i realize that the grade on the main line needs to be low enough that your longest trade can handle hit, this it typically 2% and may need to be less on curves.
but i would think that on a spur that is several feet long, where only a few cars need to be handled, can be much higher (> 4%).
a side question is even when a spur eventually is higher than the main, is it made lower near the main so that car would roll into the spur rather than onto the main. (I realize that a car coming from the end of the spur would probably have enough momentum to roll up onto the main).
Normally the mainline would be protected by a derail. Think of a roller-coaster… a little hill is not going to stop something coming down from a bigger hill.
In practice, almost every spur that connects to the main line will have a derail. At the Red Trail Energy plant it is because the plant has two locomotives of its own shoving cars around. BNSF only opens the derails when THEY want to move cars on and off of their main line. But in all cases, there is no telling what some one at an industry may do and leave a car with the brakes not properly set.
Yes, a short grade can be steeper. The problem with it being on a spur is how do you keep them there once you spot 'em? If it’s downhill from your running track, it’s easy, just put a bumper in and let them accumulate against it at the bottom.
But if it’s downhill on the spur to the switch, then you need something other than an emergency device (derail). Since our models don’t have handbrakes, then you need to provide something to hold the rolling stock in place once spotted. The end of a choke cable sticking up between the rails is one way.
If you are going to handle a small number of cars, almost any loco should be able to deal with four or five percent grades. My coal hauler has a 4% standard grade, and a couple of 350mm radius curves with uncompensated 3.51 percent grades. Granted that I need one powered axle for every two unpowered axles, but the grade is workable.
If you do build a roller coaster, remember that the place where you park a car has to be flat, or on a downhill slope to a bumper at end of rail. In addition, a nylon brush bristle or two, planted vertically in the space between the ties, will help persuade cars to stay where you put them.
For a really steep downgrade to a mainline switch, the prototype sometimes uses the equivalent of a runaway truck ramp. The mainline connection is built as a crossover, with the straight route off the mountain leading to a short spur, usually upgrade from the frog onward, where the rails are covered by a mound of gravel. My prototype had that arrangement at virtually every station.
In the narrow gauge world, 6% grades on spurs and switchbacks can be the norm. Traditionally, there is a level or very slight dip at the peak or business where the cars are usually spotted for loading. Even on narrow gauge lines, the mains are protected, often with a derailer, but the issue is usually moot as runaway cars are easily derailed at the end of the first switchback well off the mains or on one of the many sharp curves found in such switchback operations. While runaways did occur, it was rare due to the nature of the switching operataion and the level or slightly dipped spotting area.
Few if any mines or mountainous quarries ever had their own motive power and thus all cars sat where they were spotted as empties, filled there and awaited the pick up engine’s return on another day. Operations at the mines or quarries were small, quaint, mom and pop operations and a big string of cars might be 5 cars. A few of the largest operations used capstan pull engines to move the cars deeper into the level loading area. Again, no runaways possible here either. Narrow gauge cars were constantly hand wheel braked hard-on once spotted or on a partially applied “drag-brake” when capstaned. (Narrow gauge brakemen worked their butts off!)
An 2-4% elevated spur with a switch thrown into a, very large, blind incline of 8 to 10% would prevent a runaway from derailing, but be far more expensive to the railroad than a simple derailer. This might be a novel thing to model.
That is exactly the opposite of what I’ve built, but it makes the point perfectly.
Not very likely that a car parked at that builders’ supply will roll across the road and onto the main…
Richard,
Many mines in places where the terrain stands on edge have a very simple, straightforward way to move empties under the loadout and loads to the outbound yard. It’s called gravity - and it never breaks down, calls in sick or goes on strike. It DOES require that the mine employ some folks who know their way around a brake wheel.
The only place I’ve ever seen a capstan in use was as flat as a well-leveled table. The cars being moved were loaded covered hoppers which had to be mated to a single discharge connection.
