In doing so, the Bord dismissed an appeal by anti-pipeline campaigner Micheál O'Seighin and An Taisce.
The expanded entrance, at Glengad Pollatomish Co Mayo, is allowed for five years, after which the entrance must be restored to its original state.
The Bord said it believe the retention would not have a significant effect on the Special Area of Conservation at the Glenamoy Bog Complex.
The order also stated that the development would be acceptable in terms of traffic safety and convenience.
The permission was granted subject to two conditions.
