In addition to seatbelt requirements and child safety seat laws, Colorado also has laws pertaining to passengers outside the vehicle interior. This article explains when a passenger or pet can ride in the bed of a pickup truck and the penalties for a violation.
Colorado's seatbelt law requires all front-seat passengers and children under 16 years old to be properly restrained. Colorado law also prohibits passengers from riding on the hood, on the fenders, or in any non-enclosed portion of the vehicle. However, passengers are allowed to ride in a sitting position in the cargo area if enclosed on all four sides. In other words, seated passengers who are at least 16 years old can ride in a pickup truck bed (with the tailgate closed) in Colorado. (Additional exceptions exist for parades.)
Violations of these requirements are class A traffic infractions for the driver. A conviction carries a $65 fine and $16 surcharge.
While restrictions exist for human passengers in the bed of a pickup truck, Colorado doesn't have similar laws that apply to pets or other animal passengers. However, the American Veterinary Medical Association recommends that pets be secured either by a kennel in the truck bed or by a harness inside the cab.