# On the Road to Circular Public Procurement: Case, Variations, and Potential Actions in Germany
## 1 Introduction
### Research Gaps and Research Questions  
Circular public procurement is a specific type of green public procurement (GPP) [23]. GPP is defined by [24] as 'a process whereby public authorities seek to procure goods, services and works with a reduced environmental impact throughout their life cycle when compared to goods, services and works with the same primary function that would otherwise be procured'.  
[PERSON] et al. [25] analysed the state of the art of GPP research in detail. They provide an extensive overview of existing literature and future trends as well as a comprehensive GPP model with barriers and support factors. Their article also shows three particular research gaps:  
1. The GPP discussion 'has mostly focused so far on the specific impacts of GPP implementation' [25]. Strategies to implement GPP for specific product areas are analysed less frequently. As shown in Section 1.1, sustainable, circular tyres make an interesting study case in this context.  
Circular public procurement is underrepresented in GPP research. In this context, [PERSON] et al. [25] refer to the environmental impacts of proposed projects, which may include'recycled material'. Apart from the brief mentioning of one circularity aspect, [25] does not consider any other circularity aspects in-depth, not even in the state of the art.
3. [PERSON] et al. [25] also provide information on the countries where GPP studies took place. Germany is not mentioned in their list.  
While the findings of [PERSON] et al. [25] are mainly focused on the broader impact of GPP implementation, another widely studied research topic is GPP and its interrelations. Specifying this aspect, [PERSON] [26] showed the importance of external stakeholders on GPP. Environmental certification is another influencing factor for GPP and also for its relation to its stakeholders. In this context, [PERSON] [27] found that GPP's influence on the market and its pressure in requiring certificates is positively associated with this certification practice.  
Regarding CE aspects specifically, the Web of Knowledge database provided 16 hits for the search term 'circular procurement' in the area of management, business, economics, and law. Based on further analyses of titles and abstracts, eight articles appeared to be relevant in the context of this study [28; 29; 30; 31; 32; 33; 34; 35]. Several CPP studies focus on a specific country case. In this context, four national studies were identified, including two from the EU member state The Netherlands (which include suggestions for public procurement in Sweden), as well as studies on Oman and Pakistan. German case studies were not identified in this review. Relevant product groups covered by the studies include building products, textiles, and ICT products. Specific analyses on circular public procurement in the automotive sector and the procurement of circular types are missing from the identified list. An additional analysis of grey literature showed several short examples for national procurement practices, in particular in EU documents such as [23]. There is also a German guide on environmental public procurement of types in general [36]. Key CE aspects such as recyclability and recycled content are, however, not addressed specifically. As this second example shows in particular, a gap regarding circular tyre procurement remains, also due to the poorly established practice of the topic. On this basis, two research questions were formulated:  
1. What is the current state of circular public tyre procurement in Germany?
2. How could circular public procurement of these products be promoted?  
After this introduction, Section 2 presents the materials and methods used to answer our research questions. Section 3 provides information on procurement patterns and barriers to procuring sustainable CE tyres, and solutions to address these barriers. The article finishes with a discussion in Section 4 and an outlook in Section 5.