A method and apparatus for forming a tunnel structure at a relatively shallow depth from the surface, which tunnel can be used as a replacement or additional transport route to an existing transport route (2) which is already formed on the surface. The method comprises the steps of forming two spaced apart access tunnels (hatched portion) to expose the tracks, introducing units (22) comprising side walls portions (26, 28) and a roof section (30) by moving the units along the tracks while excavating the soil in which the tunnel is to be formed is in advance of the leading edge of the units.