Do we know if undergrounding is even economically feasible? My gut says no. If undergrounding were hypothetically made mandatory, my guess is it would no longer be viable to serve a lot of customers out these 1.5 lane roads on 5 acre parcels.
Many of these lines have been here for 50-100 years. My assertion is that the unmitigated brush growth and refusal of small landowners to do anything about it is one of the major factors leading to this situation.