These guys have a website that sells train horns for your car. theyre huge!!!!! and they are very loud. These are some of their videos they made raising hell with the horns
here is a link to more vids on their site. pretty much the whole left side is them messing with people. make sure to watch the first "jesus saves" one at the top left. that one is hilarious.
you can also buy the horns from that site. enjoy.....