[HH_Blaze]

First of all, the bridges can only be set over water at sea level. Select the type bridge you want, place it on the map - this part can be a bit tricky, it seems that the "point" you choose is where the road meets the bridge incline, and must be place on a point where two black grid lines on the map intersect. Use the arrow keys to rotate (only at 45 degree angles), then Page Up to extend the bridge over the water.

Hope that helps you, gl with your bridges.