Northrop Grumman Advanced Technology Transit Bus

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The Northrop Grumman Advanced Technology Transit Bus (ATTB or "Stealth Bus") was a low emissions, lightweight, composite transit bus developed by the Los Angeles MTA and aerospace specialist Northrop Grumman. The MTA had planned to purchase a fleet of the buses if testing yielded favourable results.[1]

The ATTB used glass composite materials that were developed by Northrop Grumman's subcontractors and used in military aircraft. The light material yielded great strength, and could be molded into sleek, seamless shapes. No bolts or fasteners were required. The bus weighed approximately 10,000 pounds lighter than a conventional bus at the time. The ATTB was powered by a CNG-electric drivetrain in place of the traditional full diesel or full CNG drivetrains. Other sources of power that were considered included LNG, fuel cells, or electricity.[2]


The MTA's predecessor, the Southern California RTD signed a contract in December 1992 with Northrop Grumman and subcontractors to develop the advanced design bus. The project was divided into four phases: concept and design, technology validation, prototype, and field testing.

The project entered the second phase in 1994 with the production of two prototype shells for structural and operations testing. Examples of testing included lowering corners of the bus, a crash test involving a car traveling at 25 mph, and emissions and engine tests[3]

The first prototype was completed in September 1996. Five more prototypes were completed over the following two years. Prototype 1 was submitted for Federal Motor Vehicle Safety Standard testing in May 1997, and prototype 2 was submitted for durability testing at the Atoona Bus Testing Facility. Prototype 3 was shown to various transit agencies across the United States, which included New York, Boston, and Washington. Prototypes 4 to 6 were used for field testing with the LACMTA.[4]

At the conclusion of the ATTB program, a final report was release in April 1999. Drawings and documents relating to the project were made available to interested manufacturers. The bus at the centre of the program never reached production, but many of the ideas have been adopted by other manufacturers.



  • Length: 40' 9"
  • Width: 104"
  • Height: 123.5"
  • Wheelbase: 301.5"


Electric motor

  • Two Kaman Electric hub motors


  • Thermo King REH


  • Front: ZF RLE-66L
  • Rear: beam axle


  • Front: Dayton disc
  • Rear: Knott hydraulic drum



  1. MTA officials consider purchase of buses boasting 'stealth' technology.,, retreived on 2010-11-13
  2. Information : Advanced Technology Transit BusPress release). LACMTA; Northrop Grumman. Retreived on 2010-11-13
  3. LACMTA, Northrop Grumman Corp unveil first lightweight bus test elements of Advanced Technology Transit Bus project. (Press release). LACMTA; Northrop Grumman. Retreived on 2010-11-13
  4. [1]