Last spring, as Metro workers finished up months of work on the 29-year-old Blue Line’s southern tracks, the transit agency put up signs at the train’s newly revamped stations designating it as the “A” Line.

It was the first step in a plan to make LA’s rapid transit network more user-friendly—by giving letter names to all train and rapid bus lines.

Already, the Blue and Expo lines have formally been renamed “A” and “E,” respectively. Metro’s blog, The Source, announced Wednesday that the agency will start rolling out name changes on all lines in the coming weeks.

That means that the Red Line will be the “B” Line; the Green Line will be “C;” the Purple Line will be “D;” the Orange Line will be “G;” the Silver Line will be “J;” and the Gold Line will be “L.”

In general, those letter names follow the order in which lines opened. Because the Blue Line is the oldest of the bunch, it’s “A.” The Red Line opened second, so it’s “B.” The letters “H” and “I” have been skipped because they are often used on maps to denote hospitals and information points. The letter “F” was rather prudishly “not approved for use,” according to a tweet from Metro.

The Gold Line’s “L” moniker doesn’t follow the same naming convention; because the line will eventually be split in two and linked up with the A and E lines, its letter name will be a temporary placeholder.

The naming shakeup is aimed at making line names more consistent and ensuring the system is accessible to new riders. When the agency’s Board of Directors approved the new naming conventions in 2018, most of Metro's lines were named for colors (with the exception of the Expo Line).

Metro staffers had considered giving every line a color name, but found that could eventually get complicated as the agency expands its transit network and opens new lines over the next few decades (new riders might struggle to find the Green Line on a map that also includes an Olive Line or a Lime Line).

Under the new system, each line will have a letter name associated with a corresponding color, similar to the New York City subway system (though numbers won't be incorporated in some line names, as they are in New York).

A report from Metro staffers acknowledges that many riders will probably continue calling lines by their old monikers, but signs and maps will be changed to reflect the new naming system. The current color scheme will also continue to be used, meaning that the Blue, Red, and Purple lines will still appear on maps in those colors.

For now, Metro employees will also continue to refer to the lines by both their new letter names and the more familiar names they used to operate under. For instance, A Line trains are currently referred to in station announcements as “A Line-Blue” trains. Eventually, that will be shortened to the letter name only.

Still waiting on a letter name is the under-construction Crenshaw/LAX Line, which is expected to open in 2020. An agency memo suggests it will be the “K” Line, but The Source reports that a name hasn’t yet been finalized.