I found that it's quite easy to place bridges in this way.
Make sure the points where the brigde is connected are at same level and it also makes it easier if the sea is flat (see the pic).
The bridge is 50 meters long so place it in the middle of the square. (The x-coord doesn't have to be in the center but the bridge should be just on one square horizontally. My bridge is in north-south direction, if yours is in west-east then just swap the coords). In the case you didn't know that every square in the editor is 50m x 50m so the coords of the center of every square end with 25, for example x=2225 and y=4125. Then place the next piece and set its x-coord to the same as the first one and add (or substract) 50 meters to the y-coord. Repeat this for all pieces and they are perfectly aligned.
Still they are vertically messed up and I don't better way so I fixed them manually piece by piece with the object position tool. First set the land parts so that they connect the bridge smoothly and then the rest. You have to estimate the proper height because the parts are aligned to the ground. Don't mind what it looks like in the buldozer because it will be fine in the game as said already. I had to adjust my bridge about five times before I got it in the way I wanted.
You can connect the roads easily by placing the terminator to the bridge x-coord and y-coord + 25.
I hope this helped at least somewhat...
I know it's not very fast way but at least I got my bridge working. Â
By the way, I don't know I you're already knew this but the smaller bridge located in the data3d.pbo doesn't work with cars, at least for me. Anyway it looks more like a pier than a bridge.
Oh and I forgot that if you change the height of the terrain near the bridge, the parts will lose their positions so you have to open the object position dialogue and then just press OK.