What is the maximum allowable slope or angle when constructing roads?

Question

is there a specifations from highway engineering?

Answer 1

It depends a bit on how long the road is.  Typical max highway grades are 5-10%.  Short stretches of road can be 15% or so.

Answer 2

for streets it depends on what the speed limit is too. ive driven on streets of an angle >>20 degrees but the speed limit was very low.