Just because a street is bikeable doesn’t mean you want to ride down it. Maybe there’s heavy traffic and no dedicated bike lane, or just a small lane made with painted lines. Not all cyclists are daredevils, and some, if given the choice, would prefer to ride only on dedicated bike lanes that provide some kind of buffer between you and the road. You might not be able to tell where those lanes are just by looking at Google, but Mapzen’s bike map color-codes streets not just by route, but by safety.
Spotted by FlowingData, the system uses OpenStreetMap to visualize the safest bike routes across a city, breaking them down into three tiers. Green paths, the safest, are off-road cycle paths or lanes physically separated from traffic (like bike highways). You might have to share with pedestrians, but you don’t have to dodge cars. The second tier, marked in orange, refers to the painted-line bike lanes you see on most roads, which are safe-ish but not entirely worry-free for many cyclists. The third tier, marked in blue, indicates roads with “sharrows” or other markings that mean that cyclists and cars have to share the road. The pink marks of the final tier show where you can’t ride your bike at all.
Unfortunately, you can’t get a route mapped out for you that automatically tells you how to get from one location to the other on the fewest number of unsafe routes—you’ll have to plot that course on your own.