Good point. If we need to stop at an "Improved Access Facility", say to use a pit toilet located within that facility (Wow, a pretty important stop), we would be required to have a permit otherwise we will not need one for exploring backroads or using facilities outside the improved access area.
Permits apply to all "Improved Access Facilities", a clearly identified area specifically created for motor vehicle parking, i.e. boat launches, RV parking sites, trail heads, etc.
Washington Department of Fish and Wildlife Vehicle Use Permits are the equivalent of the Northwest Forest Pass issued by the Forest Service.
Proceeds from permit sales are used to maintain facilities and remove garbage, a never ending problem and expense. Annual WDFW permits cost $10.95 and can be purchased wherever hunting and fishing licenses are sold. Annual NWF passes cost $30.00 and are available at Forest Service offices and several retail outlets.