Public Transport

Manhattan had car-sized streets, sure. But, they were used completely differently.

For example, vendors would come and park their carts on the side of the street, with the wares facing the middle of the street, and people would walk up and shop while standing in the street. There were a lot more people walking and standing in the streets. And, it was a lot more common (and a lot safer) just to walk out into a street, because a horse wouldn't typically run someone down, and when cars first came along they were very slow.

I don't really see super wide streets as being a problem. Especially in a place like Manhattan where there are huge skyscrapers, you want wide streets so buildings aren't in perpetual shadow. You just need to make sure to keep cars away, and to limit the speed of any remaining vehicles to something reasonable. Then the streets belong to pedestrians, as they should.