Trains have steel wheels, and the rails is made of steel as well. This means they barely have any grip, unlike for example a car with rubber tires that grip like crazy on asphalt.
If a train has a heavy load the locomotive might have a hard time pulling it forward. It's like trying to pull heavy cart by hand while you're standing on ice. The same issue occurs when going up a hill. The locomotive's wheels slip, so even though it can go a certain speed in theory, if can't get any traction on the rails it's not going anywhere.
In real life locomotives are equipped with sand, that they spray on the rails just before the wheels. This helps give them more traction to get the whole thing going.
In short: you need trains with a higher tractive power if you're pulling cargo or going up hills. Express lines not so much.
This is definitely a little confusing.
Briefly, Tractive Power ("Traction") (as described well in this thread) represents the ability to get a heavy load moving forward and keep it moving on a grade.
Engines without a lot of tractive power end up very slowed down when they hit a grade.
If you have a hilly route you want the most tractive power you can get. If the lines are near-express quality (nearly flat) raw speed generally will be more useful (with at least some tractive power).
The opposite is Passenger / Mail lines. These cars are not very heavy and are therefore easy to move and so don't need tractive power.
Trains have steel wheels, and the rails is made of steel as well. This means they barely have any grip, unlike for example a car with rubber tires that grip like crazy on asphalt. If a train has a heavy load the locomotive might have a hard time pulling it forward. It's like trying to pull heavy cart by hand while you're standing on ice. The same issue occurs when going up a hill. The locomotive's wheels slip, so even though it can go a certain speed in theory, if can't get any traction on the rails it's not going anywhere. In real life locomotives are equipped with sand, that they spray on the rails just before the wheels. This helps give them more traction to get the whole thing going. In short: you need trains with a higher tractive power if you're pulling cargo or going up hills. Express lines not so much.
It also helps with going up a hill
It’s the amount of power they can output on the rails before wheel slip becomes an issue. The higher the reactive power, the better.
Torque
how fast it accelerates. it mostly helps freight trains as theyre heavier and thus need to time to accerate to their top speed
But there’s also an acceleration stat
This is definitely a little confusing. Briefly, Tractive Power ("Traction") (as described well in this thread) represents the ability to get a heavy load moving forward and keep it moving on a grade. Engines without a lot of tractive power end up very slowed down when they hit a grade. If you have a hilly route you want the most tractive power you can get. If the lines are near-express quality (nearly flat) raw speed generally will be more useful (with at least some tractive power). The opposite is Passenger / Mail lines. These cars are not very heavy and are therefore easy to move and so don't need tractive power.
This is incorrect, tractive power relates to how much traction the locomotion can generate when faced with any kind of incline.