A rider becomes drunk and disruptive partway through the route. According to the manual, whose safety must the driver ensure?

49 CFR 383.117(a)(3), proper responses to emergency situations such as fires and unruly passengers; AAMVA CDL Manual Section 4.3.2 (p.4-3)

This is one of the six topics every Passenger-endorsement applicant is federally required to be tested on. Understanding that the duty of care covers the disruptive rider too, not just other passengers, prevents drivers from making an unsafe decision like putting someone out in a dangerous spot.