A nonstop traffic system using a cloverleaf, comprising: - a first roadway providing a go straight; - a second roadway providing a go straight in a direction perpendicular to the first roadway, with a half cloverleaf provided at a cross point where the first roadway and the second roadway cross with each other, wherein said half cloverleaf comprises: i) a half overpass providing a go straight in two directions on the first roadway; ii) a half underground roadway provided below the half overpass and providing a go straight in two directions on the second roadway; iii) a pair of half underground-turn roadways provided below the half overpass and providing a U-turn to the opposite lane of the first roadway before the vehicle goes on the first roadway and enters the second roadway; and iv) a half aboveground cross overpass provided below the half overpass and between the pair of the half underground U-turn roadways and allowing a pedestrian on the second roadway to walk on the opposite lane after crossing the second roadway; characterized in that said first roadway forms half underground U-turn roadways (200S, 200N) at an interval from the half cloverleaf, and said half underground U-turn roadways (200S, 200N) each comprising: l) a half overpass providing a go straight in two directions on the first roadway; m) a half underground U-turn roadway provided below the half overpass and providing a U-turn to the opposite lane of the first road when a vehicle goes on the first roadway; and n) a half underground cross roadway provided below the half overpass and in vicinity of the half underground U-turn roadway and providing a crossing below the half overpass; and wherein said second roadway has half underground U-turn roadways (200E, 200W) at an interval from the half cloverleaf, and said half underground U-turn roadways (200E, 200W) each comprising: u) a half overpass providing a go straight in two directions on the second roadway; v) a half underground U-turn roadway provided below the half overpass and providing a U-turn to the opposite lane of the second road when a vehicle goes on the second roadway; and z) a half underground cross roadway provided below the half overpass and in vicinity of the half underground U-turn roadway and providing a crossing below the half overpass. - a first roadway providing a go straight; - a second roadway providing a go straight in a direction perpendicular to the first roadway, with a half cloverleaf provided at a cross point where the first roadway and the second roadway cross with each other, i) a half overpass providing a go straight in two directions on the first roadway; ii) a half underground roadway provided below the half overpass and providing a go straight in two directions on the second roadway; iii) a pair of half underground-turn roadways provided below the half overpass and providing a U-turn to the opposite lane of the first roadway before the vehicle goes on the first roadway and enters the second roadway; and iv) a half aboveground cross overpass provided below the half overpass and between the pair of the half underground U-turn roadways and allowing a pedestrian on the second roadway to walk on the opposite lane after crossing the second roadway; l) a half overpass providing a go straight in two directions on the first roadway; m) a half underground U-turn roadway provided below the half overpass and providing a U-turn to the opposite lane of the first road when a vehicle goes on the first roadway; and n) a half underground cross roadway provided below the half overpass and in vicinity of the half underground U-turn roadway and providing a crossing below the half overpass; u) a half overpass providing a go straight in two directions on the second roadway; v) a half underground U-turn roadway provided below the half overpass and providing a U-turn to the opposite lane of the second road when a vehicle goes on the second roadway; and z) a half underground cross roadway provided below the half overpass and in vicinity of the half underground U-turn roadway and providing a crossing below the half overpass.