I found myself in a similar situation not long ago. Was driving along a country road, hundreds of miles away from where I live, had no real idea where I was (just following SatNav instructions) and came across two pheasants, just a few feet away from each other, in their death throes on the road. They'd obviously been hit by a vehicle and were in a very bad way.
I said to my OH, we'd have to stop and help them but I couldn't bring myself to go back and run them over (to end their suffering) and neither could he.
Had no idea where the nearest vet was, but suspect they'd have died before we could get them there anyway. We drove on and left them and I feel incredibly guilty about this. :o(