The possibility to predict, characterize and minimize the presence of spurious harmonic content in the longitudinal
profile of high brightness electron beams, namely the microbunching instability, has become vital to ensure
accurate modeling and reliable operation of radiofrequency and plasma-based linear accelerators such as those
driving free-electron lasers. Recently, the impact of intrabeam scattering (IBS) on the instability has been
experimentally demonstrated by the authors. This work complements that experimental study by extending
existing theories in a self-consistent, piece-wise calculation of IBS in single pass linacs and multi-bend transfer
lines. New expressions for the IBS are introduced in two different semi-analytical models of microbunching. The
accuracy of the proposed models and the range of beam parameters to which they apply is discussed. The overall
modeling turns out to be a fast comprehensive tool for the optimization of linac-driven free-electron lasers
