This is closer to an 'infrastructure' level problem than something usable by singular individuals or small communities.. yet there are situations where if it could be made cheaply enough it would be worth doing, for instance if the cost per mile of rail could be gotten low enough and the per vehicle costs low enough this might be usable in a number of areas.

http://en.wikipedia.org/wiki/Personal_rapid_transit

PRT is basically door to door rail service for normally 2-6 passengers at a time. It is not "light rail" moving dozens to a hundred, it is not a bus replacement moving dozens, it is not mass scheduled transit only going in specified routes... the rails replace highways, the cars are ridden in by you and you alone (ie your family and packages) making it "personal", the route is figured out in real time, just like packets moving around a computer network go from node to node to node to get where they need to (there is no 2 hour cycles of circular bus routes), and the get on/get off locations are darn near a replacement for the car as you reasonably can get. Often designed for like a 1/4 mile grid so that a station is never more than about 5 minutes walk, and going straight to your door is possible.

Rail itself has many advantages over roads:
- Greater safety potential, properly designed they dont generally go off the rails, there is no losing attention and steering into oncoming traffic, light posts, and such.
- The cars can move themself, be used by the blind, by children, the injured/disabled, the elderly or maybe just the intoxicated. You can literally have RFID tags and for instance just say "take me home" and it will know where "home" is. Autopilot doens't have to be required, it is just one option, and so is a more credible remote control ability since you don't have to steer, just watch for things on the rail line that shouldn't be there (and wont be if raised rail, or protected by fences and such) and hit the brakes if needed if you see something unexpected.
- Far less land is taken up, a rail can be very narrow. The simple loss of farmland to roads for instance in many of the fertile areas of the world is massive... rails either take very little space, or no space if they are elevated above walkway level. (this also creates safety benefits/children unlikely to be crossing if the walkway is up in the air for instance, animals unlikely to be hit by moving cars as well)
- The infrastructure costs to maintain roads - clear the snow, patch the holes, periodically lay down new tar.. is massively higher and takes far longer than it does to repair or replace sections of rail. Furthermore things like automated clearing of snow and such become alot more credible... or even unnecessary. A narrow rail doesnt gather much snow or can be designed to shed it, on a road it just piles up. A raised rail probably doesn't even need cleaning normally.
- With the right design, far faster braking is possible from a safety standpoint than the contact patch of car tires onto pavement is capable of.
- The cars can generally be alot cheaper since they are alot simpler. Electric power is possible and often a wise use, lighter weights are possible. Different cars can be used for 'high speed' intercity as opposed to around town rural if necessary as can strategies such as having cars interlink back to back making one buslike single aerodynamic profile reducing energy needs to punch through the air at higher speeds substantially.
- Coordination by computer of traffic can be far more efficient than our current system of stoplights and gridlock and rush hour... far higher volumes of cars passed through a section of rail is possible, no idling at stoplights for 5 minutes is necessary, rather 'packets' can move more fluidly and adjust speeds as necessary. Even miniature over/underpasses are possible far more easily than a road, raising the rail is not that difficult, and by some designs may not even be needed. (simple interlocking rail in an X, with the computer letting one car through at a time with high coordination.. yes a computer mistake could cause them to crash, which is why people may not feel safe giving over to that entirely right away without lots and lots of testing, but if nothing else such intersections could be used for freight where there is less concern about such mistakes.)

PRT has both the problems and benefits of 'network effects'... it's like facebook where the only reason you want to be on there is because all your other friends are on there. If they werent you wouldn't be on there. PRT becomes alot more useful when it can actually replace a car, taking you where you want to go, in the same or less time, at the same or less cost, than it would take to drive, at which point going by road starts to seem quaint or obsolete. When enough people are on the grid, more people want to get onto that grid so they too can have door to door service.

Getting the cost per mile of rail as low as possible is one critical barrier I see, since we are talking about impoverished communities trying to take control of their own destinies. The typical costs of roads are in the millions to tens of millions of dollars PER MILE, the costs i'm aiming for is closer to the thousands, not including the cost of labor. It may be possible that compressed earth blocks, or perhaps stabilized earth blocks, along with some kind of 'wear strip' of metal, concrete, or the like could be used... extremely low cost natural building solutions should be looked at and explored and tested as much as possible. It should literally come down to rural areas simply deciding, yeah, we want to be connected door to door so lets just do it... given a CEB machine or two and a couple of people working they can just start building their own rail line to connect to the larger network. (which may use rail designs which are for much higher traffic, better wearing and such, but still far lower in cost than traditional construction methods in the millions)

It could also be possible that the open source car design be built so that it can accomodate roads OR rail...


One big sticking