This is a single-track tunnel with portals at both ends based on the tunnel under the Liverpool Range at Ardglen, NSW.
To install this tunnel, run a no-ballast track spline underground on the tunnel path. Then run this spline along the same path and adjust the height at spline points to leave only the tops of sleepers visible. Add spline points along its length if additional adjustment to the tunnel's gradient and/or curvature is required.
Use matching asset '<kuid:368725:20550> Ardglen tunnel portal dighole cover' to close gaps at the sides of and above the portals.