I'm not sure if this is in writing anywhere, but based on my experience here is my definition:
Short Spans: 20-600 feet
Please keep in mind that the Federal Government defines a bridge as any structure with a clear span of 20 or more feet. Thus the lower limit. The upper limit is clearly an example of multiple short spans constructed continuously over that length.
Medium Spans: 500 to 1100 feet
There will always be some kind of overlap as the larger structures tend to be less economical over the smaller distance. For example at the 500 feet distance, a tied arch bridge would be less economical than a continuous plate girder bridge.
Long Spans: 1100-3000+ feet
In this category lie all the beautiful suspension bridges of the world. The lower end of this category is dominated in recent times by the cable-stay bridge.
