title: VISSIM COM Interface VehicleNetworkPerformanceMeasurement
body: <p>I'm using Python to communicate with the VISSIM traffic simulation software using its COM interface.  </p>
  
  <p>I'm trying to access the VehicleNetworkPerformanceMeasurement total delay attribute while running a simulation</p>
  
  <pre><code>#run vissim
  env = win32com.client.Dispatch('Vissim.Vissim.800') 
  
  #load layout,network
  env.LoadNet( r'X:\Users\rHalabi\singleIntersection\Ryan.inpx')
  env.LoadLayout( r'X:\Users\rHalabi\singleIntersection\Ryan.layx' )
  
  #tell vissim to collect vehicle performance data
  env.Net.Evaluation.SetAttValue( 'VehNetPerfCollectData', 1)
  
  #run a few steps
  for i in range(10):
      env.Simulation.RunSingleStep()
  
  #collect results
  env.Net.VehicleNetworkPerformanceMeasurement.AttValue( 'DelayTot' )
  </code></pre>
  
  <p>The last line returns an error</p>
  
  <pre><code>com_error: (-2147352567, 'Exception occurred.', (0, 'VISSIM.Vissim.800', 'Sub-attribute not specified', None, 0, -2147352567), None)
  </code></pre>
  
  <p>I've tried other attributes besides 'DelayTot' but none work.  I've followed the documentation and been able to query other objects no problem.</p>
  
  <p>How do I access this data?</p>