Considering the size of China it does not surprise me that in some places the infrastructure is a bit outdated and bound to decay in front of you. It´s a luxury to live in Germany, an almost tiny yet relatively wealthy country which is famous for it´s network of highways where cars can travel safely at speeds which are usually illegal in most other countries.
alex251 said:well in other countries they make such things under the road
Well, you should know that one of the main purposes of an aqueduct is to make use of naturally occuring slopes and cross gaps while (mostly) avoiding the usage of pumps. So it is/was only natural to build these bridges above ground.
It should be noted that the US have some of the largest aqueducts of all time.