The 3D Express Coach (straddling bus, straddle bus, or tunnel bus) was a proposed new bus designed by Shenzhen Hashi Future Parking Equipment Company back in 2010. It was recognized by Time magazine as the innovation of the year in 2010.
A proposed trial project was to cost about 500 million yuan (~US$74.5 million) to build the bus with a 40 km (25 mi) guideway. This is claimed to be at 10% of the cost of building an equivalent subway, and is estimated to reduce traffic congestion by 20–30%. The Chairman of the company has said that it would only take a year for one to be built. 115 mi (185 km) of track was set for construction in the Mentougou District of Beijing for late 2010. The cities of Shijiazhuang, in Hebei Province, and Wuhu, in Anhui Province, were applying for financing.
I have not heard of an actual implementation, but there is a new video with refinements to the engineering. The video is by China TBS limited (which is a large shipping company).