How can China build a bridge 26 miles long for just a bit over a billion dollars?

How can China build a bridge 26 miles long for a bit over a billion dollars and it 1 billion billion dollars to put in 5 miles of car pool lane in US? And also it takes US much longer to build the 5 mile lane, then it does for chinese to make 26 mile bridge. Road project in US takes several months, years or possibly several years too. They work as snail. Why?