They're invisible track; you can find it in the track menu. Your supposed to connect the existing track to those red bits of track (they'll change to whatever you connect to it). Then when you place the signals, place them on that short section of track & they'll be aligned properly to the gantry. If you don't do it this way you run the risk of accidently placing the signal onto those unconnected invisible track bits & then the signals won't work.
peter
