And finally I'll give some context for Concept 1, the tunneled APM. IMO the cost of this option is wildly underestimated, the study essentially presupposes none of the following issues will be factors:
SANDAG decided not to add a cost contingency for these partially because it's extremely difficult to estimate without doing a lot more study, and partially because some of the the worst case scenarios looked really,
really bad ($1-2 billion+ in additional costs).
Also the 3 minute travel time doesn't include time spent going up and down to reach the tunnel entrance 80 feet below grade. An escalator will add 1 1/2 to 2 minutes each way (which gives the total time of 6-7 minutes from Grand Central Station to Terminal). Elevators would be slightly faster, but have capacity issues.