Through a series of links, I wound up at a blog advocating mechanically (or electronically, I presume) limiting the maximum speed of passenger vehicles to 55 kilometers/hour (34 m.p.h.). Scott (the blog's publisher) lists the benefits, among others as: elimination of oil imports; reduction of CO2 emissions to below 1970's levels;
reduced loss of life and reduced injuries in motor vehicle accidents; reduced air pollution from exhaust; reduced particulates from tire wear; reduced energy in automobile manufacturing due to smaller and lighter components; reduced expenditure for infrastructure maintenance; increased motivation to use (now comparatively much faster) public transportation; and others.
He addresses many of the objections he anticipates as well, though I doubt that many who contemplate his suggestion will agree that he has adequately done so. He moderates his comments and states that a huge portion of the comments he's received consist only of name calling and doesn't publish them. In fact, there are very few comments published. I left several; time will tell if he publishes them.
And though a few of the comments I posted related to his erroneous use of "exponentially" and his stating that aerodynamic drag (as opposed to power required to overcome it) varies with the cube of speed (rather than the square), my main point of contention was that he makes broad claims (elimination of oil imports, reduction of CO2 emissions to pre-1970's levels) with no data or calculations to support them. This is something I try never to do, as claims without backup are plentiful on the 'tubes. I'm willing to be convinced, but he'll have to convince me.
Further, I am instinctively opposed to mandates and top down controls, so I suggested that the externalities of fast driving be paid for by those doing the driving, probably by a tax. With OBD-II on all modern cars, this could easily be accomplished at registration renewal time without big brother-like GPS tracking. The idea would be that people would be taxed on the extent to which they exceeded, on average, some speed and probably multiplied by the number of miles driven. I can already hear the howling!
But let me do his job and suppose such a thing was done. Would we eliminate oil imports? This needs to be a two part question because we'd use less energy to travel and use less energy to manufacture automobiles. For the first part, I'm going to assume that the adjustment has been made and that enough of the new variety of cars optimized for such a maximum speed are on the road to use them as the de facto standard. In the real world, that will take a while but let's see where it leads us.
We used (in 2005) 320,500,000 gallons of gasoline per day at 17.2 m.p.g. I made liberal (but not completely unrealistic) assumptions on vehicle characteristics of weight, drag coefficient, rolling resistance, and area and calculated in the usual way - details can be provided if requested- and determined that we'd be able to get vehicles achieving about 134 m.p.g. after this rule is implemented and the situation stabilizes as described. At that rate, we'd save about 87.2% of the gasoline we now use, or 279,000,000 gallons per day. Now, we get about 19.5 gallons out of a barrel of oil, so we'd save about 14.3 million barrels per day. This is, in fact, more than we import so Scott is correct. This doesn't even include savings from reduced energy use in manufacturing lighter vehicles. I'll attack that, and CO2, in a subsequent post.