How come certain stations at 34th St (A/C/E and 2/3) have it set up so that you can't cross the platform to get from the express line to the local? You actually have to go down and up stairs to get to the express line from the local. It doesn't make sense.
As regular riders of the A, we always see confused people at the Penn Station subway platform, especially late at night, when the express stops running, and misguided people stand on the express track and begin panicking as the A goes by on the local track.
The Straphangers come to the rescue by explaining that the platform design at 34th Street is to control crowds. Anticipating crowds from LIRR traffic, the express and local trains are on separate tracks to avoid overcrowding. (The west 34th Street station is the 3rd busiest station in the system.) NYCsubway.org confirms:
Four tracks, two side and one island platforms. The two side platforms are used by the local trains and the center island by the express trains. This arrangement was planned to discourage transfer between local and express due to anticipated high volume.
Interesting trivia: New York's four track system (one in each direction for express and local) was the first of its kind, and back in the early days the express could traverse the length of Manhattan in 26 minutes, with trains going about 45 miles per hour. We think now the trip on the A from 207th St. to Fulton St. (one end of Manhattan to the other) would take about 50 minutes. The A is also the longest line in the system, and have been told that going from one end to the other takes about an hour and a half (although we haven't actually tested this, so we don't know first-hand).
Related: All kinds of subway weirdness and ephemera at Forgotten-NY.