While I doubt that "Las Vegas tunnel is mostly under parking lots with no obstructions" is even close to represent reality, here's what Boring Company says on the subject:

> With a typical minimum depth of 30 feet, The Boring Company tunnels are well beneath most utilities, which are typically less than 10 feet below the surface. In circumstances where a utility is located deeper, the tunnel depth is increased accordingly.

From https://www.boringcompany.com/faq