The bandwidth authorities scan the bandwidth of the directory authorities, and then skip them when aggregating bandwidth for votes: https://gitweb.torproject.org/torflow.git/tree/NetworkScanners/BwAuthority/aggregate.py#n755 It would save directory authority bandwidth to skip them at the scanning stage instead. We could do this by adding 'Authority' to the forbidden flags for entry, middle, and exit nodes here: https://gitweb.torproject.org/pytorctl.git/tree/PathSupport.py#n1151