Have you ever noticed those diamond shaped placards on passing trucks? The ones with the four-digit numbers? They identify the contents so that responders to an accident know right away whether to put on bunny suits and evacuate nearby towns or just mop up the mess.
Now you can know, too. When you enter a valid ID number, you get a list of the possible payloads.
This is only applicable to US trucks. The data comes from the US Dept. of Transportation's Emergency Response Guidebook. Requires Internet access.