I've generated a Python script that determines the service areas for either schools (points) or informal settlements (polygons) based Toblers Hiking Function from the article published by Kaitlin Yanchar using Path Distance Analysis. The input cost raster to the Path Distance tool is the slope grid that is used in combination with the elevation grid and the vertical factor table based on Toblers Hiking Function. I would like to include the road network as part of the cost raster, but not sure how to proceed. The input cost raster has to be the slope grid and cant be a weighted cost raster as one would if you combined multiple criteria such as slope, road networks, landuse etc as the vertical factor is used to determine the time is would take to traverse the terrain based on the slope and elevation grid. Any suggestion in how to incorporate the road network as more preferable than walking over the hillslope will be appreciated.