Here on earth hydrogen isn't a naturally-occurring fuel. It's a very volatile element which instantly combines with other elements. It's simply an energy storage medium which uses about 3 times the energy to produce it as is returned when using it in a fuel cell ( and I'm not counting the energy used to transport it or store it, either ). Moreover, the issues with fuel cells aren't anywhere close to being solved despite 50 years of R&D. We still haven't figured out how to keep them working in low temperatures, for example, or how to make them without exotic, expensive materials. In short, hydrogen is an expensive, inefficient battery. The idea of using explosive hydrogen in motor vehicles makes zero sense when storage batteries are on a steep improvement curve. Right now batteries can give a range of up to 300 miles and recharge times as short as 5 minutes with a suitable charger. Moreover, the fuel distribution network ( i.e. the electric grid ) already exists. Given this, exactly what are the advantages of hydrogen fuel cells? You'll need an expensive new infrastructure. Hydrogen is expected at best to be equivalent to $5 per gallon gasoline in terms of cost ( compared to 1/10th that or less for pure electric vehicles ). The only reason hydrogen fuel cells were pushed was to keep the big players in control once the oil ran low. They would simply go from selling you gasoline to selling you hydrogen. In terms of operating cost, simplicity, and longevity, battery-electric vehicles win hands down over anything else. You can even design in recharging on the fly along Interstate highways if need be, although truthfully 99% of trips fall within the range possible with today's batteries. Supercapacitors will eventually replace today's lithium cells, offering even greater range, longer battery life, and faster recharge times. So in light of all this, what exactly is the point of continuing with fuel cells? About the only application where they make some sense is grid energy storage, where perhaps solar power makes hydrogen which in turn is used during periods of no sunlight. For vehicles hydrogen is too dangerous, expensive, and complex. Fuel-cell vehicles still require a small storage battery because the fuel cell can't deliver the surges of power needed for quick acceleration. Might as well just ditch the fuel cell and put in a large battery. Honda and some other automakers have fuel-cell demos only because governments continue to fund the hydrogen-highway boondoggle.
Regarding this whole transit concept, it's interesting but no way does it have the capacity or speed of a dedicated rail transit line. It's basically a quick way to put in something until funding comes in for real rail transit. I also question the safety unless you make it high enough for even trucks to pass underneath. In short, nice idea for some limited circumstances, such as perhaps offering transit along an Interstate highway. For crowded cities like NY, only subways really make sense given their speed, safety, capacity, freedom from weather. Lately transit planners have been coming up with all sorts of schemes like this or BRT to save a buck. Nice, except in the end the money saved comes at a steep price. Maybe this can ( barely ) match a local subway in terms of average speed but not in capacity. And it won't touch express subway ( 25-35 mph ) or electrified commuter rail ( 30 to 60 mph ) in either average speed or capacity. And because it's not physically separated from road traffic you have the same safety issues as a bus or car. What really gets people out of their cars is mass transit which is as fast or faster than driving. BRT has had mixed results because it's rarely as fast as driving. Subways and commuter rail however generally do much better. In the end, it's simple-build cheap and get fewer riders. Cost per rider may well stay the same whether you build this or a subway. I'd rather build a real subway, and massively reduce the number of vehicles on the road. The lower traffic in turn gets some of those for whom the subway isn't feasible onto bicycles.