I'm currently having a problem determining 'realistic' walkable catchments for a footpath network. Specifically I would like to build service areas for a number of locations that take into account both footpaths (that run on either side of a road network). In other words are you able to set a gap tolerance which would allow the service area to 'jump' midway down a line segment from one footpath to the other and and then say continue down another road.
Network Analyst traverses the network. So as long as you have edges that connect places where you can travel, a path can be found. You could connect a footpath to another footpath, midway, with another edge. Take a look at the Paris network in the NA tutorial on how to add additional edges to connect the road to the metro network. Jay Sandhu