> The underground are not tunnels but excavated with the road built on top, Are you describing "Cut and Cover" ? As in "Cut and Cover is a method of construct

> The underground are not tunnels but excavated with the road built on top, Are you describing "Cut and Cover" ? As in "Cut and Cover is a method of construction of shallow tunnels" https://en.wikipedia.org/wiki/Tunnel_construction#Cut-and-cover https://en.wikipedia.org/wiki/Tunnel_construction#Cut-and-co... It has been used for centuries, e.g. was used to dig the first parts of the London underground in the late 1800s