###### Abstract  
Motivated by the urgent need to discover innovative and sustainable approaches to address the strain on urban resources, this paper introduces a novel concept proposing the utilization of \"sleeping assets\". These sleeping assets encompass three distinct categories of urban infrastructures: neglected routes, idle real estate, and underused resources. By harnessing these assets, cities can alleviate the intense competition for land, traffic infrastructure, and parking areas. The findings presented in this paper are derived from an extensive literature study and expert interviews conducted with relevant stakeholders from Hamburg, Paris, Stockholm, and Vienna. Building upon the most pertinent insights from the literature and a structured content analysis of the interviews, we outline the advantages of employing sleeping assets for urban logistics initiatives. Additionally, we identify seven main categories of implementation barriers that must be taken into account. The results of this study reveal political and legislative barriers as one of the major impeding factors in initiating the utilization of sleeping assets. To address these barriers, this paper points towards crucial leverage for cities and provides an outlook on possible forms of sustainable urban logistics implementation. Thus, this work can support researchers as well as practitioners from city administrations and urban logistics interested in using sleeping assets by encouraging the exploitation of unused potential and avoiding particular implementation pitfalls. s +
Footnote †: journal: Applied  
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raise a critical question: how can we design sustainable urban freight logistics to meet the rising demands of modern society while minimizing the ecological footprint? In this context, the implementation of a \"Sustainable Urban Logistics Plan\" (SULP) plays a vital role. According to Eltis, the European urban mobility observatory, \"A Sustainable Urban Mobility Plan is a strategic plan designed to satisfy the mobility needs of people and businesses in cities and their surroundings for a better quality of life. It builds on existing planning practices and takes due consideration of integration, participation, and evaluation principles\" [11]. The major objectives of an SULP encompass enhancing the efficiency and cost-effectiveness of passenger and freight transport; reducing air and noise pollution, GHG emissions, and energy consumption; and contributing to the overall improvement of urban environments for citizens, society, and the economy [11]. Despite these clear objectives, [PERSON] et al. state that urban logistics planning is only being gradually integrated into the scope of urban planning, indicating a need for increased attention to this crucial aspect [10]. Moreover, within the urban setting, certain infrastructures experience greater strain than others. Recognizing and utilizing these underused resources represent fundamental steps towards innovative opportunities to meet the stated SULP objectives. A comparison of the average GHG emissions per ton-kilometer of the individual modes of transport in freight logistics shows that heavy goods vehicles cause significantly higher emissions than rail transport, inland waterway transport, and maritime shipping [12]. Nevertheless, in 2021, only 5.4% of all freight transport in the EU was carried out by rail and 1.8% by inland waterways [13]. Therefore, we see these infrastructures as currently neglected resources, especially in urban freight transport. Furthermore, vacancies pose a problem in terms of the efficient use of scarce urban space. It is not entirely clear how vacancies occur in existing buildings, for example, before they reach the final state of obsolescence [12]. Moreover, vacancies do not only occur in buildings, but can also be observed in car parks. Another area that has potential for increasing utilization efficiency in urban logistics is resources that are currently underutilized, e.g., all types of (partly) empty running vehicles for both passenger and freight transport.