I am attempting to limit the travel of most school buses down local streets and other undesired locations without creating barriers. We cannot fully limit travel due to special education buses needing to be able to traverse down the streets should there be student there. I am accomplishing this using network parameters and attributes. I am able to adjust the parameter in the layer properties during a solve at the desktop level. Is there a way during a Python script so that I can make those adjustments and run repeated solves for a fleet or am I stuck doing one at a time and adjusting it manually?
Hello. There is a way to edit parameters using Python, but only in ArcGIS 10.1, which isn't released yet. You can use 10.1 if you're part of the Beta program. I think you can sign up for it at betacommunity.esri.com, if you're interested.
A new 10.1 Network Analyst Python module provides access to solver parameters; for example, here is a link to the help for VehicleRoutingProblemSolverProperties class. However, if you get access to 10.1, you might want to consider using the new restriction model instead. The new restrictions allow you to avoid certain edges rather than prohibit them entirely. For instance, you could choose to mark your local streets and undesireable streets as restricted, then set the Restriction Usage parameter to Avoid: Med or Avoid: High. This would allow buses to travel on those streets, but they would try to avoid them, which is similar to what it sounds like you are doing with your cost attribute parameter. Here is a 10.1 tutorial exercise on the subject.
Last, I don't understand why you need to solve routes repeatedly. Are you using the VRP solver or are you running a custom VRP solution?