I hear you about the lakefront bike path, but I fortunately now live
at the north end (like all the way up by Hollywood) and I have to say
it's FAR less crowded up there. If you're already willing to make a
trek, you might try driving a bit further north. Finding a good 10
mile stretch (or even 5 that you could loop back on will prove hard
though). My other 2 suggestions are also based on where I used to live
in the city. There's a great path along the river (again further
north) that my wife used to walk when training for the breast cancer 3-
day. I believe she used to start around Lawrence and walk north from
there. And I grew up kind of near(ish) Caldwell Woods which has a
wonderful walk/bike/run path that goes all the way north to the
Chicago Botanic Garden - it was never that crowded and I always felt
safe biking it when I was younger.