1900 vehicles per hour per lane is slightly less than 2 second spacing.
I also remember that "C" shaped curve of capacity. It explained why, for a highway running near capacity, one day you can sail along 40-50 mph and the next day, you're stuck at 10-20 mph - with the highway carrying exactly the same traffic. Once a jam nudges you under that "critical" speed, it's game over!
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Nice post. I grew up in Philly and went to Girard College, which was really an orphanage for grades 1 to 12. I lived there from 1947 to 1957. Your route on the number 15 PCC trolley took you right past the school's main entrance just west of 20th Street. I rode that line many times to get to the Broad Street subway.
Jack
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