It’s both an anomaly and an outlier, a transit afterthought among the 224.1 miles of track that make up the Chicago Transit Authority’s rail system. In a city synonymous with the Loop, and the elevated trains that sail through its rows of downtown skyscrapers, the CTA’s Yellow Line, still affectionately referred to by its original name, the Skokie Swift, runs a 5.1-mile, three-stop route through the suburbs and far northwest side of the city, skimming the surface along a gravel-lined path.

Just look at the system map; the Yellow Line hangs at the edge of the rail network like an apostrophe or an afterthought. During a brief period nearly a decade ago, when I worked on the northwest suburbs but lived in Chicago’s Roscoe Village neighborhood, I regularly rode the Skokie Swift as part of a complicated, car-free commute, where a multiplicity of lines and vehicles (Brown Line, Red Line, Swift, and a bus) carried me to the office everyday. The Swift, which zipped along its brief route, was the oddest part of my journey, like a theme park tram that cut through the suburbs. It felt like I barely had the time to crack one of the many books I read to-and-from work that year.

But there’s a lot more to the story of Chicago’s Yellow Line than its small stature and seemingly miniscule service area. The Skokie Swift wasn’t built to be a rarity. It was born to be revolutionary. The result of unique circumstances, progressive vision, and a smart federal investment in urban transportation, the Swift was actually a laboratory on rails, a truly American mass transit innovation built as a response to suburbanization.

Its relative unfamiliarity to today’s riders becomes even more interesting when stacked up against the line’s incredible, frankly unbelievable success. The Skokie Swift was actually a vision of what could have been, and influenced many of the country’s largest mass transit systems.

“You can see the DNA of the Skokie Swift concept in a lot of systems planned in the ‘60s,” says Graham Garfield, CTA’s general manager of Customer Information and the agency’s unofficial historian. “Systems like MARTA, BART, and the DC metro, they’re all hybrid rapid-transit commuter rail systems that extend out much farther than typical rapid transit systems would. That’s the Skokie Swift model.”

The Skokie Swift experiment, which took shape in the early ‘60s, resulted from a number of coincidences. The most important was an empty rail line. Originally known as the Niles Center (the original name of Skokie), the track that connected Skokie to Chicago was once utilized by the old Chicago Rapid Transit Company, a CTA precursor, as well as the Chicago North Shore and Milwaukee Railroad. By 1963, service had ceased, which caused consternation in Skokie, then a booming northwest-side suburb which feared the result of being untethered from regular transit to Chicago. Later, when reflecting on the success of the Skokie Swift, a CTA leader would remark that it managed to make good on a line that had failed twice before.

At the same time, the federal government was putting money into improving mass transportation. In 1961, President Kennedy signed the Housing Act, which included $25 million to fund mass transit demonstration projects. In his signing remarks, the President stated that “it was the first time federal aid was being provided to improve inadequate public transportation.” At the time, there was no Department of Transportation (the agency wasn’t created until 1967), but Kennedy and his administration had already seen how housing and transportation were inexorably intertwined.

It took CTA employee George Krambles to bring everything together. A “transit renaissance man” according to Graham, Krambles, who spent decades as an engineer and planner for area transit agencies, has been called the father of urban light rail for his work on this project. He saw the line’s potential, and the availability for federal aid, and envisioned an opportunity: create a fast, efficient rail service geared towards getting suburbanites out of their cars. Don’t just extend the same old mass transit solution to the suburbs, but test out a new rail system, one specifically geared toward addressing suburbanization and sprawl and efficiently linking commuters with the city’s existing transit system.

Before the Swift was built, observers assumed that the Edens Expressway, the main northwest artery connecting Chicago to the suburbs, would be able to handle the additional traffic generated by former Chicago North Shore riders. There simply wasn’t enough interest to justify a new rail service, especially one that didn’t take riders directly downtown (the Swift would connect them to Howard, the far north hub of the CTA’s rail service system). How could that appeal to workers headed to the Loop? And how could it make money? Conventional wisdom said that for the economics to work, train systems with rush hour capacities of 10,000-40,000 were required. The Skokie Swift, running with just a handful of cars, was expected to have a capacity of 1,500.

But Krambles saw things differently. In an article in Railway Age, he said it wasn’t necessarily about operating in an area of high-density. The real test would be ease of use, and if the Swift could truly live up to its name.

The proposed transit test brought together a unique trio: a federal agency looking to improve transit, a city rail system experimenting with expansion, and a suburb grabbing at the chance to maintain a rail connection to the city. Funding for the concept was split between the three parties—$349,217 came from the Department of Housing and Development, $1,837,415 from the CTA, and $37,193 from the village of Skokie. At the conclusion of a two-year test, the parties would figure out next steps.

Between 1963 and spring of 1964, a new wooden station was built in Skokie, along with a park-and-ride lot for commuters, while the CTA created specially designed rail cars, with a unique “pan-trolly” system designed by Krambles that allowed the line to switch between “third rail” power supplies (used by the CTA) and the overhead power lines hanging over the abandoned rail line.

When the Swift service started operating on April 18, 1964, CTA Chairman George DeMent declared it would usher in “a new era in urban transportation.” Optimistic projections for the weekday rail service capped out at 1,500 riders per day. But even the most optimistic observers didn’t come close to forecasting the public’s reaction.

After one day, the CTA logged 3,959 riders, and almost immediately added weekend hours. By early 1965, 6,000 riders a day rode the Swift (the CTA estimated that the service removed 1,000 cars a day from the highway). The CTA logged more than 3.5 million rides during the two year test period, and by 1967, the passenger load had grown 170 percent from already-high 1964 numbers, hitting a record high that year of 8,150 riders a day. Chairman DeMent told the Chicago Tribune that it was “a perfect example of how good rapid transit can induce motorists to leave their cars at home.” Not only did the service prove itself, it made a profit of $216,717 on revenues of just under $800,000 in its first two years of operation. At one point, the Feds actually asked for $250,000 of their funding back.

Why did the line succeed? In short, because it proved Krambles correct. The experiment became a national news item—American City Magazine called it “the answer to a commuter’s prayer”—because it provided a service engineered for suburban commuters.

First off, it was perfectly sited and easy to access. The park-and-ride lot attached the the suburban stop was huge, with capacity for 700 cars, and perfectly positioned, right off the aforementioned Edens Expressway, so it was easy for suburbanites from across the area to board. In 1964, Park-and-ride wasn’t a new concept by any means, but previously, lots usually were positioned where transit agencies could put them, usually small plots at the ends of existing rail lines, as opposed to where they would work the best.

But it wasn’t just a one-way service. As a 1968 CTA report noted, the Swift also aligned with the switch toward suburbanization of jobs. “A rapid transit extension into a suburban area can open up many job opportunities, a point of special importance to less advantaged residents of an inner city who cannot afford automobiles to travel to a new suburban plant.” This wasn’t just for suburban dwelling office workers sick of paying for parking; this type of service could become a catalyst for more regional economic growth.

The second reason the Swift worked was because it lived up to its name. The Swift was fast. The little car initially reached a top speed of 70 miles per hour, but normally ran at roughly 46 miles-per-hour. Krambles proudly called it the fastest mass transit system in the world, and others took notice. An October 1964 Chicago Tribune article compared the Swift to the then-new Tokyo Monorail, noting that the CTA line smoked it, running at 46 miles per hour as opposed to 32.8 mph. When was the last time a U.S, transit line was favorable compared to one in Japan?

Finally, the Swift was convenient. In a Railway Age piece that said the Swift was proof positive. CTA survey results showed the system wasn’t just hanging onto existing transit riders but turning car drivers on to the benefits of transit.

Roughly 40 percent of Swift riders were new to the CTA, and 83 percent of riders owned cars. Convenience, as well as consistent and reliable service, and the smooth switch to other CTA trains at Howard, were huge selling points. Even with the Skokie Swift costing more than traditional commuter rail services (roughly $26.45 a month, compared to $20), commuters were willing to pay for the convenience.

All parties celebrated the Swift’s success. After the two-year, trial, the CTA chose to continue running the financially sound line. The federal government had data and proof-of-concept that could be used for other systems across the country, and Skokie, which continued to grow, saw its first major condo project, Old Orchard Greens, go up in 1965. Even the notoriously conservative Chicago Tribune editorial page saw fit to praise the little line that could; in a 1964 editorial bashing the expansion of federal transit spending, it made an exception for the “astonishingly successful” Skokie Swift.

The Swift’s sudden success seemed like a bellwether for bigger things that first year. The federal government had just passed the Urban Mass Transportation Act, which Walter J. McCarter, president of the Institute for Rapid Transit, called “the breakthrough that has long been needed.” That same year, Georgia voters approved the formation of a mass transit agency for Atlanta, which would later become MARTA, and Bay Area Rapid Transit (BART) broke ground. The CTA’s 1968 report on the experiment summed up the feelings of many, noting the line’s success in a paper titled “Skokie Swift: The Commuter’s Friend.”

So, what happened?

In short, the experiment wasn’t replicated. As some writers at the time noted, other Chicago suburbs could have set up similar lines, and even had the abandoned rail lines to do it; the Chicago, Aurora, and Elgin Railroad, which ran through western suburbs such as Wheaton and Glen Ellyn, lay dormant beginning in 1961 (to be fair, the line was eventually turned into the Prairie Path, a wildly successful rails-to-trails conversion). In the late ‘60s, Skokie voters rejected a bid to apply for a federal transportation improvement project.

Perhaps most importantly, during a period of highway expansion and urban renewal, the money wasn’t there, and additional capital for building such systems from scratch was hard to come by. Just look at the 1967 federal transportation budget. Of the $5.35 billion spent, only $160 million, or 3 percent, went to transit. As Joe Asher, a writer for Railway Age, wrote in 1968, “the streets and highways of U.S. cities suffer arteriosclerosis, the urban population chokes on auto exhaust, and one downtown after another gets chopped up to make room for new spaghetti-bowls of highways.”

Decades later, the Swift still lives on, an anomaly as opposed to a true trendsetter. Data collected from the initial experiment was used to design other light rail systems across the country, according to Graham, which riffed off the idea of quicker speeds and more spaced-apart stations engineered to get suburbanites to the urban core. Even to this day, he says the Swift still has a great cost-recovery ratio.

While the system has undergone some changes since it’s its ‘60s heyday—losing weekend service due to an all-system service cut, adding a station at Oakton—it’s mostly the same line. Some extension have been discussed, including one to the nearby Old Orchard Mall, but nothing on the table today has progressed past the early planning stages.

“Whatever the ridership changes may have been, it’s still considered a success,” he says. “Sunday was added back 10 years ago and it’s running strong. It’s an indication of the CTA’s commitment to this line.”

The Swift has slowed down, literally and figuratively. In a 1994 Tribune article, Krambles said the top speed of the Yellow Line had been cut to 55 mph as a cost-saving measure to help reduce the frequency of train maintenance. At that time (and this was before the Oakton Station was added to the existing route in 2012), Krambles guessed the average speed at 37.5 mph. But—and you can only assume he was pretty proud to say it—he said that was still enough to keep the title of world’s fastest urban mass-transit line.