The objective of this paper is to describe the SEPIA concept and to describe how the development and implementation of it can result in cost and timing improvements in the design phase of the new product development process. SEPIA stands for Simultaneous Engineering Parametric Interaction Analysis. The concept consists of developing a computer program that will receive input from relational databases of primary design variables, determine the interactions between the variables and calculate optimum values for all of them simultaneously, in a format that facilitates decision making.For new vehicle platform programs, the primary design variables are typically mass, manufacturing complexity/cost, performance, regulatory compliance, durability and damageability/repairability. Competitive vehicle analyses have been used to develop benchmark targets for each of the variables listed above and others including NVH, warranty/customer satisfaction, etc.Design decisions need to be based on the interdependencies between the variables. This paper offers several typical scenarios of how these interdependencies can be viewed and how the proposed decision making processes can be implemented.This paper also explores the nontechnical aspects of decision making, with a primary requirement being the development of a trust system between employer and employee, and manager and associate, that transcends the boundaries and barriers of corporate culture, office politics, dysfunctional organizations, gender, racial and generational biases.Reward systems and other recognizable actions must also support the trust building ethic. Every associate may not completely agree with or comprehend a new product plan. However, they will make a commitment to achieve its goals to the extent that management can express and support its commitment for the program. Management has to find and properly utilize the right motivational tools, in some cases, tailored to fit each associate's needs. Trust is the key to this motivational strategy.SEPIA needs to be understood and implemented properly, as an integral part of a total quality management approach. Its merit lies in preventing new vehicle programs from becoming caught in interminable redesgin loops, cost cost overruns, missed market opportunities or outright cancellations. SEPIA seeks to limit these wasteful practices.