1) The worst congestion in the Southside is not there, and not due to the shopping complex.
The main congestion that occur are during rush hour around the bridge exits, between the Hot Metal Bridge and Beck's Run Road, and between the 10th Street Bridge and the West End Bridge. These are because, well, people like to leave town and go home after work ends. Funny that.
The secondary congestion that occurs is between 1:30am and 2am between 14th and the Birmingham Bridge. This is because the drunks are leaving the bars and start driving home. Again, this has nothing to do with the Southside Works.
2) The Southside Works is attracting a lot of people to it now, but for how long? Given the lifespans of shopping complexes, and how they're often considerably hurt by localised construction (evidence what has happened with the Waterfront with the Homestead Bridge under construction), by the time this project is done, it's likely that the traffic flow to/from the shopping complex will be considerably less.
3) The main traffic for the Southside Works isn't even on East Carson. Most of the people who shop at that complex, in fact, seem to think that going as far as East Carson to park is a horribly dangerous thing to do, and like to drive right down the middle of the complex looking for a place to park.
Really, if they actually wanted to relieve traffic congestion in the area, they should be widening East Carson on that long stretch between 33rd and the Glenwood Bridge. But, that's probably nigh impossible with costs and tracks in the way.
So, yah, they'll be interrupting my daily business for construction of the street near where I live for a totally futile reason. Thanks guys. Another example of the brilliance that Pittsburgh puts into its traffic engineering.