While here in the United States we wrangle endlessly about the relative merits of expanding public transportation, or expanding road capacity for cars, in China they are preparing to build a test system that accomodates both, using the same arterial footprint:
Proposed by Shenzhen Hashi Future Parking Equipment Co., Ltd, the model looks like a subway or light-rail train bestriding the road. It is 4-4.5 m high with two levels: passengers board on the upper level while other vehicles lower than 2 m can go through under.Many commenters have ridiculed the concept as impractical because (1) it's too tall to fit under bridges and overpasses, (2) the load on the support struts is too great, (3) it can't turn wtithout hitting cars, (4) cars can't turn without hitting it, (5) drivers will panic, (6) vehicle exhaust will overwhelm passengers, (7) it's terrorist bait, (8) it's too expensive, (9) if it collapsed it would crush everything under it, (10) etc. etc. What a bunch of small-minded whiners. Really, exhaust?
The idea doesn't require exotic and untested technology. Many kindsof equipment, not just trains/trolleys, have been built and used for years that run on tracks. Consider the massive cranes that unload cargo ships in ports, or the equipment that moves material in a steelworks.
It does introduce issues in defining right-of-way between it and conventional vehicles underneath, but here too it's been done before. Look at the VTA that runs between Mountain View and San Jose in California: while the VTA has it's own right-of-way it nonetheless has a separate set of signals that regulates intersections and turning, minimizing the potential for collisions. The straddling bus could be organized similarly, especially on wider boulevards that are more limited access, i.e. without driveways or other frequent turns.
The advantages are obvious: avoiding the need to find dedicated right-of-way, especially in already congested urban areas, or the greater expense of building an elevated track or monorail, or the even more enormous expense of tunneling. Here in Seattle we've had experience with transit tunnels and elevated tracks, their expense, and the public contentiousness, so this is an appealing alternative. And now we're rehashing all the same arguments and confrontations over the light rail extension in Bellevue.
Looking at the picture, however, I can't see how they'll fit anything like 1200-1400 people in one bus unless the production version is much larger.
Construction of a test system of 186km in Beijing's Mentougou district is slated to commence before the end of this year.
Video demonstrating and explaining the concept (transcript here):
Update: resized video to fit better