Timeline for Why did the metro bus stop at each railway crossing, despite no warning indicating a train was coming?
Current License: CC BY-SA 4.0
22 events
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| May 15, 2019 at 15:22 | comment | added | R.. GitHub STOP HELPING ICE | @JaccoAmersfoort: The detail is actually needed to shut up the folks in denial about reality. | |
| May 15, 2019 at 14:52 | comment | added | Harper - Reinstate Monica | @JaccoAmersfoort If I reduce it to your level, it becomes a hollow finger-wag. I have already pushed most of the detail into asterisks, and at your request, I've pushed some more. The purpose of asterisks is to allow you to skip detail you don't care about. This is a technical forum and most people want details to be accessible, * is a fine compromise. | |
| May 15, 2019 at 14:44 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| May 15, 2019 at 9:35 | comment | added | Jacques | This answer is much too technical to be useful. You could have just said "the train cannot stop in time so the bus is extra careful" which is the gist of your answer, but you made it convoluted with the numbers | |
| May 15, 2019 at 3:05 | comment | added | CJ Dennis | Even a long freight train can come to a complete stop in 1/4 mile if its speed is low enough. | |
| May 15, 2019 at 3:04 | comment | added | CJ Dennis | Stopping distance normally assumes braking is linear, which combined with time gives the square rule: stopping distance is proportional to speed squared. In 1/4 of its stopping distance, it still has 75% of the distance to go. The square root (since we're going backwards from distance to speed) of 75% is ~86.6%. That means ~13.4% of the speed is gone. In half the stopping distance, only ~29.3% of the speed is gone. In 75% of the stopping distance (25% remaining), half the speed is gone. | |
| May 14, 2019 at 17:56 | comment | added | Harper - Reinstate Monica | @J... However the people who have implemented ECP are not the people who run 20,000 ton trains. "20,000 ton" is not an arm-wave | |
| May 14, 2019 at 15:35 | comment | added | J... |
*** Yes, it can go faster than the speed of sound (in air). More and more trains, especially passenger and very large, heavy freight trains are using ECP brakes which make use of electronic control signals to actuate all brakes on the train effectively simultaneously (rather than the old vacuum/pneumatic controls which could take 10s of seconds to propagate to the rear of the train). This improves braking, preventing the rear cars from heaving forward into the front cars while the brakes are being applied.
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| May 14, 2019 at 14:43 | comment | added | pipe | @Therac You should write an answer to OPs question if you have information not previously covered in an answer. | |
| May 14, 2019 at 14:16 | comment | added | Sanchises | @Harper Friction brakes are constant force devices (they deliver roughly the same amount of force regardless of speed, namely the friction coefficient times the normal force on the brake pad), which means they dissipate more energy per unit of time when braking at high speed. However, when braking at high speed, you also cover more distance per unit of time and as it happens, the time cancels out and the amount of energy dissipated is proportional to force multiplied by distance. | |
| May 14, 2019 at 14:03 | comment | added | Harper - Reinstate Monica | @Sanchises energy dissipated is proportional to time. Brakes don't care about distance traveled. | |
| May 14, 2019 at 13:41 | comment | added | Therac | @pipe A car is: 1) Much quicker to evacuate (more doors per passenger), 2) Its owner's responsibility and not a common carrier, and 3) Very unlikely to be a danger to the train if hit, unlike some heavier commercial vehicles. | |
| May 14, 2019 at 10:12 | comment | added | Sanchises | Your **** footnote confuses some things. It's true that in 1/4th of the distance it will not slow down 25%, but that's because it's simply going faster initially, covering more distance while it is slowing down. The energy dissipated by the brakes is actually proportional to braking distance, and the energy dissipated into mangling the bus is proportional to the kinetic energy (assuming perfectly inelastic collision), which means that after 1/4th of the braking distance, the bus will be 25% less mangled. | |
| May 13, 2019 at 15:51 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| May 13, 2019 at 15:41 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| May 13, 2019 at 15:34 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| May 13, 2019 at 15:30 | comment | added | Harper - Reinstate Monica | @pipe ok fixed. Issue is level of potential calamity. | |
| May 13, 2019 at 15:29 | history | edited | Harper - Reinstate Monica | CC BY-SA 4.0 |
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| May 13, 2019 at 15:21 | comment | added | pipe | I'm referring to the actual question. OP wonders why the bus had to stop but the cars didn't have to. "Other cars didn't seem to do this". You only focus on the train. Can the train stop faster if a car approaches? | |
| May 13, 2019 at 15:18 | comment | added | Harper - Reinstate Monica | @pipe I don't believe I mentioned any cars. Are you referring to automobile cars, or train cars (segmented units of a train)? | |
| May 13, 2019 at 10:59 | comment | added | pipe | Fails to answer the question about why the cars won't stop, though. | |
| May 12, 2019 at 22:56 | history | answered | Harper - Reinstate Monica | CC BY-SA 4.0 |