53-d. Unlawful propulsion of a missile at railroad trains. A person is guilty of unlawful propulsion of a missile at a railroad train where he willfully with intent to cause personal injury or property damage throws, shoots or propels a rock, stone, brick, or piece of iron, steel or other metal or any deadly or dangerous missile or fire bomb at any locomotive or car of a train which is occupied by any person or persons. Unlawful propulsion of a missile at a railroad train is a violation; provided, however, that such classification shall not apply in any case where an offense having a higher classification for the purpose of sentence, is charged under any other provision of law.