Calculating uphill/downhill areas on a raster map

[MikeTotti]

Hi folks,
I need to determine uphill or downhill areas along a road section on a raster map. I know MapCal program can do this but it only accepts maps in 100x100 pixels but my study area is too big to run this program (1500 x 1500). I was wondering if there is a way to do this in ArcGIS.

Thanks in advance.

-Mike

[MarkBoucher]

I don't quite understand the "triangle" you are talking about.

If you define the watershed for a piont, not on the road, but far downstream so that it includes all of the drainage points that cross the road, then you will have a polygon that covers the entire road. Then slice this polygon with the road and choose the side/sides that is/are uphill of the road.