Try to find where they are entering and exiting the road and setup there away from the road. If its legal in your area, and little or no traffic is on this dirt road then you could set off to the side 20yards or so shoot the birds as they cross in front of you. If a bird is standing in front of you there obviously isnt a vehicle in close proximity. However never shoot down the road. I setup on logging roads like this quite often. I have seen birds walking down a logging road and when a vehicle approaches they run into the woods a ways and stop. ONce the vehicle passes they work their way back out to the road.