They're buying more than 12,000 of them, so it's not for all or maybe any underpasses. Less ballast and grading work in critical areas? Compared to only 6500 wood ties. 1500 of the wood ties are marked as for crossing approaches. I suspect the remaining 5000 wood ties will be used on the rehabbed bridges of which there are 3 and some critical areas where steel would not be appropriate perhaps for noise vibration and harshness reasons. It seems to me 12000 ties would cover about 2-1/2 miles, the amount of rail they are going to replace.