You say lots of fruit and veg produced in market gardens near cities. Supposedly 200km is near in your calculations. If you had to cart that food without oil you'd not want to be carting it more than 10-20 miles max.

The thing is that as people keep emphasising on TOD, fossil fuels are not going to just STOP. They'll become more scarce. So there'll still be some transport around.

If oil is $500/bbl then oranges from Barbados in London in winter are not going to be viable. But spuds from Wessex will be. You just have to look at history. While there were villages that got only stuff from their own area, there was the occasional town or city that got things from a great distance away.

For this a lot of organisation was needed. But they did go more than 10-20 miles. It was done in the past, so can be done again.

Now, as I said in those articles, we certainly won't be able to have cities of 10+ million people with scarce fossil fuels. Nor will there be the thousand or so cities of over a million we have today. As fossil fuels become scarce, if we don't put in alternatives then we'll see a deurbanisation. But since the fossil fuels won't just stop one day, this will be gradual rather than catastrophic.

Now I shall give more answer to your maths question. Medieval Britain (~UK) was struggling to feed its much smaller population, even though its land was a lot less degraded back then.

We know a bit more about land and water and resources than we did in the Middle Ages. We can do better than we did then, and certainly better than we're doing now.

That doesn't mean we will do better, just that we can. I'm talking about what's physically possible, and combined with that what seems likely given what's happened in the past.

It does not seem likely that fossil fuel supplies will just STOP one day, but rather that they'll decline in availability, and priorities will be set. People will have a very hard time indeed, but they won't starve and perish in an orgy of violence.