system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why have motorcycle outriders in a motorcade?

From a security point of view, what advantage do they provide to a motorcade over some extra cars?
gpt
The motorcycles ride tandem and used to go ahead to block cross traffic. 

The pair up front blocks the cross traffic. The back pair move up to the front. And the blocking pair join back in the rear. 

4 bikes. 2 pairs. Continual moving traffic blockers.