Hi Para Dige,
It might be a bend where the entire road has a slight angle to maintain the speed which is general in Freeways (highways). Highest mid point is ok with roads operate under ~ 60 km/h which we already have in Sri Lanka. Above that speed the angle of a bend matters the stability of vehicles. That is the reason why the water flow the other way you have expected.
Yes you are correct Eranga,
that is called Super Elevation
, Actually our normal roads with 60km/h speed limits also should design according to this way.
But unfortunately our RDA don't worry about the Correct Elevations of the bends
So we can see totally opposite side angeled bends in our country.
That is very unfit to the vehicles with high speed. ....
Even at 60Km/h....