I have discovered a trick for changing a train's direction when you are stopped on a grade. Normally, after a timeout on a level spot, releaseing the key you are using for breaking (W or S) and pressing it again will cause you to change directions. On a grade, releasing the brake allows the train to move. You cannot get that pause. However, once you get to zero on a slope, use the space bar as a brake, after a short wait the above trick works.