I want to conduct service area analysis with a roadway network to create travel time contour map. The roadway netwotk is a linear shapefile which stores travel direction (N/S/W/E) and travel time for each roadway segments. So for a two-way road, there will be two lines with opposite travel direction and different travel time. So different lines would be used in calculating travel time from and towards the facility.
However, I don't know how to setup travel direction when creating the network dataset by using the existing travel direction.
Maybe I can set the travel direction of all lines as one-way and let GIS to determine the travel direction? However, the digitized direction of the lines are not the same with the travel direction.