Abstract: A beam comprised of sub-components capable of extending or contracting in overall length is provided. The beam consists of a twin-beam structure that provides travel support for two end beam components that are movable with respect to one another to extend or contract the length of the resulting variable length beam. Extension or contraction of the variable length beam can be accomplished manually or, in a preferred embodiment, by means of a screw drive. The variable length beams facilitate the fabrication of reusable, adjustable width deck-forming panels used in the construction of cast-in-place bridge deck slabs supported by parallel structural beams.