The price to build something isn't at all related to what it would actually cost to build something. Two different concepts entirely, that you need to comprehend fully if you are going to work in government.
Actually, for a real answer you should ask
@EvilRoy. This is actually his line of work, if I'm not mistaken.
Uh, sort of yeah. People ask me this kind of stuff now and then and although I'm not much of an estimator I can shed some light on what is going on behind the scenes.
Without knowing which specific bridge this is or seeing concept art its tough for me to nail down the major factors but there are some usual suspects.
Off the hop I'm going to sadly tell you that there is not 1 million dollars of paperwork. My god, I wish that was the case. Its tough to nail down specifically what money goes to paperwork, but in general terms somewhere between 5-15% of the total budget will go to design, and then another 10% will go to management during construction, on the client side only. The contractor also dumps money hand over fist into admin but fundamentally in paperwork alone you're looking at burning roughly a conservative 10% of that 7 billion just on the owners side. This is all necessary, and more and more so the more complicated the bridge.
I dealt with a bridge that clocked in at just over 100 million and when we got all the paperwork together for design plus the first half of construction it filled my coworkers minivan. Just solid binders, and we had to stop because it was sitting pretty low on its shocks.
Otherwise in your estimate you have the right kind of idea, but your factors are off. You have people/equipment at about 2:1 to material. Its more like 4:1 to 5:1 - material is worthless compared to human time, often as a function of how it is worked with. Imagine a cubic meter of concrete. In order to place that concrete you need a small team to build a form, then guys to lay rebar, then guys to work the batch plant and deliver the concrete, then guys to place and finish the concrete, then you have to wait for it to cure. That's a small army for every bit of concrete - those are all different humans. Sure the cost of labour to cost of material goes more in your favour when you have larger quantities of material in play, but not as much as you would hope. Plus, machines are more expensive than you think. Large excavators can run tens of thousands a day, and you might need dozens of them to keep work going. Even things like rig mats - these are like steel frames filled with timber - are thousands each, and are brought to site by the hundred. Often you budget to destroy 10 rig mats a week if its during the wet season.
The last big thing you're missing is "site occupancy" or, more generally, opportunity cost. This is going to account for a huge chunk of the leftover money. Basically, whenever you do construction you crap up an area. Traffic slows down, people get in more accidents, the city fields more complaints, you have to work out legalities for land access (or even acquisition if you need to buy some lots up to be able to do this work), there are environmental tariffs, stores lose business, land values drop so taxes go down - its horrible really, building anything. In the advertised cost of a project a lot of time all this stuff will be included as a cost to the owner (local govt usually) because all this stuff will come back to the people holding the bag and somebody has to shoulder the cost eventually.
