At which of the following must a bus driver still slow down and carefully check for traffic, but is NOT required to come to a full stop?

49 CFR 383.117(a)(4), Proper procedures at railroad-highway grade crossings and drawbridges

Stopping unnecessarily at a controlled crossing can create rear-end crash risk and traffic backups, while stopping only when actually required keeps traffic flowing without sacrificing safety at crossings that have no other active control.