Did this painting today in photoshop. Used ref for the background. I accidently saved it as the psd rather than a jpeg so there is no going back which is unfortunate as i was only messing about with the motion blur.
You need to add blur to the background also to give it a sense of speed. If only the ship is blurred, the concept of motion is lost. Also, the ship isn't up to par with the rest of the rendered detail, like the trees, grass. Did you just superimpose this on top of a photograph and then paintover it?
I would actually remove the blur from the distant mountain range, but leave the blur on the grass, and to a lesser extent on the trees. Not sure about the vehicle. It all depends on the motion of the camera/observer. If you're moving with the vehicle then there should be no blur on the vehicle. Motion blur should be absent from the mountains because they are practically an infinite distance from the camera. I notice a bluish haze in front of the mountains, which is good because it makes them look like the intervening atmosphere is scattering light.
Perhaps the observer is moving rapidly with respect to the grass, but not quite as fast as the vehicle, although maybe that results in a more complicated image than you want.