Rapid Transit Series

The Rapid Transit Series (RTS) city bus is a long-running series of transit buses that was originally manufactured by GMC Truck and Coach Division during 1977, in Pontiac, Michigan. First produced in 1977, the RTS was GMC's offering of an Advanced Design Bus design (the other entry was the Grumman 870 by competitor Flxible) and is the descendant of GMC's prototype for the U.S. Department of Transportation's Transbus project. The RTS is notable for its then-futuristic styling featuring automobile-like curved body and window panels; the Advanced Design Buses were meant to be^{[by whom?]} an interim solution between the high-floor transit buses that preceded them, such as the GMC New Look (which had a curved windshield, but flat side glass and body panels), and modern low-floor buses that would facilitate passenger boarding and accessibility. Most current buses are now made by specialized coach manufacturers with flat sides and windows.

Production of the RTS transitioned from GM to Motor Coach Industries (under its Transportation Manufacturing Corporation subsidiary in Roswell, New Mexico) in 1987, moved to NovaBus in 1994, and finally moved to Millennium Transit Services (MTS) in 2003. Production ceased with the closing of MTS in 2009.

The RTS was offered in 30-foot (9.14 m)-, 35-foot (10.67 m)-, and 40-foot (12.19 m)-long models and was built using a modular design that allowed the same parts to be used for all three lengths, the longest of which could seat up to 47 passengers. It was originally powered by either 6- or 8-cylinder versions of Detroit Diesel's Series 71 two-stroke diesel engine channeled through an Allison V730 or ZF 5HP-500 transmission. Later models could be powered by a 6-cylinder Series 92, or the 4-cylinder Series 50 engines.

The RTS is the descendant of the GMC RTS-3T, its prototype built for the Transbus project; the RTS-3T was preceded by the RTX (Rapid Transit Experimental), a turbine-powered prototype produced in 1968 that had been under development since 1964. Both the RTX and the RTS-3T Transbus prototype had a similar design as the production RTS, though there were numerous detail differences, such as the prototypes having a less-rounded body design, a one-step entryway, and (in the case of the Transbus) a 45-foot (13.72 m) length. RTX used the same GT-309 gas turbine engine that had previously been fitted to the Turbo Titan III and Turbo-Cruiser II/III concept vehicles along with a "toric" continuously variable transmission. RTX also used smaller wheels and a "kneeling" suspension design to reduce first-step height by 4+1⁄2 in (110 mm), aiding boarding, and the interior floor height was 21 in (530 mm), 7 in (180 mm) lower than a contemporaneous "New Look" bus. However, the passenger capacity of a 40-ft bus was reduced from 50 to 29.

Wanting a backup plan in case the Transbus project was abandoned, GMC decided to modify the RTX/Transbus design and in 1970 began the RTS-II project (designating two axles) that became the earliest RTS with the first prototype being assembled in 1973 at which point the project went onto hiatus. Though closer to its predecessors than the production models, the RTS name debuted with this prototype. After the project was revived in 1974, GMC would later withdraw from the Transbus project and focus their energies on the RTS, which was billed as an Advanced Design Bus representing a "transitional" or "interim" step towards a low-floor bus to facilitate boarding and disembarking. GM announced it was ready to accept orders for the RTS in October 1975.

In September 1985 GMC announced that due to lower than expected, or poor sales of their RTS series buses, that it was in the process of trying to sell or close its transit bus building business, and then later announced that they have sold its RTS design, and patent rights, and bus manufacturing equipment and production line to Transportation Manufacturing Corporation (TMC) of Roswell, New Mexico, a subsidiary of Motor Coach Industries in May 1987, though the two companies completed a joint order for the New York City Transit Authority to prepare TMC for the production. TMC eventually sold the design and patents to NovaBus in September 1994 in the midst of an order for the Massachusetts Bay Transportation Authority. Production under NovaBus continued until 2002 when NovaBus left the U.S. market and concentrated on its latest LFS low-floor design.

Production was revived, however, by Millennium Transit Services, which announced plans to manufacture the bus in both high and low-floor configurations at the shuttered TMC facilities in Roswell. However, after poor sales and failure to fulfill orders, Millennium ceased production on the RTS and went out of business in 2009. In September 2011, MTS re-entered the market and showcased its latest RTS product at the 2011 APTA Expo in New Orleans. It also announced plans to introduce a 42.5-foot (12.95 m) version of the standard floor RTS, which would go into production in the near future. MTS ceased to exist sometime after 2012 after failing to win any substantial bus orders, as the market for high-floor buses (using rear door mounted wheelchair lifts) had essentially vanished by that point; transit agencies had turned to New Flyer Industries, Orion, Gillig, NovaBus, and NABI and their low-floor models equipped with front door wheelchair ramps.

Through the history of the RTS, there have been six generations of production plus two experimental variants (one of which not having made it beyond the prototype stage).