For greater benefit, the railway freight requires operation of double-decked container trains, making the clearance under the railway overpass insufficient.

From purposes and clearance specifications of reserve runway, this paper points out the deficiencies in the airfield clearance regulations of reserve runway, and presents the composition of and the requirement for the reserve runway clearance area.

By site monitoring,such as ground settlement,clearance convergence,vault crown settlement and site observation, etc.

According to the spatial structure analysis of buildings and OCS,the calculation method and criterion of headroom used for OCS pass of existing railway line are given.

Airport clearance limit and obstacle location serves as a special one to understand and promote the relation between clearance limits and obstacles.

In the process of using the military airfield regulations in clearance,since the user may confuse the current rule with the old one,the paper analyzes and compares the differences between the current rule and the old one in clearance,with special emphasis placed on the revised parts of the basis principles,the composition of the clearance zones and the obstacle limits.