General
All road types can be built or updated by units with engineering abilities;
Engineer,
Native Engineer,
Water Engineer, and
Hunter. No road can be built
on river tiles until Manufacturing
is known.
Road
Basic Road is available for building from the beginning of the game.
Movement via Road costs 2/3 movement points. Having Road on
Grassland tile provides
increase of +1 to trade on that tile.
Highway
You can update Roads to Highways once
Brute Force tech is known.
Movement via Highway costs 1/3 movement points.
Maglev
You can update Highways to Maglevs once
Maglev tech is known. Units can move
via Maglevs indefinitely. Shield production of any tile
with Maglev is increased by 50%.
Tunnel
You can build Tunnel once
Strong Resistance tech is known.
Earthly units can travel on radiating tiles with tunnel built on them.
Burrow Tube
Once Burrowing tech is known, you can
build Burrow Tubes to oceanic tiles. Burrowing units can use these tubes to
travel across oceans.