Locking roller assemblies for locking and unlocking a roller of a roller conveyor. The disclosed locking roller assemblies include rollers that, by default, are locked from rotation in the absence of a transferred object such as a container, crate, or pallet. When an object is present over the roller, the roller is passively actuated by the object to unlock and release the roller, enabling the roller to rotate. When the package or article has passed by the roller, the locking roller assembly resumes the default configuration of locking the roller to prevent rotation. In some embodiments, actuation of the locking mechanism is parallel to the roller axis and accomplished by a lever and cam arrangement. In other embodiments, actuation of the locking mechanism is in a direction that is orthogonal to the roller axis and accomplished by a plunger arrangement.