The 1886 Steam Carriage was one of the earliest self-propelled vehicles. The body consisted of a wide wooden framework mounted on top of a horizontal boiler barrel. Shallow water tanks were placed on either side, forming bench seats that provided enough room for 10 passengers. This novelty never gained popularity, however, due to the fact that it was noisy, dirty, and uncomfortable. U.S. #2451 is part of the popular Transportation Series. The Transportation Series contains 59 stamps with engraved designs featuring modes of transportation from the baby buggy to the racecar.