The middle of the three pedestrian paths that are part of Still Street that. Between Lyell Street and San Jose Avenue/Tingley Street, each block Still Street alternates between being only a pedestrian path and an actual street.
Still Street itself was created when Interstate 280 was built in the 1960s, shortening the streets north of Cayuga Avenue.
Until the early 1990s, there was a long pedestrian bridge over Interstate 280 and San Jose Avenue from the intersection of Diamond & Monterey that came down next to this path at Lamartine Street. I'm not sure why it was removed, although the timing suggests that it could be related to the Loma Prieta Earthquake. Maybe it was damaged, or determined to be seismically unsafe. It could have also been over crime and safety concerns, which is the same reason the bridge over 101 near 25th Street has been closed for decades.