How to read tunnel drawings

The design line and center line of expressway tunnel do not have the same meaning, and generally do not coincide. The tunnel centerline passes through the center of the arc of the tunnel arch, and the road centerline is the centerline of the sidewalk slab in the tunnel. Because the lateral width of the left and right sides in the tunnel is different, there will be a certain distance.

Looking at the drawings, there should be an upward line and a downward line, with an upward direction and a downward direction; Still look at the mileage, the direction is from small mileage to large mileage.