He might also interpret his experience thus: “My body of reference (the carriage) remains permanently at rest. With reference to it, however, there exists (during the period of application of the brakes) a gravitational field which is directed forwards and which is variable with respect to time. Under the influence of this field, the embankment together with the earth move non-uniformly in such a manner that their original velocity in the backward direction is continuously reduced.”
Opposing gravitational forces in their own referential frame.
