Recent trends in the automotive industry show growing demands for the introduction of new in-vehicle features (e.g., smart-phone integration, adaptive cruise control, etc.) at increasing rates and with reduced time-to-market. New technological developments (e.g., in-vehicle Ethernet, multi-core technologies, AUTOSAR standardized software architectures, smart video and radar sensors, etc.) provide opportunities as well as challenges to automotive designers for introducing and implementing new features at lower costs, and with increased safety and security. As a result, the design of Electrical/Electronic (E/E) architectures is becoming increasingly challenging as several hardware resources are needed. In our earlier work, we have provided top-level definitions for three relevant metrics that can be used to evaluate E/E architecture alternatives in the early stages of the design process: flexibility, scalability and expandability. These definitions provide qualitative and quantitative measurements of ability of an architecture to accommodate changes. Following up on our earlier work, in this paper, we provide a detailed definition for these metrics, and define a methodology and related methods to compute these specific metrics for E/E architecture alternatives. Efficacy of proposed methods to quantitatively evaluate these three metrics has been illustrated via a hypothetical case study.