android gmaps has turn-by-turn for driving and walking but not biking. for bike directions you can only see the route mapped out.

so I would just set it to walking directions. only two potential problems: 1) the view shifts to satellite, which is a little harder to see 2) it might send you backwards down a one-way street!

of course you could put it in turn-by-turn driving mode, which will probably be fine for an urban commute. just don't get on any highways :-)