of attack. here is mary snow. >> reporter: under ground at new york times square or penn city, cameras are now watching you. police may be as well. >> this is a coordination of in lower manhattan where we bring in thousands, literally, of video feeds. >> reporter: this is where we met up with new york city police commissioner, the goal to prevent terrorist crime. they monitor the surveillance cameras 24/7. 500 cameras have been added. the subway system has 5 million riders a day. terrorist attacks are focused on transportation systems. it's something, given the size and scope of the transit network we have here, we have to make it high priority. >> reporter: it has the nypd learning lessons from london where mayor bloomberg inspected