Construction method of disc-type left-handed overpass

The disc-type left-handed overpass consists of a lower roadway, an upper roadway, a bridge aperture, a viaduct, two turn roadways and a circular roadway. In the overpass, turning left is in a parallel slope, turning right and turning left are convenient and it is favorable to heavy truck to step up from the lower roadway to the upper roadway. The overpass has four layers of roadway in a relatively lower height and thus lower cost, and it has a short turning left path.