That train will just keep coming. Once such a freight train is going you better get out of the way. The amount of kinetic energy that's coming towards you is dwarfing compared to a measly tank.
I don't think TNT is used at all, I'm pretty sure it's some explosive compound, as you said. However, explosives are still measured in terms of TNT, called Net Explosive Weight (NEW).
For example, one pound of C4 has a NEW of about 1.25 pounds.
Looks like it's something like 6-12kg of net explosive content so if that's the same as NEW then it seems that the train has it beat by a fair margin, though I doubt the trains impact is as tightly targeted.
I don't think your units make sense --- kinetic energy has units of energy, but "kg TNT per second" is power (about 4MW). (I think just remove the "every second" and it's correct?)
A large explosion every second has units of power, not energy. So to me this is suggesting that the train is putting out power equal to its kinetic energy per second. That's certainly not the case --- it implies that the train is powerful enough to accelerate to the speed in 1s, which is definitely not true.