A personal interest in spatial analysis lead me to create a road distance map consisting of combining the road layers of Colorado, Interstates, US Highways, State Highways, major roads, local roads, USFS & BLM roads and associating a speed limit to them.  Then converting the vectors to rasters and combining them with a background layer of walking speeds.   Ultimately, it was possible to create a map of the time it took to travel from one point to any other point in the state of Colorado based on speed limits and estimated walking speeds.  The Interstates play an interesting role of being the conduits to high speed travel.