…I believe the “jolt” one felt on whatever passenger trains was the skill or care the way the engineer put the power to the rail to start the train…Maybe the heck with being smooth…“I’m late, and this thing has got to move”…
Here is the “official” answer, direct from cartalk.com
RAY: When a train is moving along the track, the coupling, those parts that hold the cars together, get stretched out. They have the ability to compress and then decompress, so to speak.
When a train is moving slowly stops, a situation exists where all the couplings are pulled out against each other, so that if the train were to start up again, it would be moving the last car at the same instant that the locomotive started to move. In essence, it’d be like one big car is being moved.
Now even though locomotives are very powerful, if the locomotive tried to move all the cars at once, it would be unable to move them. So, they back up the train and compress the couplings, one at a time. When they go forward again, the locomotive has to move only one car at a time. So, the train moves the first car, then the next car, as each coupling gets stretched out, so that by the time it has moved a number of feet, the last car starts to move. In other words, all the cars don’t have to get moved simultaneously.
So who’s our winner?
TOM: The winner this week is Tom Kanouse, from Sherwood, Oregon, and for having his answer selected, at random, from among all the correct answers that we got, Tom is going to get a $26 gift certificate to the shameless commerce division of cartalk.com, where he can get our brand new Car Talk baseball jersey, just in time for spring training.
Back in the in the steam and friction bearing days, taking slack was about the only way to start a train. Steam engines, by design had very low starting tractive effort and friction bearings have natural “stickiness” to them compared to roller bearings when not rotating. That is, it take more force to get them rolling from a stop than a roller bearing. So, getting a train moving car at a time was a normal technique to get a train rolling.
But in the diesel/roller bearing era, things are different. Staring tractive effort is what DC diesel-electrics do best (and AC units do even better) and roller bearing don’t take much force to get them turning, so is is possible to start long heavy trains w/o taking slack. In practice, it allows slackless or nearly slackless trains. Think Roadrailer, ATSF “ten packs” and 5 well stack cars.
There are times when the train is too heavy or the power is mismatched when taking slack to get rolling is can still be a necessity, but it isn’t std practice these days like it was 60 years ago.
Headed to the couch for time out. If its any consolation, I just left a meeting not too long ago and managed to walk away with a pad full of little trains driving around. I’m not sure what the meeting was about anymore…sigh[zzz]
In modern day trains of today I leave my train streched for the perpose of leaving fast. If you have slack in your train you haft to leave slow to strech them so you dont get a knuckle. if they are streched tight like on a hill you just get notches and keep pulling no need to work out the slack. or worry about a knuckle. to take slack to move the train is not common practice anymore.
…How about a railroader stepping up and answering whether passenger trains do or do not have slack built into the couplers…As I mentioned above, I don’t think they do, but lets hear the voice of the trade.
A very little bit; just enough to allow the moving parts of the knuckle to open and close. But even that small amound can seem like lots in the hands of a lousy engineer.
On the CNW, we ran push-pull suburban trains. Back before Metra went to all F40PH’s, we ran F7’s & E8’s, which all had a “quick-start” switch (this caused the load regulator to move to maximun field when the locomotive was in ‘idle’). When operating from the cab-car, one had to be very careful not to release the brakes too fast as the throttle was opened. We usually kept about 25psi of brakes set when stopped at a station. When the throttle was put in the first notch, the loco would bump up against the coaches with their brakes firmly set. This resulted in a nice smooth start. If insufficient air was held on during the stop, the motion of the loco banging in to loose-rolling coaches had the result of sitting down anyone that was still standing, and also causing many cups of coffee to be spilled. Experienced commuters knew not to drink during a station stop until the train was moving. The good engineers also knew at which stations the slack would run-in during a station stop when running from the locomotive. Easy throttle advancement was necessary then, too.
And all this “slack action” occurred in trains of only 3-8 coaches!
BTW-all passenger cars (and locomotives) have the “lock-tite” type of knuckle. It is similar to the type seen on haz-mat cars.
…Zardoz: Thanks…for comprehensive answer. I suppose the engineer making a smooth start and not so smooth start might be compared to a good aircraft landing and the other kind…So, I suppose if a passenger train of say 20 cars was in control of an engineer in a hurry, the rearmost passengers might get a pretty good kick on a hurried start.