But, as author Tom Vanderbilt pointed out in his book "Traffic: Why We Drive the Way We Do," Grohol said people slow down when they see people or feel uncertain. Taking their cue from that observation, engineers put up silhouettes of people to change drivers' behavior.
"Novel situations really do get people to slow down," he said, adding that similarly security warnings need to continually come across as unexpected and unique in both the message and the medium.
He acknowledged that Internet and national security may be more challenging, but said the key is to be adaptive and creative.
"[Successful messages] are always changing in order to continue to get people's attention," he said.