>>4061805in this picture you have frame of reference for what is actual plumb(the house in the middle) as well as exaggerated steepness because you see the street go down, as well as go up. So this picture is cheating a bit.
For pictures where you don't have such a nice scene, compressing the buildings by using a long focal length and shooting from afar might do the trick. Pic related is a good example, if you shot it with a wide angle from the spot where the street starts to go up, it wouldn't look so steep.
