Fairfax County supervisors on Monday narrowly voted to let a Saudi-funded Islamic prep school expand its campus on a hazardous country road, capping a months-long debate that mashed traffic concerns with accusations that the school’s curriculum fosters religious intolerance.

The Board of Supervisors, in one of the most delicate decisions in their recent history, voted 6-4 to approve a construction project that would expand the Islamic Saudi Academy’s 34-acre property on Popes Head Road in Fairfax by roughly 230 students. It currently has about 270 students.