4 ms·

The obvious solution seems to be to technically enforce the speed limits without relying on average-speed-through-section, which seems to have been done way too

The obvious solution seems to be to technically enforce the speed limits without relying on average-speed-through-section, which seems to have been done way too late. Likewise, the yellow signals could trigger enforcement of a braking curve to ensure the train will have a sufficiently low speed at the next red signal. (This is how one of the German systems works - PZB, not a modern one either, I think the braking-curve-enforcement was introduced in the 1950s.) Especially if the "too much acceleration" problem only applies to new trains, that also conveniently addresses the upgrading issue - old trains accelerate slow enough to be safe under the old rules, new trains can have e.g. a speed limiter. It's also just one subway system, not an entire national railway network, which should make modernization a lot easier. But I guess given that apparently actually using regenerative braking was a new thing in 2018 (https://www.progressiverailroading.com/sustainability/news/MTA-to-test-energy-reduction-technology-on-subway-system--55935 https://www.progressiverailroading.com/sustainability/news/M...) despite the heat issues in the stations, I guess that's expecting too much.

pantalaimon 4y ago
PZB was already introduced in 1934 https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussung https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...
- usr1106 4y ago
  The previous commenter did not say PZB were introduced in the 1950s, but adaptation to braking curve. Not an expert in the area, but I very vaguely remember that 1 out of 3 braking curves is selected for each train. Not sure how big the risk is that trains would operate under the wrong braking curve and whether that has ever materialized in form of an accident. Edit: Selecting a braking curve seems important when the same engine can haul passenger trains and freight trains. That was rather common in Germany decades ago, probably less so today. Doesn't seem relevant for EMUs like on the NYC subway.
  - iggldiggl 4y ago
    Supervision of actual braking curves through PZB was actually only introduced starting in the mid-80s (first version of the PZB implemented through microprocessors), and widespread retrofitting of older rolling stock with an upgraded PZB-version only began in the late 1990s/early 2000s in response to the Rüsselsheim rail crash. Before that, speed control only happened at discrete points along the lines of "speed must be lower than x kph after y seconds", so you could actually continue running at full speed for up to y seconds before tripping the train protection. Meanwhile, the currently existing lines on the two pre-war Underground rapid transit systems in Germany (Hamburg and Berlin) are still using simple train stops, too (though they did at some point upgrade to magnetic/inductive train stops instead of the original mechanical train stop system).

pantalaimon 4y ago

PZB was already introduced in 1934 https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussung https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...

usr1106 4y ago
The previous commenter did not say PZB were introduced in the 1950s, but adaptation to braking curve. Not an expert in the area, but I very vaguely remember that 1 out of 3 braking curves is selected for each train. Not sure how big the risk is that trains would operate under the wrong braking curve and whether that has ever materialized in form of an accident. Edit: Selecting a braking curve seems important when the same engine can haul passenger trains and freight trains. That was rather common in Germany decades ago, probably less so today. Doesn't seem relevant for EMUs like on the NYC subway.
- iggldiggl 4y ago
  Supervision of actual braking curves through PZB was actually only introduced starting in the mid-80s (first version of the PZB implemented through microprocessors), and widespread retrofitting of older rolling stock with an upgraded PZB-version only began in the late 1990s/early 2000s in response to the Rüsselsheim rail crash. Before that, speed control only happened at discrete points along the lines of "speed must be lower than x kph after y seconds", so you could actually continue running at full speed for up to y seconds before tripping the train protection. Meanwhile, the currently existing lines on the two pre-war Underground rapid transit systems in Germany (Hamburg and Berlin) are still using simple train stops, too (though they did at some point upgrade to magnetic/inductive train stops instead of the original mechanical train stop system).