To continue to build roads will continue the problem. The answer is
puvblic transport, but public transport cannot cater for all journeys
and therefore over time journeys will need to become more
corridored.

What exactly do you mean by "more corridored"? Most long distance journeys
are already corridored into the rail and motorway networks.

For example go into any city during the am peak and the tidality
of the flow is there to be seen.

Yes, commuting into city centres is probably the only thing that public
transport *can* cater for.

Without cars on the urban road network public transport would be
faster and more reliable.

Indeed it would. However, the current situation we have is that public
transport routes rarely cater for where you want to go. For example, to do
my route to work I would have to get a bus all the way into the city centre,
then another one out again at a different angle - taking well over an hour,
when my destination is just 7 miles away but in a direction not catered for
by the bus network.

We know that building more roads is
a) environmentally damaging

How so? Surely free flowing traffic is using fuel more efficiently, and thus
polluting less, than a traffic jam with thousands of cars hardly moving at
all?

b) increases usage so essentially provides no longterm greater net
capacity.

Usage does increase, however that usage tends to come off local residential
roads, thus making life far more pleasant for residents.
For example, you could argue that the M60 completion in Manchester filled up
to capacity almost on the day it opened, which may be true - but if you look
at the bigger picture and how much quieter local streets in the area are,
surely it's worth it.

So where do you stop, when the whole country is one great network
of asphalt???

Don't be silly, we're nowhere near that. I don't think the motorway network
even takes up 1% of the land in this country, there's plenty of space for
more.

Look at a map of Germany, and compare it to a map of this country. They have
motorways all over the place, yet they still have plenty of countryside to
enjoy.