The direct utilization of minimally processed solid fuels (particularly coal) in transportation engines is assessed. Both highway and non-highway applications are considered. In general, solid fuels do not seem appropriate for highway transportation in the 1980-2000 time frame. Such fuels can be utilized for non-highway transportation with some engine types. Both technical and environmental issues are explored and a systems approach for studying the topical area is stressed. The paper features a brief historic review and current update on activities in the area of direct solid fuels utilization in transportation engines.