Platform doors are certainly not common here. Here is the New York Daily News reporter's take:

"Meanwhile, at the Third Ave. stop, the MTA is designing platform doors, which are common in transit systems in Asia and Europe. The closed doors open to allow trains into stations, preventing the cars from hitting people who jump or fall onto the tracks.

“We’re in the design planning stages and working to overcome structural challenges for a small platform screen doors pilot at the Third Ave. station along the L line,” MTA spokesman Jon Weinstein said in a statement.

MTA officials picked the Third Ave. L train stop because it’s straighter than other stations, the platform has five feet of clearance from the edge without any obstructions and it has enough power to operate the train doors without disrupting service."

Now that would be interesting... :)