I recon Labour could pull a rabbit out of the hat, if they're infrastructure review highlights a need for extra North/South capacity, but says that to build a new road would take 15 years before it was able to start work and another 10 to deliver it. Yet the construction of HS2 to Crewe would give us enough capacity improvements to ensure that the new road wasn't needed for another (say) 25 years, whilst High Speed lines to Manchester and Liverpool this could delay the road for 40 years. Not least due to the extra local and freight services which could be delivered (and actually detail what this could look like), as well as how it would benefit those still using roads (as whilst it might not make the queues shorter than they currently are the added delays over time would be far smaller).
Having determined that, it then goes on to say that having looked at these Western facing high speed lines that the extra to deliver an eastern facing element to create an East/West route could be delivered fairly quickly (still 15 years out, for the whole lot, but would be able to be delivered in stages so as to improve this vital link). Again detaining an example of how this could also improve other services as well as road travel.
To really make people take notice, suggest 3 routes for the new road which would be fairly controversial (for example maybe even suggesting that it would need to bisect some town or be the wrong side of a town to a larger settlement - for example east of Bedford so that those from Milton Keynes would have drive through it to get to this new road).