For clarification, when I say traffic, I am referring to all types of traffic, not just automobile. Automobiles already have the ability to use alleys and side streets, and do so frequently to avoid congestion on main roads. My concern is that if the city further reduces automobile capacity on main roads, there will be more congestion, and more and more automobiles and trucks will use side streets and alleys instead. I think we both agree that would be a negative consequence. So maybe the city should instead try and redirect bike and foot traffic off of main roads, and onto side streets and alleys. That is what I was trying to get at in my original contribution, but it's difficult in 140 characters.
And in response to your concern about automobiles "taking over", they are already the predominant mode of transportation in Pittsburgh, and that will only become more pronounced as self-driving and fuel-saving technologies advance. Building a better transportation infrastructure in Pittsburgh will depend on accommodating for what people will do instead of deciding what we think they should do.