RTG stands for Rubber Tired Gantry Crane - a portside device used to move and load the containers onto and off of ships. They don't get a lot of horizontal mileage but the crane racks up plenty of miles vertically. Raising a container is the equivalent of accelerating, increasing potential energy, and lowering the container is like braking, providing an opportunity for regeneration.
Railpower is a firm that I last knew made diesel-electric hybrid railroad yard locomotives. This is an equivalent and brilliant way to save fuel with relatively little changes. Both locomotives and RTG cranes have diesel electric drive systems and there is plenty of room and capacity for a decent sized battery pack.
How much is saved on the Hybrid RTG? Quiet a bit actually, in typical activity. As reported, the diesel/battery hybrid power plant achieved 74 percent fuel savings. An average of 70 percent of the energy lifting a container can be regenerated when lowering it. The hybrid's fuel burn rate during active typical duty cycles was 2.08 gals/hr. Conventional RTG cranes run at about 8 gals/hr.
This seems to be an excellent application of hybrid technology, peak oil or no peak oil.[Source: Railpower]