Google Maps has rolled out a map layer and directions for bicycles.
Clicking the More... button and selecting Bicycling will reveal cycling features as different types of lines:
- Dark green indicates a dedicated bike-only trail;
- Light green indicates a dedicated bike lane along a road;
- Dashed green indicates roads that are designated as preferred for bicycling, but without dedicated lanes
Also, when you get directions you can now select Bicycling as the mode of travel (as seen below). According to Google the algorithm will prefer bike paths, lanes and slower less congested roads as well as avoiding hills (which you can override by dragging the route to other streets).
Official Google Blog post about bicycle features
Sample map of San Fransisco with intro video