On May 18, 1981, the USPS broke an eight-year-old custom by issuing a coil stamp with its own unique design picturing a surrey from the 1890s. Until then, stamps in convenient coil rolls were always of the same design as definitive stamps that were in circulation at the time. There were to be fifty more coil stamps issued through the next fifteen years, each depicting a different conveyance of transportation, ranging from a 1770s carreta, a Southwestern term for a two-wheeled cart, to a 1933 Stutz Bearcat automobile. Conveyances depicted are as entertaining as a 1900s circus wagon, as somber as a 1860s ambulance, and as utilitarian as a 1920s tractor.
The Bureau of Engraving and Printing printed all the Transportation coil stamps, except for three that were printed by private contractors in the 1990s. Line engraved intaglio printing method was used though a few of the last ones were gravure printed.
Transportation stamps exist in an unprecedented array of denominations. Never before had stamps been issued in so many fractional cent values, providing face values exactly matching the rates for various categories of third-class (bulk rate) and quantity-discount mail. Over the life of the issue, there were numerous postal rate changes in first class, bulk, and non-profit bulk mail resulting in new Transportation stamp values being issued.
One of the more fascinating features of the Transportation coils is the tiny plate numbers printed at the bottom of stamps. Stamps with these numbers, appearing at intervals of twenty-four, forty-eight, or fifty-two stamps, depending upon the press employed, are known as Plate Number Coils (PNCs).
The Transportation issue produced a large number of paper, gum, tagging and especially pre-cancel varieties. Pre-cancels were intended for use on bulk mailings that would bypass canceling equipment. Some pre-cancels varieties consisted of overprinted pairs of black horizontal lines, with or without the words of a Service Inscription, while on others the lines and/or Service Inscriptions were an integral part of the stamp design.
The Transportation coils witnessed several interesting features. Early Transportation stamps are distinguished by a comparatively small value, being followed by a 'c'. Later groups express values in larger sized numbers, and lack either a 'c' or a '¢'. The 4-cent Steam Carriage has its value preceded by a zero, being expressed as '04' rather than simply '4', and the 5-cent Circus Wagon and 5-cent Canoe stamps also had their values expressed in this manner. In 1991, the USPS no longer sought to exactly match rates with the face value of stamps; there would be no more fractional values. Instead, 5-cent stamps (for bulk non-profit third class) or 10-cent stamps (for first class presort and regular third class) would be used, and any difference between the face value of the stamp used and the actual postage rate would be paid at the time of mailing. In 1995 the USPS began adding the year date to the lower left corner of stamps, a feature on three Transportation stamps.