Tunnel
A tunnel is an underground passageway.
Tunnels are one of a number of asset types considered to be Essential Public Assets by the Australian Commonwealth Government.
Data Standard for Road Management and Investment in Australia and New Zealand
Section 8.3.31 of the Data Standard for Road Management and Investment in Australia and New Zealand defines a 'tunnel' as an underground roadway, dug through the surrounding soil and enclosed except for the entrance and exit.
It also lists a range of attributes that can be used when collecting data about tunnels.