CHICAGO — Like New York’s subway, it is another century-old system struggling to keep up with the transit demands of a booming city. It, too, has been plagued by crumbling tracks, antiquated signals and unreliable trains that turn routine commutes into nightmares.

But the difference is that Chicago’s L has made a comeback, reversing decades of cost-cutting and neglect.

Today, nearly one-third of its tracks have been rebuilt for faster and smoother rides. Rail cars from the 1970s have been replaced with the latest models. More than three dozen stations have been overhauled, many rebuilt into sleek, steel-and-glass outposts. There are new elevators, wider platforms, high-definition security cameras and works by Chicago artists.

“We’ve had a pretty impressive turnaround,” said Joseph P. Schwieterman, a professor of public service at DePaul University. “It’s still an old system — and we still have delays — but the problems are staying out of the headlines and that’s quite an achievement.”