whunter,
Yes, this a good thread; see what other's thoughts are, etc. I'd repeat what a # have said. Minimizing automobile useage by car pooling, freeing congested downtown areas of larger citie's through shuttle busses, overhead cable suspended "pods" of the type used to move 30 to 50 skiiers at a time. Upgrading railroad tracks (billions and billions of bucks, I know) to allow the use of high-speed passenger trains for long-distance travel (trains running close to 200mph on straight grades; as super-conducting magnets become more efficient, going beyond the prototype MagLev trains that use this technology (no contact between train and I-beam style rail) allowing trains much, much higher speed for longer and even shorter communter style distances). The automobile isn't disappearing anytime soon, but mass-transportation can take so much stress off the transportation system as to be crucial. The use of steel rail/wire in highways, without direct connection to the car, but the car tracks the rail/wire and computers control the cars speed, optimizing traffic flow on high-volume highways, even on sparse sections of Interstate; producing fewer accidents, less fuel used from eliminating excessive stop and go situations. The increased building of nuclear reactors to charge electric cars, also to use nuclear reactor heat to melt the oil shale and tar sands to produce useable dino fuel so as to be cost-efficient. As to cars, themselves: smaller, lighter, stronger, more fuel efficient. The greater use of compressed natural gas powered and fuel cell cars. I think it's going to be a process that moves in noticeable step changes, but I think the large SUV & Pick-Up truck market has seen it's hey-day and won't return to levels seen in the past ten or so years. But, the smaller, lighter replacement vehicles that still run on dino will have engines that produce much more power so that the ratio of horsepower to vehicle weight will be increased.