park-Howard trains, the hours of express service was reduced.

With the opening of the State Street Subway on October 17, 1943, the Loop's severe congestion could finally be relieved. Jackson Park-Evanston/Howard and Englewood/Normal Park-Ravenswood trains were rerouted to the new subway. Englewood and Ravenswood express trains were through-routed at all times from then on, as were the Kenwood-Wilson trains. To serve the busier North Side stations, the Wilson-Loop locals were also kept.

These types of mixed express and local services on the same routes ceased on August 1, 1949, when the CTA^® instituted its massive North-South service revision. The myriad of complex express/local operations to multiple destinations were discontinued and the CTA^® streamlined the services into much simpler routes. Service was organized into the following routes: Howard-Englewood, Howard-Jackson Park, Ravenswood (Kimball-Loop), and Evanston (Linden-Howard during non-rush hours, Linden-Loop during rush); as well as several shuttles on the South Side. The Howard-Englewood-Jackson Park Line (also known as the North-South Route) was routed through the State Street Subway at all times, while the Ravenswood and Evanston Express services were permanently placed on the Loop elevated. Express service was still operated, but instead it was in the form of the CTA's^® A/B skip stop service. The Evanston Express, operating during rush hours only, became the last remnant of this old-style type of express service (see seperate page for more on this service).

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Certain information drawn from The "L": The Development of Chicago's Rapid Transit System, 1888-1932 (CERA Bulletin 131) by Bruce G. Moffat.