Tunnels become unavoidable for negotiating hills, where detours are costly. The tunnels in rock are not lined, but those in loose strata require a lining of cement concrete. Drainage of water should be taken care of. Railway tunnels do not need to be lighted whereas road tunnels are invariably lighted.
Laying of Track
Laying of a railway track is also known as plate laying. It is the normal practice to lay the sleepers initially directly on the embankment and fix the rails to the sleepers, without placing the ballast. This is done so that the track can settle in the initial stages when the embankment is still in a loose state. Ballast is packed subsequently. The track already laid is used for transporting fresh track material on wagons.