I came across a guy a few years ago that had crashed/fallen and managed to break his leg. I didn't see it happen and somebody else was already helping him. It might have been in the winter actually. At that particular spot, at that particular time, he wasn't in any real danger. There's a lot of car and people traffic around.

However, there are some pretty popular commuting routes like the Cedar Lake trail that take you from downtown through some open fields and woods to the Southwestern part of the city and the Western burbs. If you were to bite it in some wet snow and were hurt in the process, it could be awhile before somebody found you, - again depending on the time of day and the weather. There just aren't as many people on the trails this time of year.

On the other hand, most everybody carries a cell phone these days, so I wouldn't think help would ever be too far away. It could be pretty miserable waiting for them though.