Maybe 3 rows of Virginia pines planted 4 feet spacing.

This doesn't apply to the OP since he said the land borders a county road, but we are learning a lesson about private roads. Years ago, the landowner planted pines along the road going into the property. At one time, this was a county road. I can't recall if the pines were planted before or after they county allowed the owner and neighbors to make the road private. Anyways, now the pines are mature and the road is terrible. A young man knowledgeable on such matters told us that the pines block the sun and don't let the sun dry the road out. Makes sense to me. The shame of it is that they cut a lot of the pines last year and could have taken the ones along the road if anyone had known that is what is causing the problem.