Since World War II, soil compaction problems have spread from the southeastern states to include most of the country to some degree. Subsoil compaction has increased as equipment size increased. Research has shown that subsoil compaction is primarily a function of total load on the traction device. Research has also shown the importance of the shape of the traction device for traction, flotation, or soil compaction. Another principle of soil machine relations is the critical reaction of a tilled soil to the first pass of a tire. Efforts which were begun to eliminate soil compaction have been expanded to completely manage traffic-induced soil compaction. Soil compaction can be very detrimental in the root zone and very beneficial in the traffic lane. Controlled traffic is a compaction management concept that can provide the conditions desired for crop production systems.