In the case of a truss bridge, a post-tensioned slab bridge, or a box girder bridge the sections are often floated to the bridge and then lifted into place by cranes on barges or cranes sitting over piers.
The very good reason why the word communism is so commonly associated with these revolutionary, anti-liberal, anti-democratic Marxists is that political parties with communist in the name were pretty much invariably of that bent throughout the 20th century, whereas parties called socialist or social democrat or labor varied enormously in ideology.
At one time, there were many such countries, and it seemed as though communism would win. But communist party governments forgot to use democracy in their governments, a very important part of socialism and communism. Because of this, the governments became separated from the people, making communism difficult.