Google Maps API V3には早くも自転車のルート検索が追加されてる！

Google Maps API V3 Reference - Google Maps JavaScript API V3 - Google Code

DirectionsTravelMode class

The valid travel modes that can be specified in a DirectionsRequest as well as the travel modes returned in a DirectionsStep.
Constant
Constant Description
DRIVING Specifies a driving directions request.
WALKING Specifies a walking directions request.
BICYCLING Specifies a bicycling directions request.

日本の地図で使えるかな？