I know you're joking, but I'll take you seriously anyway. Using a magnet could actually make things worse. There will be some mass that the magnet can lift fa

I know you're joking, but I'll take you seriously anyway. Using a magnet could actually make things worse. There will be some mass that the magnet can lift fast enough to clear a path, but over that mass it will only partly lift objects. There's a good chance it will partly lift objects in this mass range and cause them to stand up whereas previously they would have laid flat and just been driven over. Yeah, I know, just use a much bigger magnet. Should be interesting at a railway crossing.