|Notes: line width is proportional to ridership. Lines are grouped by color. Green = NJT. Yellow = NJT operating in to New York. Blue = Metro North. Red = LIRR. The chart will definitely make more sense when referenced to the original post.|
It does seem that lines which were once or are now major intercity routes are more likely to have longer-distance commuters and look more like intercity trains. The four lines in this group constitute the three main lines which operate frequent intercity service from New York (the LIRR doesn't have any cities to operate to, of course) to Boston (New Haven), Albany (Hudson) and Philly/DC (NEC). Of course, even though the Metro North in Connecticut serves trains to Boston and Springfield, it is still painfully slow with maximum speeds of only 70 mph, half the speed of the NJT NEC towards Trenton.
Anyway, I think the chart looks pretty cool. (Next up: giving the same treatment to Boston's trains, and whining about the MBTA's commuter services a bit.)