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Determining a Practical Bridge Design for a Wide River and Heavy Traffic

Hello everyone, I am thinking yet again about infrastructure. (my calendar project recently asked about... well, that's outside my expertise, I'll get back to that eventually)

And I am thinking of the limits of just how much a bridge can do.

So, some backstory. This main bridge (along with 2 others, many kilometres away, with much less load on them) joins a large city on the northern side with its brooklyn/queens/new-jersey suburbs on the other side, and this city is LARGE. The city is, let's say, 80-95% of the population of Tokyo. The river is very wide, nearly as wide as the Hudson River in NYC, and **I'd like to retain as much shipping width as possible.**

I would like to run a 6-track mainline railway across, plus a 6-track metro line(multiple "lines" would use it), and finally a 6-lane highway.

But, looking up the longest bridges, not many have anywhere near this much load on them. Which isn't great, because this river is a internationally important shipping channel that carves through a mountain range and provides very cheap bulk freight to a mediterrainian sea. And due to some locks constructed, **this entire river must remain at least panamax**, but a larger span is needed here due to the business of the ports around the bridge

So, how would I make a 500 metre bridge? In reality, would this just be done as three parallel bridges, each carrying a different type of vehicle? Or would one massive bridge be done? 

And if it were to be 3 separate bridges, how strong would the 6-track mainline bridge need to be, assuming heavy north american-like weights? (they use a wide track gauge, and some double-decker EMUs would be weighing a bit more than a pullman heavyweight...)

So, to summarise what I am asking: 6 traffic lanes, 6 mainline railways, 6 metro lines, **either** all in one bridge or all in separate bridges. 
Bridge must not block shipping in the busy river below, so should be near to 500 metres main span length. How possible/feasable are these options?