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The premise of the TEB is simple. It's a guided bus (i.e. it sticks to a predefined route) that is 4.8 metres high, 22 metres long, and 7.8 metres wide, with ground clearance of about 2.2 metres. Any vehicle that is short enough to pass under the TEB is free to do so, in theory significantly reducing congestion.

The TEB itself is powered by electricity and carries about 300 people at speeds of up to 60km/h (37mph). Larger articulated models that can carry up to 1,200 passengers are under discussion. In China, where congestion is a major issue in large cities, the TEB is being pitched as a cheaper alternative to building subways—the initial 2010 report said that a 25-mile (40km) TEB track would cost a tenth of the equivalent subway.

In practice, though, the TEB is rather complex. Vehicles that are taller than 2.2m would have to take another route around the bus. TEB designer Song Youzhou says that the bus can turn corners—but for any cars that find themselves underneath, they must wait for the TEB to complete its turning manoeuvre before they take the corner, which sounds like a pretty harrowing experience.

There would be an alarm of some kind to warn other vehicles as they approach the TEB, and perhaps some kind of auto-collision-detection that prevents the TEB from driving into over-tall vehicles. It isn't clear if these measures have been included on the full-size model shown off on Tuesday.

Another problem would be vehicles driving into the "legs" of the bus, and then presumably an almighty crash as the cabin loses support and keels over. Song says that this risk would be mitigated with guardrails between the roadway and the bus tracks that can absorb 70 percent of a collision's impact. Looking at the photos of the first installation in Qinhuangdao, though, you can see no such protection.

The passenger experience is apparently like riding on the top floor of a double-decker bus. In a full-scale implementation, passengers would board and alight from elevated platforms by the side of the road, similar to an elevated railway, but for now it looks like they use a stepladder. Apparently the TEB will even have evacuation slides, similar to an airplane.

As far as we can tell, the TEB in Qinhuangdao is simply running back and forth on a short, straight stretch of road. Still, it's an exciting concept. In countries with very specific infrastructure setups—or the wherewithal to make dramatic infrastructure changes to accommodate elevated buses—the TEB could revolutionise public transport.