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skyTran is a Personal Rapid Transit system concept first proposed by inventor Douglas Malewicki in 1990, and under development by Unimodal Inc. Lightweight two-passenger vehicles suspended from elevated passive magnetic levitation tracks are expected to achieve the equivalent of over 200 miles per US gallon (240 mpg‑imp; 1.2 L/100 km) fuel economy at 100 miles per hour (160 km/h) or faster. A prototype of the skyTran vehicle and a section of track have been constructed. The early magnetic levitation system, Inductrack, now abandoned by skytran, has been tested by General Atomics with a full-scale model. UniModal Inc. is now collaborating with NASA to test and develop skyTran. A skyTran system is being built in Israel as a pilot project. It was initially projected to be completed in Tel Aviv by the end of 2015. As of January 2016 work is ongoing with the test demonstration track. Additional projects have been proposed and/or are planned in France, Germany, India, Indonesia, Malaysia, Saudi Arabia, Slovenia, the United Kingdom, and the United States.
To minimize maintenance and make switching on and off the tracks efficient at high speeds, early versions of the system proposed using the Inductrack passive magnetic levitation system instead of wheels. Passive maglev requires no external power to levitate vehicles. Rather, the magnetic repulsion is produced by the movement of the vehicle over shorted wire coils in the track. The cars would be driven by a Linear motor in the track or vehicle. Therefore, the system will have very few moving parts; primarily just the vehicle itself moving along the track, its parking wheels and door, and fans in heating and air conditioning units; so its promoters refer to the system as "solid state".
On this first version, the passive maglev coils are enclosed and supported by a light shell called a guideway that also captures the vehicles mechanically to prevent derailment. Malewicki proposes a 3D grid design that avoids accident-prone intersections by grade separation, with guideways and their exit and entry ramps crossing above or below each other. Tracks will be supported 20 or 30 feet (6 or 9 m) above the ground by standard metal utility poles. They could also be attached to the sides of buildings.
After identifying problems with Inductrack and the cost associated with it, skyTran described an improved design during a Horizon BBC interview with skyTran at NASA Ames in Mountain View, CA.
New details about the levitation and motor were described in a keynote speech in June 2016, showing levitation stator being plain aluminium plates and motor stator an aluminium tube. The guideway is also significantly enlarged and wider than the vehicle, so the switching can be vertical, going through the guideway. Guideway shape is shown at 16:26 in above referenced video. This new concept can be seen in a short simulation film. Instead of the purely passive inductrack system, the new mechanism modify lift by mechanically angling the magnetic pads and need a servo controlled actuation. The lift control also do the switching by moving vertically through the rails.
Comparison with other public transit systems
According to the US National Transit Database (record of every public transit system in the US), the average light rail system costs $5.66 per passenger ($1.78 for capital cost and $3.55 for operating cost). Light rail projects have cost $100 million per mile ($62,000,000/km) while skyTran would cost only $10 million per mile ($6,200,000/km). skytran infrastructure reduces the weight of empty vehicles to under 70 lb/ft (104 kg/m), compared with light rail vehicles weighing 990 lb/ft (1,473 kg/m).
Maximum capacity of the system is 11,500 passengers per hour per direction is reached by spacing vehicles at 1/2 second spacing. At 80 miles per hour (130 km/h), vehicles would be spaced at 59 feet (18 m) and stopped by multiple redundant safety systems. By automating control of the system, skyTran would be made safer than driving by eliminating human error (> 95% cause of human traffic fatalities). As lines reach capacity, a new line would be built parallel to the first 0.5 to one mile away to provide better coverage of the network.
Malewicki conceived the basic idea of skyTran in 1990, filing a US patent application that year that was granted as US Patent #5108052 in 1992. He published several technical papers on skyTran in the following years. In 1991, he presented a paper entitled "People Pods - Miniature Magnetic Levitation Vehicles for Personal Non-Stop Transportation" to the Society of Automotive Engineers (SAE) Future Transportation Conference in Portland, Oregon. The paper is a thorough description of the concept at that point, although some important features of the current skyTran design are only discussed as options, including magnetic levitation rather than wheels and hanging below the guideway instead of riding above it.
The paper describes how Malewicki had built and driven a freeway-legal 154-MPG car in 1981, but realized it could never be safe on a street surrounded by far larger and heavier vehicles. Elevated tracks would allow a very light vehicle to be safe. They are also basic to the system's inexpensiveness, because there is no need to acquire a huge right of way and tear down buildings. It presents an aerodynamic analysis (Malewicki is an aerospace engineer) supporting claims of very high energy efficiency (the paper claims 407 mpg‑US or 489 mpg‑imp or 0.578 L/100 km for skyTran's current two-passenger tandem design, though the Unimodal site claims only, "over 200 mpg‑US or 240 mpg‑imp or 1.2 L/100 km"). It also described how a very light vehicle that can squeeze both surfaces of a track simultaneously could reliably achieve a 6-G deceleration, allowing it to brake safely to a stop from 100 miles per hour (161 km/h) in just 55 feet (16.76 m).
The 2008 energy shortages stimulated renewed interest in Green vehicle proposals such as skyTran. The "Maglev skyTran" topic quoted a number of skyTran and Personal Rapid Transit ideas, such as passengers exiting and boarding at off-line elevated "portal" stops while high-speed traffic continues to speed by on its main line.
In September 2009, the US NASA (National Aeronautics and Space Administration) signed a Space Act joint development agreement with Unimodal. Unimodal has tested prototype vehicles on short guideway sections at NASA's Ames Research Center, in Mountain View, California. NASA control and vehicle dynamics simulation software was made available to Unimodal, which hired NASA subcontractors to program them using US DOT grant funding.
In June 2014, Unimodal and Israel Aerospace Industries (IAI) contracted to build a 400-500 meter elevated loop test track on IAI's campus in central Israel. If the pilot project is successful, IAI will build a commercial skyTran network in the city of Tel Aviv, Herzliya and Netanya. In April 2015, Money transfer for the project in Herzliya was approved, which significantly promotes the project in Israel.
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