Tractive Effort, and How Important It Is

[Saint Landwalker]

0% Important. None. Nada. Nil. (Edit: Refuted! With the nudging of @matrix47 and @grimdanfango below, further tests have been conducted. See Reply #6 for results.)

In the game, at least.

I ran a test wherein I created a "clone" of the D 1/3 locomotive, but instead of 15 KN of Tractive Effort, I gave it 150 KN of Tractive Effort. I then started a new Free Play using a perfectly-flat map, and bought one of each (the original, and the super-tractive clone, henceforth the STC).

I hooked up four D 1/3 Passenger Carriages to each locomotive, and sent them to the "starting line," a small two-lane passenger station. The course? A dead-straight, perfectly flat, roughly 1.5 km run to the "finish line" station.

At my signal, the trains took off! I mean, in as much as a D 1/3 can take off.

Well, if you thought having tenfold tractive effort was going to make an iota of difference in the realm of acceleration, you are going to be disappointed. Aside from a very slight delay between when they actually started, the trains ran a dead heat. Had their starts been properly synchronized, they would have tied perfectly.

"Curious!" thought I. But then, "Perhaps the game uses Tractive Effort for hill climbing?" So I deleted the original course, and replaced it with a steep, manually-created climb to the midpoint between the stations, and then a comparable descent to the other side.

Again, I set the trains loose.

Again, they performed perfectly identically.

Today's Lesson: You can completely ignore tractive effort when purchasing locomotives for any purpose.


(As an aside, multiplying Tractive Effort by 10 also has no effect whatsoever on the cost of the locomotive, so take solace in the silver lining that you aren't getting cheated at the checkout counter by buying high-TE locomotives. Cost of single-unit locomotives is only based on Top Speed and Power.)

[matrix47]

please, study physics first, then post "findings" like this.
as a start, try multiplying power of the locomotive by 10 instead of tractive effort. check the results. think.

[matrix47]

OK, I won't be so evil after all.
Think about tractive effort as if it was stickinness of your shoes. If it is 0 - then your shoes are basically made of ice. No matter how strong you are and how fast you are trying to run - you can't move (shoes are perfectly slippery).
If your shoes are sticky enough - good, you can move. But it doesn't make too much difference if you make your normal shoes 10 times stickier - you will still walk at the same speed! They will probably stop you much faster when you land at 200 km/h, but that is far from normal scenario.
Now, if you go to the gym and add some muscules to your legs, you can walk faster by pushing harder with your legs (If your shoes are sticky enough. I am sure those chinese Adibas can start to slip worn by Mr. Bolt). This is what you actually need to go faster - muscules. And vehicle's power stands for those muscules.

[Saint Landwalker]

Originally posted by matrix47:

please, study physics first, then post "findings" like this.
as a start, try multiplying power of the locomotive by 10 instead of tractive effort. check the results. think.

Clearly, trying to think is what got me into this situation to begin with.

[matrix47]

Originally posted by Landwalker04:

Originally posted by matrix47:

please, study physics first, then post "findings" like this.
as a start, try multiplying power of the locomotive by 10 instead of tractive effort. check the results. think.

Clearly, trying to think is what got me into this situation to begin with.

Hey, good for you! You were quite right to suspect that tractive effort was important on hills.
But 4 carriages is not enough weight to see the difference. Probably with 10 that would be noticeable.
So, in this game locomotive's tractive effort is more important for freight trains, because they tend to weigh much more than passenger ones. I am no expert in trains at all, but I suspect this also stands in real life.

[Dan]

Try hooking up more wagons... I'd guess tractive effort would have a pretty minor effect on a short train, on the flat. If you hook up 20 wagons, it should show what effect, if any, the value has.

[Saint Landwalker]

Originally posted by matrix47:

Originally posted by Landwalker04:

Clearly, trying to think is what got me into this situation to begin with.

Hey, good for you! You were quite right to suspect that tractive effort was important on hills.
But 4 carriages is not enough weight to see the difference. Probably with 10 that would be noticeable.
So, in this game locomotive's tractive effort is more important for freight trains, because they tend to weigh much more than passenger ones. I am no expert in trains at all, but I suspect this also stands in real life.

Sounds like another experiment is in order, then!

I ran the same test as the "Hill Test" from my original post, only this time each locomotive (the "15 KN Baseline" and the "150 KN Test Subject") had 20 cars instead of 4 cars--a total weight of 130 tons for each trains (as opposed to 50 tons in the original test).

Once again, the trains started off neck-and-neck. However, as they progressed up the climb and started losing speed, the 150 KN test train "bottomed out" at a speed of 5 km/h, while the 15 KN baseline train dropped down to 3 km/h.

Over the span of the climb (approximately 2 km), the test train crushed the control train. The test train reached the apex of the climb while the control train was roughly 60% up the hill.

Tractive Effort has value after all!

And there was much rejoicing.

(It still doesn't affect price, though, so congratulations to all hill-course-heavy-freight-haulers out there.)

[Dan]

Originally posted by Landwalker04:

(It still doesn't affect price, though, so congratulations to all hill-course-heavy-freight-haulers out there.)

Isn't the price just set specifically according to how the developers decided to balance things? It's not generated procedurally is it?

[Saint Landwalker]

Originally posted by grimdanfango:

Originally posted by Landwalker04:

(It still doesn't affect price, though, so congratulations to all hill-course-heavy-freight-haulers out there.)

Isn't the price just set specifically according to how the developers decided to balance things? It's not generated procedurally is it?

It's generated by some sort of hard-coded formula (unless you override it in the game files).

I don't know what the formula is -- that was the original problem I was trying to tackle before getting sidetracked by Tractive Effort. But I do know that, if you adjust vehicle statistics, the game's calculated cost changes.

I also know that for single-unit locomotives, at least, the only variables that affect that calculation are Power (KW) and Top Speed (km/h). The effect of Power is very straightforward, but the effect of Top Speed has been impossible to decipher.

[Aries]

Launched these 2 at the same time, 1x emd on track 2, 2x emd on track 4 http://steamcommunity.com/sharedfiles/filedetails/?id=803687601

After 1 lap, 1x emd is way back there where the cursor is highlighting it http://steamcommunity.com/sharedfiles/filedetails/?id=803687708
So better lap time for 2x emd's is due to having more combined hp and kn or that they have more hp.. Also a nub question, where does it say the length of the track: "Over the span of the climb (approximately 2 km),"? how would u know its approx 2km? just the mk1 eyeballing it?

Yes Grim, its generated based on few factors, speed, hp.. increase capacity/top speed for a wagon/bus/plane and the price and upkeep will be higher

[Saint Landwalker]

Originally posted by Aries:

Also a nub question, where does it say the length of the track: "Over the span of the climb (approximately 2 km),"? how would u know its approx 2km? just the mk1 eyeballing it?

Pretty much. I knew I was using a 4-km by 4-km map, so I could eyeball that the incline I was using as the test track covered about half the width of the map.

[Aries]

Originally posted by Landwalker04:

about half the width of the map

That's some smart sht right there:)

[SirLANsalot]

On a flat map, yes Tractive Effort means nada, however we do not play with flat maps, unless intentionally using one. Tractive effort is VERY important to normal game-play, as (you have seen with your test) it means how many cars your locomotive can use before slowing down going up a hill (ANY HILL).

Combining locomotives does properly combine there HP and Tractive Effort, so they can pull more cars, with less of a slowdown (like the ALCO HH is a great little loco for that purpose).

[sponsz]

Tractive effort is the maximum force an engine is able to transmit onto the track. Basically, the formula is "force = min(power / speed, tractiveEffort)". In other words, up to a speed of "power / tractiveEffort", the force (hence acceleration) is limited by tractive effort, and above it is limited by power. In your example with the D 1/3, we get 50.0 / 15.0 = 3.333 m/s => 12 km/h for this threshold speed. So if you increase the tractive effort from 15 to 150, you will only see a difference between 0 and 12 km/h (because above 12 km/h, power is the limiting factor).

To summarize, tractive effort only has an influence at low speeds (when the vehicle starts); and that's why it is not included in the price / running costs formula. Hope this helps :-)

[GeneralGeldenhuys]

Basically, tractive effort is like the locomotives grip and will play an important role on steep sloped tracks. The longer the train, the slower it will go up the hill and if you exceed the trains weight against the tractive effort, the train will slip. In the game, however, the trains doesn't slip and they have a minimum speed, regardless how heavy it is.

What do means a LOT, is the amount of KW (horsepower) the locomotive can push out. Tractive effort will determine the acceleration (there is a maximum acceleration/deceleration) while KW determine speed.

When you attach 2 loco's at the front, you double the KW and thus a train can go faster up a hill.

It looks something like this for a 7MW locomotive.
https://en.wikipedia.org/wiki/Tractive_force#/media/File:Schematic_tractive_effort_curve.JPG

Point A and B is a limiting factor of the wheels on the rails. B to C is the reduction of tractive effort due to the limitation of only having 7MW available. As train increases in speed, so does the tractive effort reduces and therefore the train cannot reach top speed on slope tracks.

[LennZ]

Originally posted by sponsz:

Tractive effort is the maximum force an engine is able to transmit onto the track. Basically, the formula is "force = min(power / speed, tractiveEffort)". In other words, up to a speed of "power / tractiveEffort", the force (hence acceleration) is limited by tractive effort, and above it is limited by power. In your example with the D 1/3, we get 50.0 / 15.0 = 3.333 m/s => 12 km/h for this threshold speed. So if you increase the tractive effort from 15 to 150, you will only see a difference between 0 and 12 km/h (because above 12 km/h, power is the limiting factor).

You should take a good look at your code, because that's not how it works in game :P

I tried to find out how it all works, the results are in these reddit threads:

https://www.reddit.com/r/TransportFever/comments/5dm6ej/short_analysis_of_train_physics/
https://www.reddit.com/r/TransportFever/comments/5e3jme/the_impact_of_of_tractive_effort_on_slopes/

Rather than following the formula you described, it's following something more like this:

f=min(max(ft, P/2v)), P/v)

Meaning that the tractive effort is ignored at low speed, which explains why train acceleration out of the station is so damn high. Furthermore, in my tests there was absolutely no impact of tractive effort on the terminal velocity on hills, only the rate at which they accelerate / slow down when going uphill.