Which of the following is NOT characteristic of heavy grade operations?

In the context of heavy grade operations, the characteristic of having a distance of less than 3 miles is indeed not representative of these types of operations. Heavy grade operations typically occur on grades that require more significant management and control of the train, particularly when traversing steep inclines or declines. The distance of less than 3 miles does not align with the expectations for heavy grade operations, which often involve longer stretches of sustained grades.

Heavy grades are usually characterized by rising elevation and being at least 1% grade, which presents additional challenges to train control, such as the need for increased braking and meticulous speed management. Therefore, while the other options reflect the true nature of heavy grade operations, the specification of a distance of less than 3 miles is a unique criterion that does not fit within this operational context.