The invention erects a t-shaped small-span bridge over the original roads at a t-shaped intersection, where the head room between the bridge and original roads is about 2.5 m high for allowing pedestrians and non-motor vehicles to pass through. On the surface of the t-shaped bridge, close to the right inside of the t-shaped intersection, a U-shaped ring road is separately built, which rises from entry to the right end of the t- shaped small-span bridge, turns left and spans the original crossing, then turns round and descends until it joins the surface of a second roadway bridge transversely opposite to the t-shaped small-span bridge; on the surface of the t-shaped bridge, close to the left inside of the t-shaped bridge, the other U-shaped ring road is separately built, which rises from exit end to the left end of the t-shaped small-span bridge, turns right and spans the original crossing, then turns round and descends until it joins the surface of an outside bridge transversely opposite to the t-shaped small-span bridge; and the head room between each U-shaped ring road and the ground is about 5 m high for allowing motor vehicles to pass through. Thus the invention achieves a beneficial effect of low bridge surface and all intercommunication.