There are 3 security areas- for the three gates- C, D, and I think A- 95%- "A" is normally just dead- so if C & D- are backed up - we walk down to A- and go right through- then you and to walk back within the "secure" area to D, C or to the train of N- have found "A" slow with less stress- if you don't mind a little walk. rlb
If the OP is transiting SEA late Sunday evening, be aware that the N / D security checkpoint closes down at a certain hour and everybody has to hike down to the central checkpoint that dumps into the food court, then back up to the N / D gates. This adds unwanted time to your security experience.