It seems like we could use bicycles as transportation a lot more than we currently do.
Of course we could, that's self evident. The problem is convincing people to want to.
As an illustration, back in the early '80s during one of the past "gas crises", Yamaha commissions a study to see what part of the population would consider a motorcycle as at least a partial substitute for their car, citing vastly better fuel economy (60 mpg is easy for a moderate size motorcycle and much higher is available with small displacement bikes).
The survey showed well over 80% of respondents wouldn't consider it no matter how expensive gas became.
And this survey was about motorcycles which require almost no physical effort and can keep up with auto traffic easily. What do you think the results would be for a similar survey about bicycles?
Bicycle commuters and those who use them for shopping, errands, etc. fall into two categories; 1) a small number of dedicated riders or 2) those so far down on the financial food-chain that a bicycle is their only choice.