Busy: certainly. Congestion: sure, its that bad now. Gridlocked: that's a level or two above what we have.On the contrary, Cambridge-A1 counts are low because it's absolutely gridlocked every peak
The Design Manual for Roads and Bridges has the figure for a road of this nature to be congested to be 22,000 - which is the same as the 2017 traffic flow between St Neots and Caxton Gibbet. The road is congested. But the new A14 is going to have design year (15 years after opening) values that overtop the DMRB congestion figures for that standard of road by some way (and opening year traffic that nearly reaches those figures), so clearly they are not set where the road is atrocious - looking it's what the USA considers "LOS D" (level of service, with A basically empty) on a system that goes up to F.
Highways England reckon that if they don't bypass it with their new dual carriageway, it would have another 5000 vehicles a day by 2038 - an extra 22% on 2017. That wouldn't be possible with gridlock now.
The A31 near Wimborne sees around 30k on a similar single carriageway trunk road - though that does gridlock on summer Saturdays. The 27k figure for an unupgraded A428 in 2038 is below that. Latent demand on the road is sated by the road.
That's not latent demand. Latent is existing, but not manifest. That is induced demand - brought about by infrastructure improvements. These developments are being approved on the assumption that road and railway will be built.There is huge latent demand for some sort of alternative, given that the council are approving lots of employment development in Cambridge and housing everywhere else.
They want to develop the arc - and the railway is a key plank in that development. But, the railway, on the current traffic demand projected ahead can't really justify being more than the non-London lines interurban lines in East Anglia are - diesel, not overly frequent or fast, and run by short trains. My point is that E-W Rail (in the form it wants to take, and more so in the form we're discussing it taking: electric, etc) needs the development as there's not enough demand without it.