In 1890, 5,800 postal railway clerks provided service over of railroad. By 1907, over 14,000 clerks were providing service over of railroad. When the post office began handling parcel post in 1913, terminal Railway Post Office operations were established in major cities by the RMS to handle the large increase in mail volume. The Railway Mail Service reached its peak in the 1920s, then began a gradual decline with the discontinuance of RPO service on branchlines and secondary routes. After 1942, Highway Post Office (HPO) service was utilized to continue en route sorting after discontinuance of some railway post office operations. As highway mail transportation became more prevalent, the Railway Mail Service was redesignated as the Postal Transportation Service.