I live in Minnesota, and a few years back, Excel Energy constructed a massive power line stretching from Monticello, MN to Fargo, ND.
This is not the exact photo of the power lines, but it's very similar in design:
The power line is wired on only one side of the tower for the entire trip of the line. The only exception is when the power line crosses Highway 94, both sides are wired. Once the line has crossed over the highway, it continues on only one side. The line crosses several times for the length of the trip (approximately 200 mi,) each time, both sides coupled.
My question is, what is the purpose of having both sides of the tower completely wired when crossing the interstate when only one side is clearly being used? Are these "extra lines" underground cables that need to be crossed overhead?