It’s beginning to look like the L train is the MTA’s test line of choice for system enhancements. Earlier this month, a few L trains were spotted with the agency’s new fold-up seats, which are being introduced in hopes of fitting more passengers onto trains—which may, by extension, alleviate rush-hour congestion.

And now, another enhancement may be on the way: According to the New York Post, the MTA will test out floor-to-ceiling platform doors, which are intended to prevent passengers from falling (or worse) onto the subway tracks. Such doors are already in place in some global subway systems, including in Paris and Seoul. (And if you’ve ridden the AirTrain to JFK, you’re already familiar with the technology.)

The doors would be installed at the Third Avenue station in 2019, during the forthcoming L train shutdown, and could make their debut when the line reopens in 2020.

There are some barriers to a system-wide roll-out, namely the fact that many of there isn’t much consistency to the sizes of stations (making a design that can work throughout the whole system tricky). There’s also cost to consider, an issue the MTA has been struggling with for even its emergency action plan.

But to some transit advocates—and even the architect of the AirTrain station—it’s an idea that’s long overdue.