Volvo VNL 780 Operator's Manual page 300

290 OPERATION
No Passenger Seat (Optional)
WARNING
Using a temporary passenger seating
without the benefit of proper seat
mounting and safety belt can, in the event
of a loss of control of the vehicle, cause
serious personal injury or death.
In vehicles with no passenger seat installed, DO NOT let a passenger ride on temporary
seating. This is against the law and can be very dangerous.