they are called Sharrows - shared arrow markings.
They are used to indicate to drivers that this is apreferred bike route and to emphasize that the street is to be shared with bicyclists. Where the markings are right in the middle of the travel lane, they are combined with this sign,
"Bike May Use Full Lane" to emphasize that bikes are allowed to use the entire lane, the same as a vehicle. This combination is used on preferred bike routes where the travel lane isn't wide enough for bikes to ride side by side with vehicles.
The first photo above shows 4th Street from Montgomery toward Main Street. On-street parking is allowed on the left side of the street only. The rest of the street isn't wide enough to incorporate a 5' wide bike lane and still have enough room for a vehicle to travel safely. Instead, sharrows were used to indicate a safe bicycle riding location that also allows for a large enough gap between them and passing vehicles.
On other parts of 4th street, namely between Gorman and Talbot, sharrows are placed 11' from the right curb. This location guides bicyclists to an area that prevents them from getting hit by opening doors from cars parked on-street along the right side of the street, yet still allows for a comfortable separation distance for vehicles to pass on the left. See photo below.
|Sharrow on 4th Street between Gorman Ave and Talbot Ave|