"In tunneling tradition," the SFMTA writes, "the custom of naming [tunnel boring machines] is believed to bring good luck to tunneling projects." That's why the TBMs that dug the Central Subway tunnels were named after SF notables “Big Alma” de Bretteville Spreckels, and Dr. Margaret “Mom” Chung.

Sadly, however, that good luck does not extend to the machines, themselves. For now, purpose served, both TBMs are being savagely ripped to bits.

"To retrieve each TBM," the SFMTA writes on their Central Subway blog, "the machines are cleared of debris, cut into sections, brackets re-wielded for attachment points, pieces hoisted out, and parts are loaded on trucks for off-hauling."

Lest we forget their sacrifice, the above photo shows the Central Subway's northbound tunnel sitting empty after Big Alma was removed. On the right, Mom Chung continues to be disassembled, piece by piece.

The Central Subway, the SFMTA says, will be open for business some time in 2019.