Here’s video of the detour the City of San Jose wants cyclists to take while the Guadalupe River Trail is closed for construction work.
This is San Jose First Street between about Montague Expressway and going south to Hedding Street. In this video I don’t turn down Hedding but I do point it out. First Street is doable but it’s not exactly a pleasant ride, especially compared to the completely traffic separated GRT. There’s been discussion on the SVBC discussion list in the past that cyclists get a little more harassment from motorists (shouts, honks, thrown objects, etc) on 1st Street than probably anywhere else in San Jose.
There’s some discussion here about other alternatives people plan to take while the city paves this trail beginning in June 2012.