A common idiom in the U.S.A. is “riding shotgun”. This means to ride in the front passenger seat of a vehicle. This idiom comes from the old American west.
The picture above shows an old stagecoach. One person would have to drive the team of horses. The other person in the passenger seat would hold a powerful gun called a shotgun. The person “riding shotgun” would protect the people or cargo inside the stagecoach.