Student or Learner
The snow covered the train tracks by more than a foot, (promting the transit authority to shut down serive and causing discontent among communters who were left stranded for hours.)
could you please tell me what the phrase in the parenthesis called as? what function does it do here?
The short answer to your question is 'It's a subordinate clause', the longer one is 'It's a subordinate clause that uses two present participles to disguise the fact that among all that flim-flam there is an inconvenient duality of subjects '
[ I have two lessons to prepare, so I'm being unusually contentious as I don't have the time to be more tactful. Official 'spin' annoys me. Sorry.]