In the early twentieth century, earlier forms of postal transport began to be replaced by regular road-borne service. In the United States, many Railway Post Office (RPO) trains began to be withdrawn from service and the U.S. Post Office Department experimented with the distribution of mail on large buses. These brightly colored red, white and blue Highway Post Office buses were equipped similarly to the old RPO cars. The first HPO service began on February 10, 1941, but expansion was delayed by World War II. More than 130 routes were established between 1948 and 1955. The last HPO service to operate in the U.S. was the Cleveland, Ohio, & Cincinnati, Ohio HPO, which was discontinued in 1974.
The PostBus service in Switzerland is still going strong, having been established in 1906. This evolved as a motorized successor to the stagecoaches that previously carried passengers and mail in the country, with the Swiss postal service providing postbus services carrying both passengers and mail. Although this combination had been self-evident in the past, the needs of each diverged towards the end of the twentieth century, when the conveyance of parcels was progressively separated from public transportation. This split became official with the conversion of PostBus into a separate subsidiary of the Swiss Post in February 2005.
The buses operated by PostBus are a Swiss icon, with a distinctive yellow livery and three-tone horn. The company uses an image of a posthorn as a logo on its buses and elsewhere. On some mountain roads, indicated by a traffic sign of a yellow posthorn on a blue background, the public transport, in particular the postal buses, have priority over other traffic and traffic users must follow instructions by public transport drivers.
In 1906, the first PostBus in Switzerland began service between the capital city of Bern and Detligen with a stop in Radelfingen. The first line crossing the Simplon Pass was inaugurated in 1919. At 6,578 feet (2,005 meters) this high mountain pass between the Pennine Alps and the Lepontine Alps connects Brig in the canton of Valais with Domodossola in Piedmont (Italy). The pass itself and the villages on each side of it, such as Gondo, are in Switzerland. There had been a locally used passage through the mountains here for several centuries, but the pass acquired international significance during the Napoleonic occupation. Between 1801 and 1805, the Simplon Road was constructed by the engineer Nicolas Céard at the direction of the emperor in order to transport artillery pieces through the pass between the Rhône valley and Italy. Since then, the pass has been usable by post carriages, replaced early in the twentieth century by post buses.
The road was periodically improved and in 1950 the cantonal authorities created a plan whereby the pass could be kept open all through the year, and not closed to traffic between October and late April like most Alpine passes at this altitude. The improvements included several lengthy avalanche shelters along the more exposed stretches of road and the expansion of certain road tunnels to accommodate full size tourist coaches which were significantly taller than the post buses used for local passengers. This was completed in 1975.
In 1921, the high mountain Grimsel Pass, crossing the Bernese Alps at an elevation of 7,100 feet (2,164 m), Furka Pass (7,969 feet or 2,429 meters), San Bernardino Pass (6,778 feet or 2,066 meters), and Oberalp Pass (6,706 feet or 2,044 meters) were all opened to traffic on the PostBus system. The source of the Rhine is at Tomasee, a two-hour hike from Oberalp Pass.
The famous three-tone horn was first installed on the post buses travelling on mountain routes in 1923. The Swiss postal authorities began operating the bus lines of the Principality of Liechtenstein starting in 1949. Ten years later, all of the buses of the PostBus system were of the same yellow color.
During most of the 20th century, Swiss post buses were made in Switzerland by either Saurer, Berna or FBW. Today, services are provided by PostBus Switzerland, a subsidiary company of Swiss Post with its headquarters in Bern. The company is responsible for 869 bus routes with 2,193 buses in Switzerland, transporting over 140 million passengers annually on its 7,375-mile (11,869 km) long network. The routes are either operated directly by PostBus itself, or by local bus companies under contract.
PostBus offers extensive services in public, public-private, and private transit, including:
- PostAuto: Bus lines (municipal, regional, long-distance, and vacation transportation)
- PubliCar: Dial-a-bus service for lightly traveled routes
- ScolaCar: Small buses for student transportation
- PostCar: Tourist travel (chartered)
CarPostale France, a subsidiary of PostBus Switzerland, operates bus services in France. The company is headquartered in Lyon, with operations from Haguenau, in Alsace, to Béziers, in Languedoc-Roussillon. PostBus Switzerland also operates the bus service for Liechtenstein.
On September 5, 1937, Switzerland released a 10-centime stamp picturing one of its post buses (Scott #237). Printed in a quantity of 4,9777,000 using the photogravure process on watermarked granite paper, perforated 11¾. These were sold exclusively by the buses. Scott #237 exists in two different paper variants, one with black and red fibers and the other with blue and red fibers. On July 6, 1946, a redrawn version of the stamp was issued (Scott #307). There were 5,559,000 copies printed by Courvasier S.A. using photogravure, perforated 11¾. The designer’s and printer’s name are larger on the later stamps, among many other small differences. For example, the mountain peak is close to the upper picture border on the 1937 stamps while the distance between the peak and the frame on the 1946 version measures 2 mm. Scott #237 measures 37½x21mm while Scott #307 measures 38×22½mm.