The velomobile will be the next great technology to reach ubiquity.
(Assuming that everybody behaves in a perfectly rational manner, which is not a safe assumption, unfortunately)
Near the beginning of August the web was abuzz with news that obesity incidence in the US has continued to increase; more recently, it was suggested that obese people visit general practitioners more frequently than smokers and generally unfit folks. Obesity is bad, this is not news--with the distributed costs of public health care, obesity is even worse. Another bit that isn't news is that a moderate, sudden, and sustained escalation of petroleum prices, perhaps as a consequence of finite/dwindling supply, would likely lead to cataclysmic economic destabilization because of our profound reliance upon it--a point practically self evident in the most rudimentary economic perspective. Of course for whatever reason many more people have petroleum centric anxiety manifested as fear of global warming, for which the more dire consequences won't happen until a fair while after we've already run out of gas if we keep increasing our consumption.
But for a culture in which the automobile was supplanted by the velomobile, these problems amongst many others would be made irrelevant.
What is a velomobile? It's a pedalcar, resembling a grown-up soapbox racer with bicycle pedals. This is a velomobile:
The typical modern velomobile is little more than tricycle recumbent with a fairing, but these two things together make for something of an advanced vehicle. Here's what it looks like in the cockpit of a good DIY velomobile that was constructed for under $1500 (full flickr here):
Recumbents are increasingly popular as they can provide more comfort than the usual bicycle and also utilize the mechanical advantage from having lower back support while pedaling. The fairing adds the benefit of aerodynamics, a good thing as air is the principle force that slows a cyclist. But the fairing does more than that: by enclosing the tricycle, it is suddenly a vehicle equipped to ride in inclement weather; perhaps even more important, what was a bike now strikes the casual bystander as a car. Unfortunately the fairing adds weight... and with intuition it becomes clear that with the minor addition of a small electric motor, this vehicle is the most sensible form of transportation ever devised.
On flat terrain with no wind, an average person can sustain 25 MPH in a velomobile without much difficulty. With an electric motor I'd expect one would be able to sustain 25 MPH while going up a decent hill.
There are many exciting things about velomobiles--by my figuring they potentially represent the cheapest, safest, cleanest, healthiest, and most sustainable form of transportation ever conceived--but the most exciting thing about it all is that like bicycles there's already an international legal precedent for their use on public infrastructure. In the US a velomobile is classified as a moped, as long as it has pedals and doesn't exceed 20 MPH (varies by state). Because of this a velomobile can be piloted on public roads with all the rights of a cyclist, which tend to be more generous than the rights of motorists, no registration or insurance necessary. Newer velomobile designs incorporate headlamps, turn signals, and brake lights; with an electric motor you could drive with city traffic as though you were one of the internal combustion monstrosities. The biggest problem with velomobiles is that they haven't caught on yet, and as part of that, nobody has been able to produce one on a large scale for a price within reason.
This is an incredible custom velomobile, replete with water-filled airbag suspension (full flickr here):
This velomobile is somewhat commercially available, total price >$6000 (retail site here, worklog here):
With the widespread adoption of velomobiles our country could reap the benefits of increased general health with vastly reduced vehicle related expenditure, and thus an increase in overall prosperity. Perhaps even more important, we'd reduce our exposure to calamity by decreasing our extreme dependence on a steady (and foreign) supply of petroleum at a steady (and low, and further subsidized) price. Not that I think adoption should be limited to US.