This report, the fourth in a series of four volumes produced on urban railroad relocation, describes the nature of the urban railroad location problem and estimates its magnitude nationwide. Costs of urban railroad/highway conflicts are estimated at 800 million dollars annually to highway users in delays and increased running costs, and 185 million dollars in accidents. Annual railroad costs are estimated at 75 to 100 million dollars for slowing and accelerating trains in urban areas and 70 million dollars for maintenance of grade crossing surfaces, marking, and warning devices.