During construction of a tunnel it is often convenient to install a temporary railway, particularly to remove excavated spoil, often narrow gauge so that it can be double track to allow the operation of empty and loaded trains at the same time.
It is often convenient to install a temporary railway, particularly to remove excavated spoil gauge so that it can be double track to allow the operation of empty and loaded trains at the same time. This is during construction of a tunnel. This is often narrow.