Beta test the new forum at
Want to praise Simutrans?
Your feedback is important for us ;D.

Standard Vehicle Power - Calculations

Started by Guy the Wise, July 28, 2021, 10:24:37 PM

Previous topic - Next topic

0 Members and 2 Guests are viewing this topic.

Guy the Wise

I've got an addon pakset that I want to modify for private use. I've noticed that some steam engines are underpowered as all heck (3 passenger cars before max speed starts dropping), whereas some of them are absolutely OP (15, 20 cars before max speed starts dropping). I understand that power is measured in kilowatts and I can modify power output and other variables to my heart's contents thanks to having the source files, but I'm unsure as to how to calculate power output. I should be able to use for numbers thanks to them listing multiple different stats and the pakset containing real locomotives. If only I could just plug those numbers straight into the .dat file....
Does anyone happen to know how to take these numbers (tractive effort, cylinder dimensions, factor of adhesion, etc.) and convert them into numbers Simutrans Standard can use?


It is impossible.

First reason is that standard does not use real physics but deliberately something close to looking good in relation to reality.

Second reason is that steam engines work very different than like diesel or electric engines. Steam engine deliver their full power only at slow speeds and then their power drops (due to various issues, like drag in lines, cyclinder exchanges, and boiler evaporation ares, or however this is called in English). Electric engines have essentially the same power at all speeds, and diesel are somewhat underpowered when starting.

Hence there is a peak power you can get of cylinder diameter times operating pressure (essentially the tractive effort). But this is way higher than the actual cruising power, which is usually limited by the boiler. There is no easy way to convert these two.

In pak64, you can find in vehicles "cars.xls" Go to the second tab "Tabelle2". Here enter vmax for your criusing speed and the weight of the train including engine and adjust gear and power until your realistic results.

The engines in pak64 have been adjusted this way using their max speed, which is not when they usually have operated. Hence, if there are slower cars, the engines will pull more of them. (Around 1900 the typical speed of a steam train was around 55 km/h and express trains rarely went of 80 km/h on average. Simutrans greatly exaggerates the speeds.)

ANyway, whatever pakset you a looking at, I think people will be interested if your share your results.

Guy the Wise

I thought it was that steam developed power as they got faster.
If memory serves me right, steam HP increases as speed increases until it reaches a certain point, then starts tapering off as the boiler becomes unable to keep up with steam consumption. Constant torque (tractive effort?), variable power. Diesel and electric, on the other hand, are the opposite: constant power (HP/kW), variable torque, losing the ability to accelerate a train as it gets faster.

I understand the concept of slower cars on faster engines, but they still kinda seem underpowered. For instance, JGR 8620's (one of the addon engines I'm trying to modify) may pull about 3 cars in the preservation era (modern day), but that's not much to say about its full capabilities as supposedly demonstrated during their revenue service days. In-game, the statistics seem to support it's in-preservation abilities: 85kph (limited by cars; max engine speed is 90), 179t empty, 197t loaded with 240 passengers. Meanwhile, I can have a C56 (branchline engine; 75kph top speed) lead and sacrifice 10kph in order to be able to move 320 more passengers (560 passengers, 290t empty, 332t full). The C50 doesn't fare any better than the 8620, losing only 2kph fully loaded with a fourth car as compared to the 8620 losing 1kph empty and going down to 78 full. Unfortunately, I haven't been able to find anything at all as a benchmark for either engine's real-world performance.

I have managed to find different formulas for horsepower computation, but because steam engines are complex (as you said), the formulas can be misleading unless it's denoted for at the cylinder, drawbar, boiler, etc.
As well, I've only been able to find one online article denoting the same engine's theoretical power in kW, however I haven't been able to figure out how that number was derived.

On average train speed, it seems to vary a bit depending not only by year, but by region/country as well. Rail infrastructure varies rather wildly from country to country. Freight trains here in the States around the 1900's, 1910's would usually hit 50mph, roughly translating to 80kph.

Thanks for the support though; I hope I can figure things out without losing my mind. I may just have to ballpark the numbers.


You are right, steam has constant force until the boiler does not generate the pressure any more, my fault.

Freigth train speed in Germany was 45 kph until well after world war one, since many cars did not even had a brake (in 1922 freight train brakes were standardized). Same for many other countries.

In the US the current limit of most track is 60 mph it seems, and empty trains usually go rather 40-50 mph. 50 mph in 1900 seems too fast for me, given the then avaiilable signalling and state of tracks and the cost of coal. Also most freight trains had no automatic brakes until it became mandatory in 1900 (according to The same source said "a test train travelling between 30 and 40 mph ..." (1885 or 1886)

I would be interested to learn more, as I found very little of information of freight speed in this early age.

But indeed in the 1920s and 30s it seems like freight was miving up to 60 mph on level tracks in larger part of the network. Do you have a reference for this fast early speeds?

Guy the Wise

Depending on where you're looking at, modern postage usually says either 60 or 79. Some companies effectively only allow intermodals to hit 79, something about only intermodals being allowed to go up to Run 8 (full power). Not sure who does that though. The reason behind 79mph as top line speed is that the Interstate Commerce Commission in 1947 ruled that trains and accompanying track must be fitted with both any form of automatic train stop (think Britain's TPWS) and in-cab signaling (just shows the aspect of the next signal) before speeds of 80mph and up can be attained. I imagine this is part of why American railroading in general took a dip in the 60's, along with the Eisenhower System.

Brakes weren't entirely mandated per se, but the first Railroad Safety Appliance Act (1893) pretty much did outright mandate not only train braking, but a form of automatic car coupling as well for interchange traffic, with a grace period of 5 to 7 years for the railroads to conform to it. Railroads at the time were still using link & pin, which seems to be a derivative of link & hook. This system has a socket, aka "pocket", on either end of the car or a reach bar on the front if it's a locomotive in order to clear the cowcatcher. A worker insert a single chain link into one of the sockets, secure it with a pin, and walked with the the link in hand as the consist backed up until the link goes into the other car's socket. As one can imagine, there were quite a few appendages that went missing....
The act was a little vague, so it got updated in 1903 with the Second Safety Appliance Act to state that:
a. All vehicles operating over interstate commerce highways ( within the scope of the Safety Appliance Act.
b. At least 50% the train's consist must have train brakes.
c. The ICC has authority to increase the above ratio if it were deemed necessary.
The 1910 Act didn't do much except for strengthening provisions and mandating extra safety appliances (ladders, hand brakes, sill steps, etc.), along with exempting certain conditions.
It's certainly true that the ICC at least gave the industry a push to adopt car braking; I believe the 1889 report stated less than 8% were equipped with train braking?
(; pages 7-11)

Unfortunately, there really isn't much data at all on freight train speeds until more modern times, say some time between the 1910's and 1950's. I've only been able to garner info from secondary sources, namely in some Discord servers I'm part of. Even then, different railroads allowed different top freight speeds, usually ranging anywhere between 40 & 60. After reading through the available material, including what you sourced, I'm willing to drop average 1900's loaded speed down to between 35 & 45mph. I imagine the only freight trains around that time that really got up to 40, 45, 50 if that ever happened, were merchandise trains (consumer goods). They certainly did speed up afterwards though; some trains even got exceptions to run at faster speeds. I believe it was around the 40's-50's when the Cotton Belt Route (Southern Pacific subsidiary) started forcing allowing their Blue Streak Merchandise to hit passenger speeds (70, 80). In order to keep in mind how truly impressive that is, it's worth to note that the BSM used regular equipment. No roller bearings, no fancy gadgets. Just straight-up boxes, flats, etc. between St. Louis & Los Angeles with a flying crew change in West Colton, CA.


I found that in the mid 1930 BigBoy and related engines were built to sustain 60 mph even for freight. Wikipedia states too that 80% of the rails are only rated class 4 i.e. for up to max 60 mph for freight in the US. So I would guess freight speed went from 30-49mph around 1900 to 60 mph in the 1930ies.

Otherwise there is the citation from back to future that the steam engine there ususally cruises at 25 mph with a top speed of fifty ...


I think the vehicles in Simutrans must be considered somewhat symbolic. A modern European freight train with a single locomotive seems to easily have more than 20 cars. In pak64, such a train will no longer be able to reach top speed, except downhill. That typically means you lose a lot of speed bonus, more so because speed bonus for trains are very high due to much faster passenger trains. Furthermore, the will accelerate so badly, that everything slows down. And there is no such thing as a gentle incline in Simutrans. It may be short, but it has full steepness. Forget about sharing lines with passenger trains, which still is rather common in Norway at least. Maybe a powerfull passenger locomotive could pull more freight at realistic speeds, but the cost in Simutrans would be too high for freight, because the cost is meant to balance the higher speed bonus for passengers.

In addition, a train with a realistic number of cars will dwarf pretty much anything else. Back when most pak sets were made, maps were much smaller than one seems common today. Such a long train could easily be more than one percent of the map size, and might often enter the next town before fully leaving the previous.


The length of a central European train is limited to 740m (although this is slightly increasing, as it was rather 500m 50 years ago), so assuming a mean length of 25 meters would allow 27 cars. (Actually, when I was still living in Germany ten years ago, most trains I counted during daytime had less, typical around 15 cars.)


I just found a video on YouTube with some German freight trains. I counted the first two trains, which were both container trains. I counted over 20 cars on both. The first seemed to have only cars carrying one 20 ft container, the second had a mix of that and cars that carried two containers.

With pak64, I find that 7 or 8 cars seems to be how many contemporary cars a locomotive can pull. That seems to be the general length where income starts covering locomotive running costs as well.

I have trouble finding information about how long trains were fifty years ago or more. A measured a couple of passing loops in Norway on Google Maps, that old photos show haven't changed in fifty years, and they are about 350 to 500 meters. However, cars have become longer with time, and they do in pak64 as well. Locomotive length did however probably peek mid 20th century with the last steam locomotives, if we count more or less permanently couple things like IORE as multiple locomotives, and not as a single one.


The trains I counted were never container trains (there were not passing where I lived), but mostly oil trains. Since Oil is much heavier than containers, maybe that is why those tend to be shorter.

Until at least 1955 the legal length in West-Germany was 150 axles (or 100 for speed above 45 km/h per hour), which would result in a limit of 25 cars for 80 km/h.

In case of Simutrans also the proportions are skewed, so a 8 car train is 4 km long ...


Quote from: prissi on August 05, 2021, 02:25:46 AMIn case of Simutrans also the proportions are skewed, so a 8 car train is 4 km long ...

Which also shows that things in Simutrans are symbolic. Towns also have far fewer buildings than they should for a given population.

And considering the time a vehicle uses to complete its schedule, it is not only symbolic spatially, but also symbolically. If vehicles were to literally represent a realistic vehicle, they would either have to move so fast it would be a blur, or time would have to slow down to real time. That the game has a fast-forward button, suggest that even the accelerated time in Simutrans is sometimes considered too slow for some.

Most games, on the computer or otherwise, deviate from realism. What matters is that they are internally consistent. Not that Simutrans is perfect in that regard, but adding full realism in one (small) aspect may actually make things worse, by lowering that consistency. At least in the short run.


Freigth train speed in Germany was 45 kph until well after world war one, since many cars did not even had a brake (in 1922 freight train brakes were standardized). Same for many other countries. 


The length of a central European train is limited to 740m

that isnt true..

Isaac Eiland-Hall

Quote from: spiceagent11 on May 25, 2022, 01:02:20 AMthat isnt true..

Feel free to provide a source.

Meanwhile, I have removed the spam links from your profile. Do not re-add them or you will be banned.


Quote from: spiceagent11 on May 25, 2022, 01:02:20 AMThe length of a central European train is limited to 740m

that isnt true..
740m isn't a really hard limit. Longer trains are sometimes allowed, but they are severely limited in where they can go. Just a handful of routes allow trains of 1000m.