The traffic gridlock on Bents Lane and Marple Road has been shocking for as long as I can remember - 30+ years. This is not a new phenomenon and the poor residents of those areas have been suffering for so long they're probably resigned to putting up with it. I have met many people who used to live in Marple through work and the very first thing they always remark on, without exception, is how bad the traffic is. These are people who have to commute by car to different locations, and for whom public transport is rarely an option. It is often the main reason why they left the area.
New roads do improve traffic flow. The evidence / experience of this is obvious. Getting North to Ashton / Oldham / Rochdale / Bury etc is so much easier than before the M60 extension was completed. Journey times have been slashed provided you can get out of Bredbury. It's easy to forget how bad things were before the M60 was finished about 18 years ago. Go to Ashton Moss now for the cinema in the evening and you're looking at a 15 minute trip - it's fantastic. The M6 toll around Birmingham drives like a dream, especially compared to the old alternative. The new road to the airport should be similarly beneficial. It currently takes me an hour to get there in the morning which is patently ridiculous and simply unacceptable.
There will be objectors, there always are, but this road is long overdue.