Ian
It depends on how wide wide is. In most cases if a fairway is 60 yards wide I would think an 80 yard wide corridor is ample if there are fairly large trees about and less if on open land. However, it seesm to me that more often we may see fairways 30-40 yards wide with an extra 20 or 25 yards for the corridor. It all depends on what the buffer is between the fairway and the edge of the corridor. In my experience, almost every course I see is a combination of one or more of the following: fairways too narrow, corridors too narrow, trees not kept properly trimmed, rough not properly maintained, tree undergrowth not properly maintained. The more harsh the buffer zone or edge of corridor, the more width should be required. If wind or sloping terrain is involved an extra 20 yards of fairway width (and hence corridor width) or light rough buffer is often missing. Links in the GG&I are often described as wide when in truth for most of the big guns (read championship courses or wannabe champiosnhip courses) this is not true in relation to the penal rough and bunkering.
Ciao