One of the articles I linked to is about a bus that high-centered on the tracks before being struck; it’s true the driver ignored warning signs, but it’s presumptuous to assume his now-deceased passengers were of similarly limited intellect.
Likewise for this incident, in which a truck bearing a trailer full of veterans to a parade was struck, with a number of said veterans dying.
Even if a driver makes a dumb mistake and endangers only his/her own life, that life still is of value and deserves protection; you may come to appreciate this perspective if/when a close family member ever makes a dumb mistake and endangers his/her life. That’s why we have things like guard rails, electronic stability control, seat belts, and so on.
Indeed, I specifically addressed this in my OP as the motivation for considering whether simply locking the wheels might be a more viable alternative (and I think we’ve now shown it not to be).
:smack::smack:
I did some mental math and came up with an average speed of 30 MPH. The “30” somehow jumped the track and ended up in the “elapsed time” category.
Many streetcar and light rail systems use electromagnetic track brakes for emergency situations. Track brake - Wikipedia I don’t think they’ve been used on mainline freight railroads because there isn’t a high voltage electrical connection between cars, but maybe some passenger trains have used them?
In response to several posts;
Yes, with only a few very rare exceptions, all of the wheels on every car have brakes. These are (on freight trains) shoes that press on the outside of the wheels.
Yes, locking the wheels increases braking distance considerably. The dynamic braking which many if not most mainline locomotives have works by feeding the current from the motors-turned-into-generators into a resistor bank. They only work down to a few miles/hr, and generally cannot actually stop a train. They are mostly used to control trains on downhill sections. Dynamic brakes are only on locomotives, except for the special case of some subway cars. The cars in passenger trains have essentially the same system as freight cars.
Slack action is something to be feared and managed, with trains over a mile long on rolling terrain there may be parts of the train going uphill and other parts going downhill. It takes certain amount of skill on the part of the engineer to handle this.
Why do they take a long time to stop ? Because they have very limitted suspension and -1.3 to -2 m/s/s is about all they can take! What will happen if you try harder ? The rear end of the carriages lift up ! If you jam the brakes on harder you will derail way way before locking up the brakes.
The emergency brake setting is enough to cause people difficulty standing up or remaining sitting on their seat, any harder and remaining sitting with seatbelts would be required, however that would also require the suspension upgrade to handle the deceleration.
And in answer to Constanze, yes, the locomotives have sand available for traction, but only the locomotives have sand. You would not normally use sand for braking unless the rails are slippery from rain/snow/whatever.
There is also a distinction between regenerative braking and dynamic braking. There is also a big ass fan to cool the resistors. Sometimes (not around table flat here) you can hear the blower cut in and out. The latter is just the motors converted to generators and the power fed to a bank of resistors. Regenerative braking sends that power back into the supply grid, which obviously only works where there is a connection to the grid, i.e. electric locomotives or MU trains, such as subway cars. In the DC metro you will often hear a sort of a rrrrriiiiing sound as the train stops—that’s the regen braking.
Not all of the crossings. Probably not even half of them are controlled crossings. Remember that in masny parts of the rural area of the western US, there are gravel farm roads every mile, and any railroad will cross many of them.
And in the USA, they aren’t even all required to even have a static sign for 3 more years.
I’ve seen track brakes on (American) Pullman cars. Don’t think they were electromagnetic: don’t know what they are used for. From memory, “point of contact” was about a yard long?
Perhaps a way to increase stopping force would be to have opposing wheels on each side of each rail that can exert pressure and braking force. This would allow much higher force against the rails for braking than the weight of the train alone.
This isn’t the problem. The problem with brakes failing is when they overheat. Somehow you have to get rid of the kinetic energy of the train - and that isn’t a small ask. Brakes do this by ridding themselves of heat into the air. If they overheat they start to develop gas in the contact area between the pad and the wheel (or disk rotor.) Keeping them cool is the key. Anything that keeps the pad temperature down will allow you dissipate more energy. Just increasing adhesion to the rail doesn’t change the rate you can dissipate the energy.
Some years ago I contributed to this thread about Casey Jones and wanting to stop a train a quickly as possible. Things have been improved in the century since Casey but the basics are the same.