Raise tolls, promote remote work unless you absolutely need to be in the city. Use economic incentives to destroy demand for unnecessary vehicular travel.
I am with you, but we don't have infrastructure for toll collection on most of the East River bridges, so there isn't an easy answer here. (A lot of the traffic on the East River bridges is trucks that are simply avoiding the more direct tolled truck routes. It's unfortunate that CO2 emissions are cheaper than tolls, but here we are. I live in Brooklyn Heights which is walking distance to Manhattan modulo a big river in the middle, and I know my neighbors are just going to start driving to work when things reopen. It is going to be a mess.)
London managed it with congestion charges, and it is not an island with limited entry/exit points. No toll booths required: it is doable within a reasonable timeframe.
