I know that locomotives come equipped with sanders to assist adhesion, but I’d bet that the sand gets swept off the rails pretty quick in an emergency stop situation. How does rain soaked rails affect the stopping distance of a typical freight train? (all other things being equal)
I don’t have any facts or figures to help with the stopping distance. I’ve never really noticed any appreciable length in stopping distance on wet rail other than maybe when in switching operations. It does effect power and dynamic braking efforts to the point that sand can not prevent slippage.
Now SNOW is a different problem altogether. The fact that snow can build up between the brake shoes and the wheels can cause catastrophic problems if preventative measures are not taken in route and before preparing to stop.
good question. i’ve never thought trains would hydroplane, but i could see how wet rails might cause traction issues
No the sand does not get blown off the rail in an emergency brake application. It gets crushed between the wheels of the loco and rail though. It is stuck pretty good until a few cars get over it and knock it off.
The water on the rail does not really affect the wheel/rail adhesion very much except with the locomotive wheels. Especially in dynamic braking where the loco wheels may start to slide at which point the wheel slip system backs off the dynamic braking to allow the wheels to turn again so as to reduce the likelihood of flat spots forming.
Where the moisture is a problem is when it acts as a lubricant between the wheel treads and brakeshoes on the freight cars. Such moisture, especially when the temps are low enough to make this sort of a sleet type of mixture, can reduce braking effectiveness by as much as 30% according to some sources I have seen. As the brake shoes and wheel treads heat up the moisture drys out upon contact and normal braking distances are restored.
Provided, as Big Jim pointed out, it’s wet or sleety and the brake pressures are enough to get the shoes in contact with the wheels. If it’s really snow, or heavy, and the shoes can’t contact the wheels, or it builds up on the rigging so that the shoes can’t move, you are basically out of luck. No contact, no heat, no melt… it’s a good time to jump. Of course, if you’re on the ball, you noticed the problem earlier, and gave it 8 pounds or so from time to time to keep things free. You did, didn’t you?
There you go[tup]
I know of a couple of runaways because of snow pack. The simple explanation is to think of why an ice skate works. Pressure pushing down on the skate melts the ice into a thin layer of water. The skate then glides on this thin layer of water. Same thing happens with brake shoes and wheels. Whoops, that’s slick!
It maybe surprising to the non RR’ers, but just a thin coating of frost can cause a train to stall on a hill. Rain is much better than the frozen stuff.
BTW, I was bringing back a set of light units one day after a quarter inch or so coating of freezing rain. The problem wasn’t that it was slick, no the wheels would break the ice. The problem was because of the friction breaking the ice. Where I would normally cruise in the third notch, it would instead take the fifth notch in order to break the ice and run track speed.
If we painted “kills” on the sides of locomotives like WW2 fighter pilots did, I would have an enginehouse shop door on my machine . Ice+ snow+SD-45+complacent operator= crash.
There were some other similar incidents in my career but I think I could still be prosecuted so they will have to wait for another day .
Same thing in the OTR trucking industry. We hated ice with a passion and heavysnow. It would jam up our brake rigging and we would be in a world of hurt. Try picking up a trailer with 3 inches of ice on the brakes needless to say I was under it with my short handle 3 lb sledge hammering the brakes to get them off. Then hitting the S-cams to free them up to make sure they would move. Rain is liquid and will move easily ice is solid and has to be made to move first before you can do anything snow is right in the middle.
Almost correct.
http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/1998/ice2.htm
http://www.universityscience.ie/pages/scimat_Explaining_ice.php
http://users.hubwest.com/hubert/mrscience/science12.html#slippery
Well, Mr. Salmeron, just go and try to tell that to my GE Dash-9!
Well, golly. I guess I will have to keep an eye out for that as winter approaches. Maybe I have never experienced that in 30 years of train and engine service in Montana, Idaho, Washington, Nebraska, Wyoming and South Dakota.
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These are good web sites, and I have read other articles like them about ice and its surface effects. However…
At some temperature about -15 deg Fahrenheit the behavior of snow and ice changes. The ice on a pond, even when it is very smooth (black ice), is much less slippery to walk on, and it is difficult to skate on. The skates will go, but they make a wierd scratching noise and feel held back. Walking on snow below that temperature produces a high-pitched squeak, instead of a crunch, and the snow also is much less slippery to walk on.
I have personally experienced these effects when I lived in New England. None of the recent articles mention them, so I am not satisfied that we have the right answers yet.
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I see, thanks to all who replied. They always say that the minimal friction of steel wheels on steel rails is what makes rail transport so efficient. SO I was just wondering if the rain slickened rails made the friction even less, to the point where stopping distance was affected.
…cordon: I’m with you on the comments of snow and ice at the temp you mention…{-15} degrees…or so.
Home area is in western Pennsylvania and have experienced it too.
Back to the rain.
Considering the pressure between wheel and railhead under even light railroad equipment, I doubt that the rail stays very wet under a passing train. If the motive power doesn’t slip-stall, by the time a half-dozen freight cars have gone by the railhead is probably as dry as the Dessicated Desert. Given that, braking in RAIN (not sleet, heavy snow or built-up ice) shouldn’t be very different from braking in bright sunlight.
Chuck