The car takes about one second to get from the beginning to the end. This movie plays at 12 frames per second (fps). To make the car move more slowly, we need more frames. You could click and drag the keyframes to a later point on the timeline. This will stretch out the length of the animation, but it will still be jumpy.
To make it less jumpy, you need not just more frames but more keyframes. This would allow the car to move less each time, giving the illusion of a smooth transition.