I find the different physical characteristics of different rapid transit systems interesting. For example, Chicago still uses an old-style inner and higher third rail, used by Manhattan and Brooklyn elevated lines in the past, where as New York uses essentially the same third rail that the Long Island Railroad uses and that PRR used for initial Penn Station electrification. Ditto Hudson and Manhattan, now Port Authority Trans- Hudson or PATH. But the biggest difference between Chicago and New York is the characteristics of the typical junctions, where two lines join. With possibly only two exceptions, Chicago's are all flat junctions, which means there are opposing moves. The two exceptions are in the Congress Expressway, where the branch to Douglas Park leaves the Congress line without any conflict, and south of Loop where the State Street subway and elevated south from Roosevelt Avenue join and then separate to feed the Dan Ryan and Englewood-Jackson Park lines. Other than that, all flat junctions. In New York City, the most recent flat junction was built around 1917 at Myrtle Avenue and Broadway in Brooklyn. The "M" now separates there from the "J" and "Z". It and the junction that was part of the original 1904 planned construction, north of the Lenox Avenue (pardon me, Martin Luther King Boulevard) and 135th Street Station, where the 2 branches off from the 3 to go to the Bronx are the only two flat junctions on the NY system. But Chicago put in new flat junctions recently at both end of the revised Paula connector for the Pink line.
Any explanations?
The junction where the Douglas Park line splits from the Congress line was built as a flyover due to the grade separation involved when the Congress line replaced the Garfield Park line in 1958. It was originally a flat junction. The only other flyover on the CTA is at 18th Street where the Midway (Orange) line splits from the South Side Main (Green) line. The junction of the Paulina connector with the Lake Street line was always a flat junction.
The reason for flat junctions on the Chicago Rapid Transit is probably due to finances and the law. The finances of the four original rapid transit operators were quite tight. In order to build an elevated railroad over city streets, the companies had to obtain signatures from a majority of the landowners whose properties faced the streets. So you either paid for the signatures or bought land for a right-of-way not over city streets. A flat junction required less land than a flyover.
But the old Chicago Rapid Transit did have one grade separated crossing! Interstingly enough it was at the north end of the Paulina connector, at Paulina and Lake. Now a flat junction and not a crossing. Wonder what will happen if the full crosstown rapid transit construction proceeds! I suspect it will be level crossing!
The remarkable thing is that with all its flat junctions, rush hour headways between trains on the CTA aren't much worse than on New York City Transit System. If one were to look at just one diamond at Lake and Wells, what is the effective headway between trains in both directions? I suspect it would about fifty seconds, the tail of one train clearing the diamond perhaps 10 or 15 seconds at the most before front of the next enters.
Other than Chicago's CTA, possibly the only other location for that sort of density on a flat crossing is at Coply Junction on Boston's Green Line, but light rail cars can stop on a dime with magnetic track brakes. But then, possibly one difference is that CTA uses magnetic track brakes? Or do they? I don't remember and would appreciate a refresher. New York never has except possibly on one or two of three experimental lightweights of the 1930's. (The aluminum Pullman "Green Hornet.") And of course on the 100 Brooklyn PCC streetcars.
CTA has used magnetic track braking beginning with the 6000-series cars in the 1950's since these cars used PCC technology.
Since 18th Street Junction (originally for the Dan Ryan Line and now used by the Midway Line) was built as a flyover in 1969, I would assume that any future construction would involve flyovers if not constrained by space considerations.
daveklepper wrote:Is there room south of Paulina and Lake for a flyover?
Since the Lake Street line is directly over the street and the street frontage on Lake is built up, there isn't any room for a flyover.
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