Ever since James Watt invented the steam engine advances in engine and fuel technolgies have led to advances in transportation technology.
The steam engine made the locomotive and railroads possible. The internal combustion engine was the power source that allowed men like the Wright Brothers to take flight, the power source for Henry Ford's Model T, and for Chis Smith's Chris Craft speed boats and pleasure boats. There are new advances on the way, and these will almost certainly lead to new vehicles such as SWATH or HARTH boats, hydrogen fuel cell powered cars, solar electric cars, mag lev trains, and much more in the relatively near future.
Solar power has been a reality for decades, but it has not become the motive force for vehicles because the space (square feet of solar panels) needed to produce enough electricity to move a fairly heavy vehicle is too large at the current efficiency of photovoltaic technology.
Electric cars are viable, and have seen limited use, but the amount of battery storage space needed, and the costs of good batteries have combined to make automobiles that can compete with gasoline powered internal combustion vehicles on the basis of operating efficiency and cost slow in coming.
Hydrogen fuel cells are thought by many to have great promise for the automobile of the future, but problems with the volatility of hydrogen and oxygen in combination seem to have stalled this technology.
Internal combustion engines running on methane or other fuels may soon compete with gasoline, and gas electric hybrids are of course a reality already seeing use on the roads. Hybrid technolgies employing two or more of the technologies mentioned above are very likely. A solar electric car, with a decent battery bank, and electric charging or fueling stations, and a small internal combustion engine for emergency charging is a very buildable and realistic option.
Barring intense economic hardships new technologies are often slow to reach the mainstream, and gas prices may have to rise even more to make some of the other the better option, but many of the possibilities are better for our environment than the cars now on the road, so despite the "pain at the pump" perhaps it is all for the best in the long run.
