Setting prototypical speed limits.


Active member
I found out it is not practical to set a 50 MPH zone using a speed limit sign through one or more turnouts in the mainline.

I have a situation on my latest model layout development where a JR signal will reveal a limited approach light setting (something like a yellow over green) if there are two turnouts spaced 1,300 feet apart in the mainline ahead whether the line ahead is perfectly clear and both main switches are set to green. It certainly will not allow AI to run at 50 mph on this approach. The signal immediately following the yellow over green will be something like a red/yellow light combination. I am now beginning to understand that part of the purpose of RR signals is to regulate train speed and not just warn drivers of danger ahead. The fixed speed limit signs alone are not adequate for safe train procedure as they are for cars on the highway.

Would 25 mph be a more realistic speed limit for approaching this pair of close turnouts? Any one of these switches could be suddenly thrown by another train at any time.

I want to set my mainline speeds based upon how far a human driver could actually see a signal ahead in perfectly clear weather conditions and not how far AI or the HUD display can see ahead.

I have a number of turnouts all around my figure 8 mainline (about 3.50 miles in the loop) where I don't feel there could be any 50 mph zone as I don't have any long-enough stretch anywhere on the line to make this prototypical.

Since this mainline is full of sidings and curve radii as tight as 250 feet in some parts, it will probably be a line for slow trains only.

I don't want to run a model layout like some hobbyists who have turns too tight and run trains at stupid high speed through them. I am designing my layout with real-world physics in mind.

It now seems reasonable to me that real American roads, by its speed-rules convention, would not permit 50-mph train speeds except in long stretches of mainline with no turnouts anywhere close ahead.
On a figure-eight type route, you'll never achieve an all clear. Your train by its very nature of being on the track in front of its self is setting the following signals yellow, therefore, the reason is your AI train sees its "caboose" in front of it, which to the AI means there's another train ahead, and in the real world means you need to operate at one half speed through the restricting signals.

If your route was a point to point, with occasional passing sidings/loops, then what you expect to happen will happen.

As far as prototypical speeds go, the sharpest curves will determine your fastest speed so plan your curves to be slower. This will have a cascading affect because on a loop layout, the AI are always slowing down in preparation for the slower speed ahead. The reason is pure physics due to the train needing to be at a slower speed in order to negotiate the curve - think about those recent nasty Amtrak accidents where the drivers did not slow down ahead of time and hit the curves at the high speed. In Trainz our AI are "smart" drivers that follow the rules and will start slowing down in advance of a slower speed.

So in the end, even if your mainline speed is 50 mph, or 100 mph, you'll never achieve this speed because:

1) The AI sees its self and runs under restrictions all the way.
2) The AI prepares to slow down for the upcoming slower speeds on the curves.
Thanks, John.

The only way I could practically achieve 50 mph, with a heavy freight, on a figure eight is if it were big enough, perhaps 10 scale miles or longer for a complete lap, with several miles of stretch, straight line track and/or broad curves, with absolutely no turnouts. If there are enough intermittent-placed signals and no turnouts, AI will in fact see GREEN down the track for a piece. One can also observe upcoming signal conditions by monitoring the HUD. In the real-world, human eyes in the cab of the engine can only see a lit signal but so far down the track unless they were to have modern electronic equipment in locomotives that could give the status of several signals down the line. Perhaps, dispatchers would radio engineers or train conductors of approaching trains if warnings of known track hazards ahead were needed to be given.

There is a portion of my smaller figure eight where a lighter, shorter thus faster-accelerating passenger train could briefly hit 50 mph once it clears the last turnout and associated signal for about 1.50 miles of no-turnout track but it would have to start slowing down again about 1 mile past the last turnout for a sharper curve that miles ahead. My half-mile-long freight would be lucky to even hit 35 on this layout.

Depending upon where the signals and turnouts are located, and how far they are spaced, one or more signals may in fact be green, clear, and AI may drive accordingly.

If I were to have my 3.50 mile figure eight with absolutely no turnouts, and perhaps three or more signals spaced evenly around, the signals ahead would stay green, clear, consistently if there were only one train running on the line. I know this by test-running trains on my layout as it continues to develop.
I prefer slow speeds of 1-5 mph, an a top speed of 25 mph, cuz' I'm a tad "Slow", an' rode the "Short Bus" till I was 17, in the 10th grade