Say guys & gals; following up on warning devices that put the true meaning of fear back into cluless drivers someone today reminded me of something I haven't thought about in years. Remember coasting up to a light, turning off they, waiting a couple seconds and then turning thekey back on KA-BOOM a backfire that shook windows. How about a propane cannon?
Piece of pipe with a weighted hinged cap with a o-ring for a slight seal that would let a little gas build up and a source of ignition; might produce really pleasing results.