The Castro Shuttle, also known as the "S" line, is back. 

As of Monday, two extra one-car trains are now running during the weekday morning rush hour, making about 10 total trips to provide additional breathing room for Muni Metro commuters from West Portal to Embarcadero stations.

Previously, riders at those stations were often out of luck, as inbound K-Ingleside, L-Taraval and M-Ocean View trains are often too overcrowded to admit new riders by the time they reached West Portal. 

The Castro Shuttle was originally introduced in 1995, but by the early 2000s, the number of available trains dwindled due to vehicle maintenance challenges, and Muni put the service on pause.

In recent years, some riders might recall seeing the Castro Shuttle make occasional appearances for major events, like Giants games at AT&T Park. But this is the first time in years that the Shuttle will be available indefinitely, Muni spokesperson Paul Rose explained.

"Adding 'short trip' trains like these is a strategic way to use limited resources, to provide more service where it’s needed most," Rose said. 

ATTN: Castro Shuttle is now approaching Castro station.

— SFMTA (@sfmta_muni) November 9, 2016

The new Castro shuttles come on the heels of Muni's addition of N-Judah trains from Cole Valley to downtown during the morning rush, which were added in September and have met with approval from many riders. 

There's only one problem with the new addition: the S line is not on any of Muni's station signage, and as a Twitter user noted, many people are not boarding the new trains because they're not clear on where they'll go.

Rose said that Muni personnel in the stations can help, and that the agency will also announce when the Castro Shuttle is arriving on Twitter. But with no signage changes pending, if you see hesitant fellow commuters avoiding the "S" trains, take a moment to let them know where the trains are headed. 

How has your experience with the new Castro Shuttle been so far? Let us know in the comments.