It's there on version 7.7.0. What device are you using? On my Nexus 5, on the Search bar at the top, tap on the arrow icon. This brings up the Navigation screen, with options for car, transit, bicycle, and walking at the top (in icon form).
Oh yeah, I see that now on my Nexus 7. Weird. Maybe they figure that a person with a tablet isn't going to be riding their bicycle with it, but that seems odd considering that a 7" tablet is perfectly portable. I'd submit that to Google as a bug. Just tap on the "Send feedback" option. I'll do the same.