Light weight composites possess high specific strength and modulus and have been widely used in various applications such as transportation, marine, and aerospace. Replacing metallic components with reinforced composites in mass transit helps to lower weight and therefore increase fuel efficiency and decrease maintenance cost without compromising performance. In this work, an air conditioning cover roof door on a mass transit bus was designed, analyzed, and manufactured for a 'form-fit-function' replacement of an aluminum component. Novel design using thermoplastic composites materials and thermoforming processing technology were demonstrated to form the part. Innovative composite materials namely thermoplastic polyolefin (TPO) as the outer skin and a ribbed lofted glass mat thermoplastic (GMT) inner liner to provide structural stiffness and strength were used. Weight savings of 39% and reduction of free-standing deflection of 42% were realized using the composite approach compared to the metallic counterpart. © 2008 Elsevier Ltd. All rights reserved.