If you click on a section of the generated route a dialog box will appear allowing you to rate that section's perceived safety on a scale of 1-7, this will affect future generated routes. Also the system tends to prefer residential streets and cycleways over major roads, and prefers roads with bike lanes or signed bicycle routes.
OpenStreetMap
Discussion
Comment from wieland on 22 March 2010 צו 08:58
How do they know, which way is safer?
Comment from andrewpmk on 23 March 2010 צו 03:51
If you click on a section of the generated route a dialog box will appear allowing you to rate that section's perceived safety on a scale of 1-7, this will affect future generated routes. Also the system tends to prefer residential streets and cycleways over major roads, and prefers roads with bike lanes or signed bicycle routes.
Comment from wieland on 23 March 2010 צו 21:06
@andrew: Thanks