My old neighbourhood in Toronto, "Davisville Village", is made up of tons of 30 storey commie blocks and ironically it's loads quieter than where I live in Halifax (Oxford Street) for two reasons:
1) Everyone in Davisville takes the subway, made viable by the highrises, or walks
2) Oxford is clogged daily with drivers heading out to low-density suburbia
I would be willing to bet that even Davisville Avenue had less traffic than Oxford. Obviously a neighbourhood of such density as Davisville isn't for everyone but this St John project would be totally appropriate for this area. More of it and the urban form would begin to resemble Vancouver's West End I think.