The high number of bridges in Germany that are in a structurally inadequate condition will lead to a great demand for planning services in the field of bridge construction in the coming years. To meet this demand, the planning process of bridge structures must be accelerated. Digital planning methods such as Building Information Modelling (BIM) form a crucial basis for acceleration. Against this background, this paper will present a solution-based approach for a semi-automated Digital Design Assistant (DDA), based on the German guideline for Railroad Bridges Ril 804.9040. To develop the DDA, the design constraints of the planning and construction process are first evaluated, categorized and prioritized. This includes a full literature review as well as an evaluation of the DDA planning process through use cases in real projects. Based on these results, design constraints are integrated in the BIM model. With the help of programming and the integration of parametric component classes, design results are automated and presented more efficiently and clearly, in comparison to previously labor-intensive modelling. The presentation of the design results are shown in a process chart that summarizes inputs, modelling steps and results of the DDA. In a third step, the parametric component classes are programmed and implemented in a commonly used BIM Software (Revit), and validated in an example project as a Proof-Of-Concept. The results show that the approach developed for the DDA can support the design process and should be implemented for other countries and standards. The design variants generated with the help of a DDA are considered to be both accurate and implementable. However, the case study also shows that the DDA only serves as a support by rapidly generating design solutions, but cannot replace the engineer's role in choosing the right one.