4 Hour rule= cross-utilization.
A "four hour rule" station is one where grey-book represented employees (read: CSA's) perform bothh the CSA functions and ramp functions.
The term comes from language in the CBA's that discusses ground times for A/C. Without going too far into the specifics, basically, if there's less than 4 hours of work in any given 8 hour period, then it's a 4 hour rule station. This is a bit misleading however, as many stations in this category handle many more flights (both airlink and mainline) than this, but only mainline A/C factor into the formula. On the other side of the equation, there are stations with ESE's that should technically be 4 hour rule (GEG, MSO, & RST come to mind)but have been grandfathered in.
Of the "80ish" stations NW wants to outsource, almost all of them are 4 hour rule.
Hope this helps...