Calculating road/air/sea capacity?

[Simons Mith]

The wiki gives decent info on how many trains a given network can support. Does anyone have the equivalent numbers for road, air or sea?
So far I have one rule of thumb; using the 8mph 9t-capacity horse carriages, a road has a maximum capacity of about 100t/month. So
presumably with 12 mph 9t-capacity 2-horse carriages, that should go up to about 150t/month. And so on. But that's based on emprical
observation; is the info needed to work out the precise values actually available? Has anyone privy to the figures actually done the
calculations?

Also: same query for ships and aircraft.

[Supercheese]

Ships have infinite capacity, you can always keep adding more ships and they will never have to wait for each other.

[leifbk]

I'm playing a lot with the horse carts. In metric units, I've found that the 2-horse carts can manage about 100 tons per month; that's with reduced breakdowns. The capacity will go way up if you disable breakdowns of course, as it will go down with normal breakdowns.