Downhill speed

Yep,  I use diodes/bridge reçtifiers to drop the voltage along mine.  

Not active right now, but a track pressure trigger at the upper level triggered a relay to add or remove them.  I barely need 6v for anything downhill.

I replaced this with a Z . Each dial(4) is one block. But the up and down blocks usually get set then left alone. Actual throttle change is done mostly on the level portions vs on grades.  The 4 blocks are , grade#1, upper level, gràde#2, lower level.  It allows for handsfree looping no matter what I run.  You have plenty of time while on a grade to grab either upper or lower throttle.

Test that curved grade asap. Curves are best done flat or with little grade.  It causes a twist and some locos (esp. 6+ driver steam)can't keep all wheels planted. It needs super elevation to stay planted. (think of a roller coaster. It either tilts in curves or curves flat, then climbs/drops after the curve.)

The idea could be modded to give or take X volts from the initial throttle setting (basically three levels from one setting, location dependent.)

There are 2 issues to solve. 

1) Creating a source of lower track voltage other than by manually lowering the throttle handle.  To that end, take a look at this OGR thread. 

2) Triggering when to swap-in and swap-out the lower voltage.  This is the classic occupancy detection problem with the list of usual-suspects - insulated-rail with relay, pressure plate (e.g., Lionel 153C), Infrared/optical detector (Lionel 153 IR), and so on.  Details such as specifying if train run both directions (i.e., don't reduce voltage if entering grade going uphill) will narrow the choice.

That is a steep grade.   If the 54 stuff has magne traction, it should not be a problem.    If the 48 is like my 726 berk, it will roll very fast down that grade and voltage will have to be reduced to maybe 6V or less as mentioned above.

OK, using Stan’s 2 points as an orgazing principle for this discussion. 
I understand the need for some kind of triggering device. If placed on the circle of the dogleg before the track joins the down hill run I guess that could work. I’d have to program the O22 switch so it always returned to the first position so the that on its way back up the grade the train doesn’t hit that trigger while the consist is still coming uphill. 

But the whole discussion of Doods and rectifiers in #1 and the attached string is way beyond my experience or understanding. You’ll need to take me back to first grade on that. 
I have figured out how to reduce my grades slightly. Two of my locomotives do have magnatraction. 
thanks for help with this. 

Re:  Stan’s first point, creating a source of lower track voltage, an acquaintance who operates a two layer 13 x 27 foot empire suggested the use of as resister with an insulting pin in the central tail as a trigger.  I can’t see how that would work on a track that runs both up and down with a dogleg. 

It might help if we knew more about your controls and space used. You threw me with "program an 022".... in particular "program" ...Trigger?  (time to only call them turnouts so "switch" can be used in electrical or verb context without confusion)

This is two reverse loops connected by one line, or a siding with a grade and reverse loop? (I guess it would just be repeated on each end, but Im having trouble following you as well, e.g.    No picture or track diagram to use to avoid some of those 1000 words? It helps tons IMO.

Magnetraction has little downhill effect compared to non-magnetic on mine. But as a note, my line normally has a designated loco with Magnetraction on it. If anything, it takes less voltage than others. But that is normal for that loco. Other locos of both types need more than 6v and ive not noticed much difference between non/mag and mag locos to even make note of it.

A pair of diodes, wired bands opposite, back to back, legs tied.(opossed but parallel) Now those, inserted into the center rail wire(series) will lower voltage 0.75v, two pairs in series = -1.5v etc.  This will not lower amps (good)

But a resistors effect will vary both volt and amp, and at various rates depending on input/draw at the moment.  The ceramic resistors, much larger than diodes too.

  So diodes are a very cheap & simple way of lowering voltage but leaving amps for use. Resistance will drop both. Ok, but I like the diodes better overall. 

So, you have regular power, and need three levels total. Regular power will = high (say 15v), 3 paired diodes(6) added = med. for level track -4.5v (10.5v), and 6 paired = low -9v (6v)... one feed split into 3 feeds.  Now to distribute them.  (switches can vary the number of diodes dropped/added at the moment too)

Trigger method is almost redundant.  You need to auto-drop or raise the volts on  blocks containing grades. A relay will do that and it could be triggered by various methods.  Placement location of triggers and why are of far more importance than how.

Some pushing or pulling needs extend beyond the visuals of grade vs straight. E.g. climbing a grade, you still need a power increase beyond the peak and onto the elevation because the loco is done climbing, but the train is still on the grade being pulled out of the hole.

  Becuase of this two additional blocks at the far ends of the elevated sections might work best for you. These would switch between hi/med.

 It's also why a diagram is MUCH easier to work from. Distances, points, consist lengths can impact where or if some triggers and blocks are even needed. 

Push of cars during decent isn't as big a factor because you usually have the loco near drop out voltage anyhow, you really can't slow more. You want command control and dynamic braking if you want more low end control than that.... or less cars.

So... on the el. block #1 , el end by peak #2, grade #3, rev.loop #4  (mirror if there are two rev. loops & two grades) 

Blk#1 med pwr, blk#2 sw/med.& hi, blk#3 sw/lo&hi, blk#4 med.

Loco on #1traveling to #2:  #1 trigger sets #2 to med(no loco change), loco passes #2 and #2 trigger sets #3 into low. loco enters #3 and slows decending. At block #4 power is med. always just as #1 so Loco returns to normal speed. On #4 trigger moves #3 and #2 to hi to climb out.  Once on #2 again#3 is switched back to low, but loco is past it.

The limiting factor is how long the train might be. It can't be longer than the distance between the two grade triggers on #2 and #4.

Drawback is lighted cars will dim or grow bright depending on position on the layout. Lighted cars may need mods so they don't bridge block power, feeding a low pwr, with hi pwr up one roller across the bulbs and out the other roller. (single roller lit cars don't have the issue)  Fast acting polyfuses can be placed in dual roller cars to open so only one works for a split second until both are on the same track.

I'm gonna stop and see where this goes.

If messing with diodes, rectifiers and the like is gobbledygook I'd go with a rheostat as suggested earlier = see posts in the linked threads by ADCX Rob.  That would be a simple 2 terminal connection, no soldering, etc.  The Lionel rheostats go for around $10-20 on eBay and there are dozens for sale right now.

As for the triggering, I agree with you that insulating pin(s) alone will not work.

I'm not so presumptuous to say what's in your comfort zone and budget.  That said, based on your comments so far, I'd suggest something like this:

Suppose you have a so-called 2-input (a.k.a dual-coil) latching relay.  You trigger the "set" input of a latching relay and it closes its electrical contact.  The relay stays closed until it receives a trigger on the "reset" input.  So the basic idea to to set the latching relay when the train is about to enter the downgrade...and then reset the latching relay when the train exits the downgrade.  Latching relays as a component are just a couple bucks...but assembled with screw-terminals to eliminate soldering and such run maybe $10 or more. Example above is from Azatrax which carries a broad line of interesting and useful electrical doo-dads for model train applications.

The latching relay could be "set" and "reset" by a 10-cent magnet passing over a 50-cent reed switch.  I just made up the costs as I have lifetime supplies of these but it's one of those cases of you'll pay more for shipping!  There are pre-wired reed switches as these are very common in alarm systems to detect an open window or door.

As shown in the picture, you can embed the reed switch on one side of the track.  You can place the magnet on one side of the engine (or caboose or last car in consist).  By "one side" that means between the center-rail and either the left outer rail or the right outer rail.  You have to think about it for a moment, but that means if the consist is going the "other" direction, the magnet will not pass over the reed switch and the latching relay is never set/reset.

Note that I suggest this method as you apparently have only a few engines that would have to be out-fitted with the magnet.

Then, when the relay is set the reduced rheostat voltage would be swapped into the track center rail.  And when the relay is reset, the original "full" voltage would be restored to the track center rail.  If you are only operating 1 engine at a time, this full or reduced voltage could be applied to the entire loop and you would not need to fabricate isolated "blocks" with insulated pins and center-rail "islands".

Anyway, I see how this idea too is not simple plug-and-play.  But in the absence of other suggestions, if this is indeed something you'd like to pursue... or just discuss further in the spirit of a forum... I can elaborate.

No insult taken, Stan. You’ve got me pegged. As Adriatic suggested, I’m going to provide an outline of the layout, and an inventory of power supplies, locos, and accessories in an attachment (in a day or so) Then we can discuss your last post (and his - tho yours seems simpler and closer to my ability). 

(When this is complete I’ll be ready to return to the trolley discussion we put on hold last year, as well as the various ir doodads I’ve accumulated)

It almost seems a waste to let the 2 anti derail circuits in the loop fire, but not control something  else too.   

"How doesn't matter  much"

(What a great new photo. I'm grinnin' too 😁👍)