I assume https://www.youtube.com/watch?v=R0LCmStIw9E is the one you are thinking of (there was a shorter version that aired in TV ad breaks).

The Think! campaign was always pretty on-the-nose, as you need to be sometimes to get these messages across. The seatbelt and in-town speed limit ones stick in the mind too: https://www.youtube.com/watch?v=mKHY69AFstE and https://www.youtube.com/watch?v=jDpOAXfangI respectively.

The memorably stark tone and the frequency they were on TV made these spots ripe for parody, for example this one from Monkey Dust: https://www.youtube.com/watch?v=PsOk9Ln1qOY