If you browse the image search results for "china high speed rail viaduct" it's obvious that it's a lot less disruptive than laying the track at surface level.

If you browse the image search results for "china high speed rail viaduct" it's obvious that it's a lot less disruptive than laying the track at surface level. E.g. if it's through the middle of your field you can cross the track at any point, as opposed to going out of your way to get under a tunnel. Most of the land underneath the track can still be farmed, so why wouldn't it be cheaper?