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I would think putting up signs might be a good start.

Just kidding, I'm sure you have enough of those.

I imgine what you meant to ask is how to manage the huge amounts of traffic that's going on? Well, you may need to draw some comparisons to cities with comparable densities (Hong Kong, Singapore, London, Shanghai) and try to make use of systems that have proven useful there. One solution may be to close certain streets down entirely for motorvehicles without a delivery permit, and encourage more bicycle traffic.

flyovers only can solve this problem