As the object enters the first portal then the inertia of the far end of the object that is forced to pass through will need to be accelerated in the space outside the second portal to pass through, acceleration which is induced by being pushed by the other end of the object still outside the first portal.
In other words, pushing a portal onto an object pushes that object with half the speed of the portal. This will likely require energy put into the portal itself to maintain it, which needs to come from the train.
The train.
As the object enters the first portal then the inertia of the far end of the object that is forced to pass through will need to be accelerated in the space outside the second portal to pass through, acceleration which is induced by being pushed by the other end of the object still outside the first portal.
In other words, pushing a portal onto an object pushes that object with half the speed of the portal. This will likely require energy put into the portal itself to maintain it, which needs to come from the train.
That was an idea I’d floated above as well.
The train never touches the people.
The portal touches them first, moving where the people are.
The portal is moved by the train