I don't know the area but the grid pattern wide carriageways makes 4bph seem pretty doable.
It's not road capacity that's the issue, it's how unattractive bus travel is and how spread out it is meaning each route is only attractive to small numbers of people. People would go by car if they were paid £2 per bus journey. MK is designed and structured for the car and there is no hope at all of removing it without massive subsidy or bulldozing the lot and starting again. Realistically the best you're going to do is a push to switch to EVs by mass charging provision in CMK and elsewhere, and perhaps something like Uber Pool (recognising that you will only match up two journeys at most - big-bus DRT demonstrably doesn't work) but then again that's little better than private cars.
Then the central bit is flat
Have you ever been to CMK?
Clue: it's very much not flat. That does put people off going there by train when they have to walk a kilometre uphill to get to the nearest point of the shopping centre. The central bus spine is the only way to really make it work, which is how it's been for a long time.
and within 2km of the station at furthest, that's less than 10 minutes on what could be a nice segregated bike lane.
You'd need a lot of hire bikes for that! Hire bikes are not mass transport pretty much by definition - the concept of them is for people doing journeys that *aren't* well served by public transport. You'll note the TfL ones aren't located directly outside stations and there's a good reason why. They're in effect a healthier and cheaper taxi substitute (and indeed that's how I use them here).
MK is otherwise quite well set up for cycling and e-bikes take away the hills - but there is a big bike theft problem - I used to leave my bike at MKC station but definitely wouldn't now! Dutch "bewaakte Fietsenstallingen" - staffed cycle storage - would be a good thing but there's a limit to how many will cycle even with that.
I'm not talking about a day 1 bulldoze. Phases revelopment from station working outwards could mitigate the disruption. Yes it would still be a massive project but the whole concept of new towns is a massive undertaking anyway. At least CMK has existing infrastructure.
Apart from roads it really doesn't. And it's structured wrongly for public transport.
I don't doubt MK will expand, I reckon another 20 years will expand it to 400K. But really it would be better to start again - one thing I'd seriously look at is medium sized ecotowns around each Marston Vale station, though the planned ecotown might kibosh a couple of the stations.
Park and ride could be a could temporary (or permanent) solution as well, so people can still drive from outlying areas then hop on bus for final bit.
MK has had P&R before and nobody used it. It's not a concept that works very well in a car friendly city.
EWR might help with the park and ride bit.
Literally nobody will P&R on a 2tph frequency unless going a long distance. You need a much more frequent service for it to work - I'd say 4 at a bare minimum, ideally 6.
I could see sense in adding a Newton Longville Parkway though Bletchley doesn't lack spaces, but that would be for going to Oxford, not CMK.
