Just to dive into this a bit more. I just got quotes to connect three of the farms on our campus.
$3.50/ft over the distance of about 15 miles for ariel. That includes sinking new poles, putting up the wire, purchasing right-of-way, etc.
> $900/ft over the distance of about 15 miles for buried. That includes concrete encasement, conduit, purchasing right-of-way, road construction and the engineering. We would also need power vaults every few miles for transformers and equipment to load the line properly.
So, in places where space is a premium and it's nearly impossible to have ariel (think of a downtown area like Chicago, NYC or LA), it makes perfect sense to bury. For other times the cost really is prohibitive. In a small downtown area with a very dense area there is justification to do it. You do gain some reliability, particularly from wind/snow/ice/car/hunter damage, but you lose some reliability if your undergrounds flood/overheat/catch fire. The chances of the undergrounds misbehaving are a lot less, but they still exist.