## 2 Materials and Methods
### Literature Study  
A comprehensive literature study served as a starting point for establishing a clear framework for the analysis of urban sleeping assets. Following [PERSON] et al. [13], we divided the procedure into the four phases of identification, screening, eligibility, and inclusion. For our search of the scientific databases Scopus and Web of Science, we defined different keywords, such as SULP, sustainable urban logistics, underused urban infrastructure/resources, and innovation in urban logistics. For the literature study, we adopted the snowballing method. More than 80 articles were considered relevant to the topic, of which 19 were highly relevant. Due to the scarcity of urban space and strained city infrastructures, the efficient use of existing resources as well as research on urban logistics continuously grow in importance. As shown in Table 1, we categorized previous works according to the sleeping asset categories. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Year** & \multicolumn{4}{c}{**Sleeping Assets Category**} \\ \hline  & & **Neglected** & **Idle Real** & **Underused** & **General** \\  & & **Routes** & **Estate** & **Resources** & **General** \\ \hline [PERSON] and [PERSON] [14] & 2012 & & & X & \\ [PERSON] et al. [15] & 2014 & X & & & \\ [PERSON] et al. [16] & 2015 & & & & X \\ [PERSON] et al. [17] & 2016 & X & & & \\ [PERSON] and [PERSON] [18] & 2016 & & X & & \\ [PERSON] et al. [19] & 2017 & & & & X \\ Dubeaux and Cunningham-Sabot [20] & 2018 & & X & & X \\ [PERSON] and [PERSON] [21] & 2018 & & & & X \\ [PERSON] and [PERSON] [22] & 2019 & X & & & \\ [PERSON] et al. [23] & 2019 & X & & & \\ [PERSON] et al. [24, 25] & 2019 & & X & & \\ [PERSON] [25] & 2020 & & & X & \\ [PERSON] et al. [26] & 2020 & & & & \\ [PERSON] et al. [12] & 2021 & & X & & \\ [PERSON] et al. [27] & 2021 & & & X & \\ [PERSON] et al. [28] & 2021 & & & X & \\ [PERSON] et al. [29] & 2021 & & X & & \\ [PERSON] et al. [30] & 2021 & & & X & \\ [PERSON] and [PERSON] [5] & 2023 & & & & X \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chronological overview of key literature sources and allocation to sleeping asset categories. Figure 1: Applied methods in this study. Research on neglected routes often addresses the potential of shifting freight transport activities from strained infrastructure to alternative routes using waterways [15; 17; 22] or railways [23]. [PERSON] et al. [15], [PERSON] et al. [17], and [PERSON] and [PERSON] [22] analyze the usage of waterways for passenger and freight transportation. While the first study [15] provides an approach for their adaption to urban environments worldwide, the latter two focus on cities in Norway [22] and Vienna (Austria) [17]. Based on a social cost-benefit analysis, [PERSON] et al. [23] introduce a viability model for urban freight transport using railways. By applying the model to the city of Antwerp (Belgium) the functionality was illustrated. Idle real estate is closely related to previous works on logistics sprawl and urban vacancy. [PERSON] and [PERSON] [18] address the impacts of logistics sprawl on cities based on empirical findings, which highlight the longer travel distance of trucks due to logistics sprawl in European and North American cities. Other sources analyze the issue of vacancies. [PERSON] and [PERSON] [20] examine the potential of interim usage concepts for case studies in the German cities Berlin and Leipzig based on expert interviews. In contrast, [PERSON] et al. [12] apply the quantitative vacancy visual analytics method to office buildings in the Australian city of Adelaide in order to address urban vacancy and evaluate the uptake of adaptive reuse as a problem solution strategy. Underused resources, as the third category of sleeping assets, are closely related to passenger and freight transport integration. In this context, [PERSON] and [PERSON] [14] introduce a framework model to integrate the available infrastructure of passenger and freight systems for implementation in the French city of La Rochelle.