为解决设计人员对明棚洞建筑限界与路基同宽理解不一致的问题，通过对隧道建筑限界和公路建筑限界的横断面组成进行对比分析，根据规范中关于同宽的功能要求，推理得出： 独立设置的公路明棚洞建筑限界与路基同宽应理解为车行道宽度与两侧侧向宽度之和同宽，同宽标准应采用公路建筑限界（一般值）与隧道建筑限界（车行道+侧向宽度）两者的较大值。由于需要在洞内布设检修道或人行道，独立设置的明棚洞在满足前述同宽要求时建筑限界基本宽度将等于或大于公路路基宽度而导致明棚洞结构超出路基宽度较多的问题。针对该问题，对检修道或人行道的功能进行分析，分析结果表明： 独立设置的明棚洞可考虑将人行道分离设置于结构外侧，从而有效减小明棚洞结构跨度，改善顶梁内力，方便结构基础布置和施工。

In order to solve the problem that the designer′s understanding of the building boundary of the opencut/shed tunnel and the subgrade, comparative analysis of the crosssectional composition of the tunnel building boundary and the highway building boundary are conducted. According to the functional requirements of the same width in the specification, it is inferred that the independently set highway opencut/shed tunnel building boundary and the subgrade width should be understood as the sum of the width of the roadway and the lateral width of the two sides, and the same width standard should adopt the larger values of the highway building boundary (general value) and the tunnel building boundary (lane + lateral width). Due to the need of laying maintenance roads or sidewalks in the tunnel, the basic width of the building boundary of the independent opencut/shed tunnel will be equal to or greater than the width of the highway subgrade when meeting the abovementioned requirements for the same width, resulting in the problem that the structure of the opencut/shed tunnel exceeds the width of the subgrade. To address this problem, the function of the maintenance lanes or sidewalk is analyzed, and the analysis results show that the independent opencut/shed tunnel can set the sidewalk on the outside of the structure, so as to effectively reduce the structural span of the tunnel, improve the internal force of the top beam, and facilitate the layout and construction of the structural foundation.