I both bike and walk on Broad St. several days a week on my commute downtown from Cerro Romauldo. A few observations and comments:
* City data show that the 85th-percentile speed is 31 mph, meaning about 1 in 6 cars goes faster than that. Of course, the trip from Ramona to 101 is not at a steady speed, but multiple accelerations and decelerations, stopping at the stop signs and gunning it in between. A "slow flow" street that has less full stops but is traffic-calmed to bring the 85% speed into, say, the low 20s might be better.
* Broad St. both parallels and crosses Old Garden Creek. This presents a big opportunity for traffic calming that also treats stormwater, reducing creek runoff pollution and lowering flooding risk in heavy storms and future El Nino years. For example, curb extensions would improve conditions for pedestrians, dampen turning speeds, make sight distance better at intersections, and help the City improve access for persons with disabilities.
Broad Street could therefore serve as both a bike boulevard and a "green street". For inspiration, one need not look further than Paso Robles: they won a US Green Building Council award for their 21st St. project. A Broad St. design would be different, but it shows that this type of innovation is achievable. One of the key intersections to look at would be Murray, which is literally on top of the creek. The downhill approaches also seem to encourage faster auto speeds. Also, since the sidewalk on the west side ends south of Murray, this is a pedestrian crossing area.
* The "green street" idea also touches upon another observation: many of the homes along the street have beautiful front yards. Many homeowners clearly put a lot of care and effort into landscaping, and the street itself could be an aesthetic complement. Cities like Portland have become seasoned at putting attractive, low-height plantings in their stormwater-filtering curb extensions. Another idea is widening the sidewalk at pinch points (e.g. where there are power poles) and adding a buffer strip, which could also be designed to filter stormwater.
* Finally, it is important that the bike boulevard cater to different ages and abilities of cyclists. This is a popular route to school, in addition to being a popular commute route.