Another Continuum

In my head – and I suspect in most people’s heads – there is a sharp distinction between subways and similar mass transit and other heavy rail. Light rail, particularly street cars running on a shared right-of-way seem like a third different thing. But in reality, the differences get very blurry the longer you look. Boston’s Green Line, for example, is about half subway and half street car. One of the blurry differences concerns branches. On long-distance railroads (including commuter rail) where trains on any branch are spaced half an hour or more apart, having a bunch of switches to shunt trains onto the right branch is not a problem. On a busy mass-transit subway, where trains might have headway of only a few minutes during rush hour, every switch movement is a potential delay. This might seem obvious now, but older el and subway systems were designed more like railroads. Here’s Max Hubacher’s 1951 photo of the somewhat insane rail layout at Broadway Junction in East New York,…