The engineer must, of necessity, base his designs within the infrastructure on the component forms that he is himself in charge of determining. Consequently, he cannot completely abdicate responsibility for observing a basic aesthetic quality. He is not usually aware of this joint responsibility, nor is this joint responsibility generally communicated to him, with the consequence that he fails to meet this responsibility. This results in a design gap, which is often concealed with additional design measures and causes inconvenience not only to infrastructure managers, but also in engineering and architectural circles. The aim of this paper is to illustrate the design repertoire of the engineer so that he can use his tools and the knowledge he has acquired to give appropriate shape and expression to his designs according to their function. The terms ‘form logic and ‘form dynamics are introduced and summarised in a form expression pyramid with form art at the top. ^The principles of form logic are derived, on the one hand, by means of the authenticity relationship with natural form-finding processes and, on the other hand, from a historical consideration of the function, and are justified through insights into the theory of architecture for purpose- built infrastructure. In particular, the first two scientific essays include form considerations of integral frame structures made of concrete. By means of the derivation of function units on the bridge object, proposals are indicated for possible form approaches such as e.g. the appropriate use of a circular column for design practice. A third essay shows that form logic can be deliberately developed through structural considerations including the use of an engineers very own tool calculations which additionally have a similar quality of expression. ^Based on single-span overpass bridges of reinforced and prestressed concrete, the process is gone through by means of example calculations and practical designs. On the basis of an appropriate form logic, complementary form dynamic effects for intensifying the form expression including striking analogies with gestalt psychology are examined and transferred to modern bridge construction in a fourth essay. These refinements of form are applied to the overpass bridges made of reinforced and pre-stressed concrete which were developed earlier with form logic, and compared in different design variants. The practical example of a frame bridge with inclined struts, which is currently under construction as part of a new stretch of motorway for ASFINAG is presented. It is important to the author to make the engineer more aware of the scope of his design decisions through his selection of form in the case of infrastructure projects. ^Arguments will be provided from the context of building history and of gestalt psychology, on the basis of which he can make his form decisions using his typically analytical approach. The engineer is thereby provided with aids which allow him to soundly argue for and defend his own designs in aesthetic terms, in order to adequately exercise his design responsibility at least within the infrastructure. In addition, the aim of this paper is to encourage engineers to identify new potential for their work: the creative power of structurally designing.