After initial widespread use of private cars under the “common road” concept of early railways, railroad-owned freight cars predominated from the 1840's through the 1860's, except for a short-lived boom in cars owned by “fast freight” lines. From this time on, however, the percentage of private cars has increased as railroads refused to build specialized freight cars because of high initial costs, rapid technological obsolescence, outside pressure, and managerial shortsightedness.