This is hard to describe without being pedantic and without being able to draw but I will attempt. A motorcycle performing a stoppie experiences rotation becau

This is hard to describe without being pedantic and without being able to draw but I will attempt. A motorcycle performing a stoppie experiences rotation because the inertial force couples with the braking force to create a moment about the front axle of the bike (this isn't technically correct language but you get the gist). While this idea holds true for the train, we have to take into account the differences in mass and contact between the two systems. Train cars typically ride on more than 2 axles and this provides stability from front or rear tipping. Train cars are also typically very heavy meaning that the braking force is not sufficient to 1) move the center of forces of the system ahead of the front axles and 2) tip the car. Increases in load because of this are, therefore, not sufficient to double the load on the front axle as you would see with a stoppie. In general I agree with the idea that is put forth; however, it is important to note that what we are discussing is the BRAKING force. The inertial forces that result in differential axle loads is not a braking force (certainly, it is a result of braking in this case but this force also exists when a train begins pulling). These loads are DYNAMIC loads and are already considered in another part of the analysis. Dynamic loads also include consideration for bumps, etc. Because of this, the code is explicit that braking forces are applied only longitudinal to the track so that the forces are not counted twice.