Firstly I would attempt the most simple option of traffic restrictions through the centre of Warrington, other towns and cities have done it and I believe Warrington has the option. 2 or 3 times a week there is a procession of HGV lorries crossing Warrington town centre to get from Lymm to Omega I presume, I'm not sure where else they would be going given the number.
I believe that an infrastructure plan needs to get formulated to get traffic moving efficiently through the bottle necks, maybe widening the main roads (Knutsford Road and London Road are especially bad) and suitable side roads. There are other roads in other parts of Warrington which would also benefit from this such as Manchester Road.
Maybe looking at replacing the old unreliable swing bridges with wider quicker bridges, I have seen in other countries this making a huge impact over a very small time frame.
I would say there is a need to look at traffic flow when the viaduct is blocked, I would suggest a bypass, which I know sounds ridiculous given we are boxed in by motorways but they do not cope.
I would also look at who is going to live in the houses planned as I don't know many people that actually work in Warrington and look at options of how to get them in and out. We have motorways but if you try to leave at the wrong time I have experienced several miles of tailbacks, Knutsford road to Lymm junction can be backed up all the way to Chester Road in Grappenhall.
Lymm roundabout needs to be reviewed, there is a very strange traffic light system on there that all it seems to do is cause congestion as it is not uniform across the whole junction and just causes grid lock.