The Lake Street Elevated Railroad's ability to provide express service was initially hampered in the same way as the South Side Elevated was: it was built as a two-track line its entire length. This meant that expresses would have no easy way to overtake slower moving local trains. Like the South Side later did, the Lake Street constructed a center track in 1894, but unlike the South Side it was not meant to serve express trains but rather to solve another problem ailing the Lake Street: car storage. The track, which extended west from Rockwell Street and eventually went all the way to 40th Avenue (Pulaski), was used to lay up cars not in service for the next seven decades, even after the Hamlin Yard was built in 1895.
The first express service run by the Lake Street Elevated was not actually to serve the stations along the main line route, but rather an excursion service to the Harlem Race Track near Roosevelt Road and Hannah Avenue in the Village of Harlem (now Forest Park). The race track specials operated to and from the Loop via the Lake Street Elevated, then switched to street running in Cicero Township following Lombard, Randolph, Cuyler, Harrison, and the Suburban Railroad's streetcar trackage (72nd Avenue, 13th Street, Hannah Avenue). Service started May 30, 1899 and was well patronized, despite a hefty 25 cent round-trip fare (these trains were not restricted by the 5 cent fare clause in the Lake Street's franchise). Eight five-car trains left the Loop between 1pm and 2pm and ran nonstop to the track. The 11-mile ride took just 25 minutes. To overtake slower-moving locals, meets were scheduled in which the locals moved into the center storage track west of Rockwell Street and waited for the specials to pass.
The fact that the race track (which was considered a place of low moral character) could receive express service and not the citizens of Oak Park would become a bone of contention. The race track specials did little the enhance the Lake Street's already tarnished image with Oak Park, not so much because it was carrying persons to and serving a place of ill-repute, but because it gave the appearance that fewer trains were serving stations west of Austin.
On August 8, 1902, the Oak Leaves, Oak Park's local newspaper, carried an ad that no one thought they'd ever see: an announcement heralding the beginning of Lake Street express service. Express service began August 11, 1902 between the Loop and Oak Park. Trains left the Wisconsin/South Boulevard terminal every ten minutes in the morning from 6:15am to 8:35pm and from the Loop every six minutes in the evening from 4:35pm to 6:20pm. No morning service was initially provided from the Randolph Street branch, although two evening trains served the branch. Expresses used the center track to make no stops between 48th Avenue and Oakley Avenue and by-passed three other stations between Oakley and Canal. The trains were so successful that Saturday express service was soon added. On September 29th, three morning and two more evening trips were added to serve the Randolph branch as well.
But if the expresses were using the center track for express service, what happened to the cars in storage? It turned out that Lake Street president Clarence Knight had come up with a cheap solution for the elevated. The street trackage on Randolph of the Suburban Railroad east of Lombard was, for all intents and purposes, no longer in service. So, Knight made an agreement with the Suburban in which the Lake Street stored the displaced cars on the street during midday hours. Needless to say, the residents along Randolph Street were none too thrilled to discover that their street had been turned into a car yard. In September, the Village of Oak Park passed a resolution directing the Lake Street to remove the cars, but Knight countered that if he were forced to remove them, the express service would have to be terminated. After a series of fruitless negotiations, Oak Park ordered Knight to remove the cars.
True to his word, express service to Oak Park was suspended on November 10, 1902. Knight had refused to find an alternate storage site and moved the cars back onto the center track. Riders, who had become accustomed to fast service to the Loop, deserted the Lake Street in droves for the parallel Chicago & North Western. So severe was the drop in ridership and revenue as a result that Knight lost no time securing permission for a temporary storage site for the cars until the center track could be extended at 40th Avenue just enough to hold the 14 cars that has started the whole mess. On November 12, 1902, express service to Oak Park was reinstated. Express service on the Randolph Street branch lasted only until December 21, 1903, when all service was discontinued on that line.
On October 6, 1906, the successor Chicago & Oak Park Elevated instituted a new express schedule which reduced running time between Wisconsin Avenue and the Loop to just 28 minutes. The new express trains operated on a 4-5 minute headway in the morning and skipped all stations between Central and Oakley and between Ashland and Halsted. A supplemental express service, following the old stopping pattern, was retained. Evening serving was increased by scheduling some expresses out of the Market Street terminal. On the first day, 54,000 people ride the new service.
Lake Street express service remained more-or-less the same over the years, but was tweaked a little bit. When the CTA® look over in 1947, the Lake Street Division was running the following local/express schedule:
Outside of rush hour, Forest Park-to-Loop locals were the norm. There were also some weekday midday Shoppers Specials that ran every half hour express from Hamlin to the Loop, possibly added to the schedule in December 1923.
In spite of a line that would seem to have a good mix of locals and expresses, the CTA® described the Lake Street Line as a "conglomeration moving at a slow speed." The express trains could only operate in one direction and even then, the center express track only ran part of the length of the line. All of the line's cars were old wooden motors and trailers, which moved slowly and were in an advanced state of aging. Stations were spaced closely (every two blocks, in some parts) making it scarsely faster then parallel streetcars and buses and express operations were limited, since the center track had to be used for storage off-peak. After a period of study and deliberation, the CTA® abandoned all local/express service on the Lake Street Line and instituted a new skip-stop scheme instead.
The Lake Street was the first line to receive the CTA®'s new A/B skip-stop scheme on April 5, 1948 because it was considered the most dire case on the rapid transit system. Stations were designated "A" stops, "B" stops, or "AB" stops, while trains were designated "A" trains, "B" trains, and "All-Stop" trains, with each stopping only at their respective stations. The "A" and "B" stops were alternated and mixed in with the "AB" stops (although the entire western end of the line beyond Pulaski were "AB" stations). Ten stations were closed, all trains were routed onto the Loop, and the center express track was taken out of revenue service, used only for car storage. Running time was cut from 35 minutes (for locals) to 24 minutes. The A/B system was spread to other lines after the Lake Street experiment was deemed a success.
When what now is the Green Line (Lake-Ashland/63-East 63rd) was shut down for extensive renovation in 1994, the express track was removed and not restored.