I now know why all the of initial ADA ramp projects were on 21st Street. That is the first street being repaved as part of the Central City Mobility Project. 21st has been identified in the project for separated bikeways. Since there is a bus route on 21st (SacRT Route 62), I assume that the bus stops will be on the right hand side northbound, and the bikeway on the left hand side. The design shown on the project webpage shows a parking-protected separated bikeway on the left, along with a buffer zone (to protect against car doors opening). This seems to be the standard that the city has adopted, and side so far the city is placing separated bikeways only on roadways that also have bus service, presumably this design will be used in every case.
Another diagram indicates that there will be vertical delineators (K-71) in the buffers, but there are no details about the frequency. There’s are the delineators that are run over and destroyed by vehicle drivers on a regular basis, and these will suffer the same fate. The larger diameter delineators (NOT bollards, the city is incorrect in calling vertical plastic a bollard; bollards are made of metal or concrete, not plastic) that are now installed on part of J Street are not specified here. Though these don’t provide any more actual physical protection, they seem to raise doubts among drivers and get run over less often.

There were several curb islands along 21st Street on the left hand side. All but one have been removed. The remaining one at 21st Street and Capitol Ave may just be an oversight, but if not, it is in the middle of what is expected to be the separated bikeway.

The fourteen blocks of 21st Street from W Street to H Street has been stripped down about two inches, for repaving. The restriping after paving will include the separated bikeway.
The project webpage has a diagram for the transition of a separated bikeway on the left side of 19th Street southbound to the right side of 19th Street south of W Street, which is a two-way street. However, it does not have a diagram for the transition of this 21st Street separated bikeway at the north end, where 21st Street becomes a two-way street at I Street. This is already a hazardous intersection due to the double left-turn lane from 21st Street to I Street westbound.
Separated bikeways are only as safe as their intersection treatments, and the transition from and to separated bikeways to regular bike lanes are critically important. I hope that the city has a good design for 21St Street and H Street, otherwise bicyclists will be placed in more danger than existing conditions. The solution is of course bicycle signal faces that allow bicyclists to move when other traffic is held, but the city has been reluctant to use these.
On the corners at 21st Street and I Street, there are strange posts installed. Patches in the pavement and sidewalk indicate that there is wiring to the posts, but there are no cutouts in the posts for the wiring. Are these pedestrian button posts? I hope not, because the city should not be installing discriminatory pedestrian buttons. Are there for audible signal buttons? Perhaps, but the city has installed these in few locations, and it is strange that they would be here. The posts are taller than is normally used for pedestrian buttons. Scratching my head. The last time I was at this intersection, several walkers were looking at the posts, questioningly, and we all shrugged our shoulders.

Lastly and sadly, a screwup on the part of the city. A non-compliant diagonal ramp is being replaced at a compliant diagonal ramp on the southeast corner of 16th Street and Q Street. Given all the work and expense the city has been going to to replace corners that are perpendicular and only needed the detectable warning strips, to neglect this one corner is ridiculous. This is one of the few corners in the entire central city with a diagonal ramp. And now it will be set in place for 30 years. Ack! What brain-dead engineers are in charge of this project?

The repaving of 21st St is complete, but new striping has not been installed. It appears that 19th St will be next.
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