While there's no word yet why a L-Taraval train derailed in the tunnel this morning, more than 20 bus shuttles are currently carrying Muni passengers between Van Ness and West Portal stations. All lines are affected. Appeal has word "that all Muni traffic is slow between Castro and Embarcadero stations," as well as the press release MTA just sent out. Ahem:

As of 11:45 a.m., the SFMTA has determined that the middle truck of the second car on the outbound L Taraval train came off of the rail by approximately one foot. A truck is a set of two axles and four wheels; there are three trucks on each LRV.

The K/T, L and M Lines continue to be directly affected by this incident. These lines are not operating in either direction in the Twin Peaks Tunnel between Castro and West Portal stations.

More than 20 bus shuttles are serving Muni customers between Van Ness and West Portal stations (making all Muni Metro stops in between).

There is slow traffic in the Muni Metro subway between Embarcadero and Castro stations.

There is no estimate as to when regular Muni Metro service through the Twin Peaks Tunnel will resume. An update will be provided before this afternoon's commute.

The derailment has damaged a communications loop that is part of Muni Metro's Advanced Train Control System (ATCS). This loop will need to be repaired before automatic service can resume through the tunnel. There is no estimate as to how long this repair will take. SFMTA staff is working to re-rail the train and inspect the track.

The cause of the derailment is under investigation by the SFMTA.

SFist commenter Be_Devine claims a fight broke out at the Castro Street station, reportedly due in part to Muni frustration. He tells us, "Cops were flooding into Castro station this morning reporting a fight on the platform. The furor of a delayed and pissed off queen is nothing to trifle with, so I chose to walk down to visit my old, reliable friend, BART." So, please, try to treat each other with a bit more patience today. Because you're all going to need it, Muni riders.