1. A method for design and modeling of transmission lines, comprising: identifying a critical path in an integrated electrical circuit; formulating design requirements for the critical path; choosing a transmission line core structure from a set of models of core structures in the critical path; identifying neighboring elements of the circuit that may affect a behavior of the core structure; and choosing transmission line geometry parameters based on the design requirements and on simulations using expanded core structure models that comprise models of the core structure and the neighboring elements.