The Tubenet Transit System

Tubenet Transit CityIn a recent presentation at the Podcar City 8 conference in Arlandal, Sweden, a new Chinese company called Tubenet Transit described their new PRT system, and how it could be used to accelerate eco-restoration and urban reforestation.  As the name suggests, the pods run inside of a tube with guide rails above the pod, and a support surface below.  The top of the tube is covered in solar panels.  The bubble-shaped pod is only two meters long, with an empty weigh of 150 kg (330 pounds), and a carrying capacity of 250 kg (550 pounds), seating two adults and one child.  (Remember China’s “One Child Policy”?)  They described three tiers of guideways, supporting speeds of 40, 60, and 80 km/h (25, 37, and 50 mph).

They are planning for pods to pass by as often as every 0.2 seconds at 80 km/h.  This spacing, known as headway, is much shorter than anyone has attempted so far.  (Existing system have been certified for headways of as little as 3 seconds.)  That extremely short headway allows for impressive capacity, up to 34,782 passengers per hour on a single guideway, assuming every seat is filled.  In the unlikely event of a crash, the air in the tube between pods serves as a safety cushion.  They are trying to get fairs down to 40¢ per passenger-mile, which they claim requires a population density of 6,000 people per square mile.  They noted that the density of the “built-up areas” of Beijing is over 60,000 people per square mile, or 23,487 per square kilometer.  (The average density of Beijing is 3,300 per square mile, or 1,300 per square kilometer.)  They estimate capital costs at $12m per mile of guideway, with a return on Investment in 5.4 years.  Their projections indicate that within ten years, the investment would be returning 10%.

The most unusual aspect of this design is that the pods run inside of the guideway.  That raises some interesting possibilities.  For example, the guideway can provide some protection to the pods from tree limbs, gusty winds, or sabotage.  It provides a good place to locate solar panels, without the need for cantilevered supports.  And it could be designed as a large-diameter truss that could allow for particularly long spans between supports.  In Tubenet, the power rails are located in the bottom of the guideway, but they could be located above, where they would be less of a safety hazard during maintenance or an emergency evacuation.  The support wheels on the bottom of the pod do not need to stabilize the vehicle because that function can be provided by the switch rails at the top.  That means there could be as few as two wheels on the bottom, allowing the pod to be simpler and lighter.  (Although this would require a different emergency escape mechanism.)

There are several new PRT designs under development around the world, but this one is particularly interesting for two reasons.  First because it’s from China, which is undoubtedly the most rapidly urbanizing country in the world.  Whole new mega-cities are being built there, but so far that have all been car-oriented.  Second, because they are promoting PRT as more than just a supplement to existing transit systems, but as the key to a whole new way to design cities that reconnect people with nature.

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