According to the Fort Collins Traffic Code, there are three times when a person must dismount their bicycle:
1) If you’re in the dismount zone downtown.
2) If you’re in the dismount zone on campus.
3) If you’re anywhere else in town and there’s a sign indicating that cyclists should dismount. (This only happens very occasionally.)
Crosswalks are not dismount zones in the city of Fort Collins. The only rule you need to know when riding your bicycle through a crosswalk anywhere in town, is that “A person riding a bicycle in a crosswalk shall do so in a manner that is safe for pedestrians.” — from 2106(2)(a) in the Traffic Code.
And of course, any time you’re passing a pedestrian, no matter whether you’re on a trail, on a sidewalk, or in a crosswalk, it’s always a good idea (and it’s in the Traffic Code) to ring your bell or call out before passing. No one likes to be startled by someone zipping past unannounced.
Although downtown has a pretty extensive dismount zone, meaning that you’re not allowed to bike or board on the sidewalk there, it is legal to bicycle along any of the streets (including College Avenue) and in the alleyways.
The dismount zone at CSU is date and time specific. As you can see in the photo in the above slideshow, the dismount zone is only in effect Monday through Friday from 7:30am until 5:00pm.
As is often the case with transportation issues, there’s a certain amount of common sense that’s required. If you decide to ride your bicycle on a sidewalk that happens to be full of people and you end up running someone over or causing mayhem, then you can be ticketed for “reckless and careless riding” under section 2102 of the Traffic Code. So while it’s theoretically legal for you to be riding on the sidewalk in that case, it’s probably not a good idea.
To read the code directly, go to the section on bicycles and look specifically at Part 2106.