> If the lines were buried, there'd be less maintenance caused by weather events, less transmission losses, and overall more efficient and resilient operation.
It's a tradeoff. When there is an issue with underground lines, it's much more expensive to locate and diagnose the fault and repair it; in both dollars and time.
In that area of the country, the ground freezes in winter, and digging becomes very difficult, which would make repairs that much more delayed and expensive.
Also, depending on requirements, it may be possible to augment capacity ny adding a second transmission line to the existing towers at a later time; that would be much less expensive than setting up the first line; but for undergrounding, such a project would most likely be as expensive as the first time, if not more. Similar with replacing the line at the end of its service life (although if the line and the towers have a similar service life, replacing them both brings costs back up similar to the initial project)
It's also quite common for above-ground transmission lines to be upgraded: swap the fixed supports for carrying wheels, hook up the existing conductor to a bigger or more modern one, and pull it through! An older line can get a nice 30% upgrade at very little cost this way.
> In that area of the country, the ground freezes in winter, and digging becomes very difficult, which would make repairs that much more delayed and expensive.
Could underground lines be placed in tunnels large enough for repair crews to reach where they need to work by going through the tunnel?
Well, I'm sure they could for runs that aren't too long, so perhaps the question should be over what distance is it economically and technically feasible to run underground lines in tunnels human accessible maintenance tunnels?
It's a tradeoff. When there is an issue with underground lines, it's much more expensive to locate and diagnose the fault and repair it; in both dollars and time.
In that area of the country, the ground freezes in winter, and digging becomes very difficult, which would make repairs that much more delayed and expensive.
Also, depending on requirements, it may be possible to augment capacity ny adding a second transmission line to the existing towers at a later time; that would be much less expensive than setting up the first line; but for undergrounding, such a project would most likely be as expensive as the first time, if not more. Similar with replacing the line at the end of its service life (although if the line and the towers have a similar service life, replacing them both brings costs back up similar to the initial project)