Bridges
From Captain of Industry Wiki

Bridges were added in Update 4, and currently come in two variants, Truss Bridge and Cable Stayed Bridge. They provide a means to connect islands over water, or as an elevated route bypassing a valley below.ds
Lanes
Bridges can have their lanes changed at any time with no cost. There are 4 types of lanes that can be applied:
- Left-hand drive 2-way small road (Pickups, Trucks, Small Excavators and Excavators)
- Right-hand drive 2-way small road
- 1 lane rail
- 1 lane electrified rail
There is no lane variant that allows Amphibious Trucks, Amphibious Excavators, Haul Trucks or Mega Excavators to cross a bridge.
Bridge Building
Bridges can only be placed along a specially aligned grid, 8x the normal tile, displayed when building a bridge. Whilst building a bridge, the tooltip information displays 3 pieces of information: height above sea level, current height above ground or seabed, and max height bridge is capable of.