I think just rigorously enforcing the speed limit (at 55 or 65) would be enough, but we need something symbolic but effective that really doesn't limit the market forces per se.

I think the efficient speed limit idea works on many levels, and while unpopular at first to some, I think people would ultimately respect that this is a valid response short of a tax or shortages.

It certainly beats closing schools, like they did in Georgia.

But I'm open to other suggestions. What yours PDXpat?

Nothing wrong with enforcing the current speed limits.  But 55mph accross Montana would never fly.  The trend in recent years has been to increase speed limits (e.g., now 70mph in several states).

I think the public would be much more receptive to improved fuel efficiency requirements, which are more obviously associated with conservation in people's minds.