Wow! Doing the math (assuming it was three rows per car, not the 4 when it initially opened), 1680/36(riders per train) = 46 2/3 train (rounding up) = 47 trains. 60(minutes per hour)/47=1.27, which means 1 train was dispatched every 1 minute, and 16 seconds!
(Which leads to the question, how did they have enough trains? Train 1 leaves the station, so, it takes 1 minute, 16 seconds for both train 2 and train 3 to leave, train 1 is then only 2minutes, 32 seconds into it's journey...)