"In particular I disagree with evaluating the feasibility of potential technology such as L-5 colonies based on comparisons of predictions versus where we are. Nothing happens unless you try to do it and we didn't try. Now I believe we didn't try for the obvious reason it couldn't be cost justified, but that is technology dependent and we certainly have proven we can't predict revolutionary technology very well. Running out of oil is going to be a big motivator for developing new technology eventually as long as we look ahead and don't let our civilization get in an energy starvation mode."

The premise of book is: "The distant future will be very much constrained by what is physically possible and what is not"

I don't think they have a clue of what is or is not physically possible.
Humans traveling into space and living in space is certainly physically possible- the only question is in the political and economic sphere [which one could argue about].

As for the issue of shortage of oil. 200 years ago, there wasn't much need of crude oil- 200 yeas ago the existence or lack of existence of crude oil was not related our survival. Crude oil only became important to humans when the technology was developed that used this energy source.
The issue has nothing to do with crude oil, it has to do with people wanting the "lights on" and cheap energy in general. Cheap energy allows less physical labor- replacing animal energy [horses] with mechanical energy [cars]. Allowing one to use dynamite, instead of humans with mining picks. Etc.

Instead of imposing a some stupid arbitrary such as people should not travel from NYC to London for whatever reasons, the question should be how to reduce the total manhours required for a person to travel from NYC to London- and accurately count this manhour cost. And since labor is always a major cost in doing anything- this is what a business generally does.

Now, there is a reason why one should not use America as a model for future energy needs. America is under populated and more relevant it generally has low population density.

If you think energy efficiency is important, the obvious route is to find ways to significantly increase population densities- and solving problems related to inefficiencies associated high population densities.
Not that I'm promoting the idea, but simply as example one could provide tax credits for buildings using more underground area. Or simply think more in terms 3 dimensional instead of 2 dimensional.
And course making cities more habitable in general and at a lower cost is a good way to get more people living in them.