Should the U.S. raise terror alert, like the U.K.?

(CNN) – According to AAA, 35 million Americans will be traveling this labor day weekend, the highest number in six years.

So pack the kids in the car, board a flight, or take a seat on the train - and don't worry too much about ISIS terrorists committing an atrocity on U.S. soil, according to the FBI and Department of Homeland Security, who are unaware of "any specific, credible threat to the U.S. homeland" from ISIS.

This, despite the British government raising the alarm about ISIS within its own borders.

On this holiday weekend, why is London so worried, and Washington not?

CNN's Barbara Starr reports.