While Greyhound and GM continued to develop a unique parlor bus design which was to become the PD-4501 Scenicruiser, GM constructed a bus incorporating some of its features such as picture windows, air suspension, optional air conditioning and full silversiding. Greyhound bought the first one in the spring of 1953 and eventually operated 1,253 Highway Travelers.
The PD-4104 was the first of many General Motors buses to use the slanting window pillars, a design theme which remained with the intercity line to its end in 1980 and was also used on all GM new-look transit buses. The PD-4104 became the standard of the industry as 5,065 were produced during eight years. Many were still providing reliable service after 25 to 30 years of operation.
Information from the Bus World Encyclopedia of Buses - 1988