NO x , which contribute to acid rain, also have a minor role in stratospheric ozone depletion when they are released high up in the atmosphere by airplanes. A well organized and efficient transportation can reduce the number of empty seats on any type of vehicle, reducing the energy consumed per person per trip. Freight Transportation Anybody who has travelled on the highways in North America has seen that a large proportion of our freight is transported by heavy trucks. This was not always the case. Before freeways and improvements to diesel engines, trucks were not a major carrier of long distance freight.
Railways criss-crossed the continent, with tracks leading to virtually every town and every factory.
This is unfortunate from an energy perspective, because as shown in Figure 3, trains are about 4 times more efficient than trucks. Today, railways are predominantly used for moving raw materials such as ore and grain, and account for about one third of tonne-kilometers travelled. Figure 3 shows that pipelines are the most efficient mode of freight transportation. For years, pipelines have been used to transport oil. Water based transportation is a very efficient method of moving freight, which has been used by mankind for thousands of years, wherever possible, from ocean-going sailing ships, to the canoes of the voyageurs.