Quote Originally Posted by 3WC View Post
It's true that there are regularly scheduled, fast trains between ORD and downtown Chicago, but there are probable a million people living in downtown Chicago. Those trains run every half hour or so and run above-ground, between east and westbound freeways.
Duggan is trying to address a specific problem which was not well described in the article. Due to the way DTW is built, if there were to ever be a commuter rail service between Ann Arbor and Detroit, the only way to connect to the actual airport terminals would be to build a tunnel from the tracks to the terminals [[he is NOT talking about building a subway from the airport to downtown Detroit).

The tunnel would need to go under the runways. In other cities, the connection between airport terminals and regional railways is sometimes done using automated trains running on elevated tracks, similar to Detroit's PeopleMover. This would not be an option for Metro because the elevated tracks would have to go over the runways to reach the terminals.