I haven't met that many bridge architects :D

But do they build bridges by themselves? Are bridges built by a one man show?

And they don't have rules? And how do they get anything done?

Are you sure you did read my previous comment? You are replying to stuff that isn't there.

About rules, no, nobody pass rules down the stream. People communicate full designs of some issue (that is not the full design of the thing, designs are "sectorial" where people add their concerns into the overall thing). When it's done right, the design goes to and from those sectors changing the entire time. When it's done badly, somebody finishes a "general" design and sends it downstream for people to fill the other parts. A team does not work on the same issue, that would be chaos.