作为轨道交通系统的一个分支，空轨的研究及应用已有超过100多年的历史，目前主要应用于地势相对平坦的地区。为扩大空轨的适用范围，在山地环境等特定地区，将隧道与空轨结构相结合，以缩短线路长度、优化设计、降低造价。从结构受力、结构材料、施工及运营维护等方面对隧道内4种结构形式空轨的优缺点进行定性比选分析。对于隧道内梁柱结构形式空轨，隧道与空轨梁柱结构为2个相对独立的系统，对隧道衬砌结构无特殊要求，受力明确，施工技术成熟，可进行工厂化生产及装配式施工。因此建议优先采用隧道内梁柱结构形式。

As a branch of rail transit system, the sky train has a research and application history of more than 100 years, which is mainly used in flat areas. In order to expand the applicable scope of the sky train, and reduce route length, optimization design and construction cost, the sky train is combined with tunnel in mountainous areas. And then the advantages and disadvantages of several structure forms in tunnel are qualitatively compared and analyzed from the aspects of structural stress, structural materials, construction and operation maintenance. When adopting the form of beam and column structure in the tunnel, the tunnel and the beamcolumn structure are two relatively independent systems, which does not need special requirements for the tunnel lining structure, and is with clear stress condition and mature technology, thus the factory production and prefabricated construction can be carried out. It is suggested that the structure form of tunnel beam and column should be preferred.