Automatically save the db after each run.  Automatically restart the next simulation after one is run while increasing the driving isochrone size.  Add a boolean to check to see if a subnet is active.  This allows for the simulation to be sped up without chaning the behavior.  i.e. passengers will still be dumped of onto other subnets if those subnets are better, but those trips will not be simulated.  This allows for a single subnet to be isolated and tested.