Bridge travel in crane operation is defined as movement:

Bridge travel in crane operation refers to the movement of the crane's bridge along the runway, which is designed to provide horizontal movement across the vertical plane of the operation. This type of travel is essential for positioning the crane’s hoisting mechanism over the load it needs to lift or move.

By moving parallel to the crane runway, the bridge allows the operator to cover the required distance and accurately place loads where they are needed. Understanding this movement is crucial for the safe and effective operation of cranes, as it relates to load handling and overall efficiency in lifting operations.

In contrast, the other options describe movements that do not align with the operational definition of bridge travel. For instance, movements that are perpendicular, solely upward and downward, or confined to the vertical axis do not accurately represent the bridge's functionality within the crane's operational envelope. This understanding is fundamental for operators working with cranes, particularly in ensuring that they can navigate and utilize the equipment correctly and safety.