Going overhead

A mass transport system above city streets could be the best option for urban town planners

Published: Saturday 15 March 1997

tomorrow's commuters may not travel to work in cars or underground railways, but in overhead carriages 16 feet above city streets. Called System 21, it differs from the conventional light rail transport system in that the trains travel above an overhead six feet steel beam. Futrex, a transport technology company in Charleston, South Carolina, has already built a us $1.6 million (m) model of this futuristic urban transit system and plans to begin construction of a full-size prototype in the next few months.

The main benefit, according to Futrex, is that the system can be operational for us $20m-$25m a mile. This is a fraction of the price of some urban transit systems that have already been constructed and have cost up to $200m a mile.

Another advantage of the overhead transport system is that, unlike trams, road space is not taken away from cars and lorries. System 21 relies on a single beam, making it much cheaper than conventional rail systems that require two sets of tracks to be laid.

The trains, which will have either two or four cars and a maximum speed of about 100 kmph, could be operated by a driver or controlled by a computer. Each car will be attached to the guideway beam by a pair of steel wheels and travel along a rail in the base of the beam. There will also be a steel outrigger, which will link the top of each car with the top of the beam to hold the car in place and make the ride comfortable. To prevent the carriages being derailed or tipping over, the system uses a suspension unit coupled with safety hooks that bind each vehicle to the beam; they are positioned at the front and end of each carriage. The manufacturer claims the resulting link is so strong that trains could survive hurricane winds blowing at 192 kmph.

The system will also allow for overhead switching. This will make it easier to create a number of feeder lines, which could be used to link in with the existing urban transit systems. In fact, trains will be able to turn in a radius of just 90 feet, which means guideways could make right-angled turns above big road intersections and thus follow the line of existing city streets.

A further benefit is that as each system can be built away from its route and then fixed into place very quickly, it will cause minimal disruption to local communities. Besides, the simple construction technique means a route could be expanded easily and stations added at a small cost. The narrow overhead beam means there is also a lot less visual intrusion than with many existing overhead rail systems. Stations would be alongside the beam, with automatic doors opening when a train arrives and elevators and escalators taking passengers down to street level.

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