The Role of Micro Fulfilment Centers in Alleviating, in a Sustainable Way, the Urban Last Mile Logistics Problem: A Systematic Literature Review

Abstract

This systematic literature review has as its aim to discuss how the use of micro fulfilment centers can help logistics and supply chain professionals in alleviating the urban last mile logistics problem. This systematic literature review adapts the SALSA approach, the PRISMA 2009 checklist, and the PRISMA 2020 flow diagram, while its validity is based on the utilization of the qualitative CASP checklist. In addition to the above, certain inclusion/exclusion criteria were used. The findings of this review underline that micro fulfilment centers are a key new approach in terms of alleviating the last mile logistics problem, in urban areas where space is extremely limited via a reduction in CO₂ emissions, the use of new technologies not only in operations but also in the delivery of goods and the increase in customer satisfaction. This is an original and breakthrough literature review as it covers a gap in the existing literature that has to do with the role of micro fulfilment centers in urban areas in terms of alleviating the last mile logistics problem, a topic about which not much have been written until now as it is quite novel. This literature review gives a clear path for the researcher of the future in terms of approaching the urban last mile logistics problem via the lens of the use of micro fulfilment centers, while it contributes to the urban logistics industry in several ways.

1. Introduction

According to the world bank [1], today, around 56% of the world’s population, which can be translated to roughly 4.4 billion inhabitants, is living in cities. This number tends to continue to increase with the urban population and is expected to rise by 2050 to a staggering 70% of the people living on the planet, while more than 80% of the global GDP (Gross Domestic Product) is already generated in cities [1].

In addition to the above, the increase in urban e-commerce deliveries, which were only reinforced by the recent COVID-19 pandemic, has led to an increase in the volumes that needed to be handled by urban last mile logistics, something that had vast and multiple implications in the urban logistics and therefore for the urban population [2].

From the above, we can understand that there is an urgent need for better solutions in terms of the urban last mile logistics challenges that business is facing and will face soon. Such solutions that can alleviate the last mile logistics problem, as it will be described in the results part of this research, can also have a positive sustainable impact in urban areas.

One of the main components of the urban last mile logistics problem, which inevitably is continuously enlarged by the above-mentioned global urbanization, is the space factor. Space in urban areas is limited, especially in the centers of the cities where renting and buying space is extremely expensive, something that increases urban last mile delivery problems.

The lack of space in urban areas creates problems in warehousing and distribution, since warehouses and distribution centers need to stay in the cities’ perimeter, something that also increases traffic congestion, delivery problems, CO₂ emissions, decreases customer satisfaction, etc.

Several solutions have been implemented in the last years towards addressing that situation, e.g., mobile fulfilment systems for fresh food real-time delivery solutions [3], the use of micro fulfilment centers, the use of dark stores, etc. This systematic literature review is focused on the implementation of micro fulfilment centers in urban areas towards alleviating the last mile logistics problem.

The problem that this research highlights is the warehousing and fulfilment/distribution centers problem in urban areas, since they need to use huge spaces and therefore are situated in the perimeter of the cities. This fact, per se, contributes in a negative way to the urban last mile logistics problem since delivery companies need to pick the products and deliver them to the end-user by following routes that might include even the crossing of the whole city from the distribution facility to the end user. In addition to the above, environmental, financial and societal concerns have arisen that need to be addressed.

In order to address that problem, this systematic literature review aims to unveil some of the limitless possibilities that can spring from the adoption of micro fulfillment centers in urban areas in terms of alleviating, in a sustainable way, the last mile logistics problem. This review will mainly focus on issues like the lack of space in urban areas, CO₂ emissions, traffic congestion, delivery time, consumer satisfaction under the prism of the use of new technologies like, e.g., the use of robotics in the micro fulfilment centers, etc.

Towards reaching the above-described aim, this systematic literature review addresses the following research question:

How can the use of micro fulfillment centers help in alleviating the urban last mile logistics problem in a sustainable way?

Moreover, we need to add that in this systematic literature review, two main areas were covered extensively, namely the urban last mile logistics and the problems that they are facing and, of course, the implementation of micro fulfillment centers in urban areas to tackle issues, like the lack of warehousing space, decreasing CO₂ emissions, improving traffic jam conditions and increasing delivery efficiency and thus customer satisfaction.

Finally, the contribution of this systematic literature review will be multidimensional, as it will pave the way for the researchers of the future towards new research paths (e.g., the use of new technologies in sustainable city logistics, etc.) and can fill the gap in the existing literature in terms of the combination of the use of micro fulfilment centers, the urban last mile logistics problem, the triple bottom line and the use of technologies and can provide insightful managerial insights for logistics professionals, citizens and city authorities.

2. Materials and Methods

Systematic literature reviews are usually used to address the following (Atkinson & Cipriany, 2018, cited in [4]):

• To find information regarding the research topic or even to find potential gaps in the literature that can be addressed by this specific study or others in the future.
• To synthesize conclusions in an area that is covered by ambiguity.
• To help researchers in their decision-making and to give some potential practice guidelines (Atkinson & Cipriany, 2018, cited in [4]).
• To retrieve information about all the available literature on a specific topic in order to answer a predefined, by the researcher, main research question (Higgins & Green, 2011, cited in Atkinson & Cipriany, 2018, cited in [4]).

As we can understand from the above, when we follow the systematic literature review approach, to meet all of the above-mentioned goals, we need to have a very carefully, detailed and coherent research strategy in place and of course an embedded research protocol (Higgins & Green, 2011, cited in Atkinson & Cipriany, 2018, cited in [4]).

In this section, we are going to discuss the protocol that this systematic literature review used to answer, in a comprehensive way, the main research question. The protocol that is described in this chapter was chosen because it gives an easy-to-follow approach in terms of describing the steps that were followed by the author and because it gives us a clear and concise way in terms of ensuring which papers were chosen and why, from which sources, if the sources were legitimate, which approach the author chose in order to gather all the relevant information, if the research question was answered in a coherent way, etc.

The protocol that was used for this research by the author gives a clear description of the overall approach that was used in terms of what was reported according to the PRISMA 2009 checklist (see Supplementary Materials) (in terms of what is included in each part of the research, like in the abstract, introduction, methods, results and discussion) and the methodological steps that were followed according to the SALSA framework. In addition, as part of the SALSA framework that has been followed, a well-known and easy to use validation tool is used, which utilizes a set of predefined simple questions (CASP checklist) to assess the validity of the approach regarding the defining, in terms of whether the main elements of the research that needed to be addressed, were addressed.

2.1. Predefined Eligibility Criteria of the Literature Used

In the following lines, we describe the predefined eligibility criteria that were chosen to be used in this systematic literature review regarding the chosen literature. These criteria are the following:

2.1.1. Criterion 1

Only journals of high status indexed in SCOPUS and WEB OF SCIENCE were used. The reason behind that decision was that such journals publish articles that undergo a rigorous double-blind peer review process. In addition to that, some grey literature was also used in order to fill the gap in the existing literature regarding all aspects that are discussed in this literature review.

2.1.2. Criterion 2

All chosen articles were relevant to topics that included disciplines like supply chain management, urban logistics, micro fulfilment centers, last mile logistics, A.I. (Artificial Intelligence), new technologies, warehousing automation, robotics, sustainability, warehousing, etc., and their combination

2.1.3. Criterion 3

All chosen articles were written in English and were published after 2015.

For the above-mentioned criteria to be followed, a structured approach was followed by the author.

• STEP 1

The author established access to high-tier journals via tertiary databases, like Springer, Link Taylor and Francis, EBSCO, universities’ libraries, etc. Also, access was established to specific and legitimate grey literature via internet sources.

• STEP 2

Specific strings of keywords, which we will examine in the following parts of the methodology chapter, were chosen to cover the umbrella topics under which the author needed to search for the suitable-to-use literature.

• STEP 3

All articles to be chosen were subjected to an initial “screening”, which was based on reading the abstract of the article. If after reading the abstract of the article the author made sure that the article was relevant (was written in English, published after 2015 and was under the umbrella of at least one of the relevant topics or a combination of them), the author had the opportunity to start reading the article in order to determine whether or not he could use parts of its content.

• STEP 4

A thorough reading of the article in question was taking place, in order to make sure that the specific article was the needed one to be used for this research.

An important point that needs to be underlined and made clear is that systematic literature reviews are an important “tool” of research, which assist us in the analysis and dissemination of evidence via rigorous and transparent methods/protocols [5]. Therefore, in this literature review, only legitimate sources that originated from well-known tertiary databases, as discussed in step 1, were used. In addition to the above sources though, this systematic literature review has also utilized, to some extent, some gray literature as well. Gray literature, or evidence not published in commercial publications, can be the catalyst towards important contributions to a systematic literature review [5]. It can include academic papers, web pages, pdfs, theses and dissertations, etc. [5]. This systematic literature review used some, e.g., web sources, which are considered grey literature, and which were deemed legitimate and valid, like CASP, Newswire, etc.

2.2. Screening Process (Inclusion/Exclusion Criteria)

The screening process established by the author was deemed necessary due to the large number of papers that needed to be reached to create an exhaustive, if possible, database to be used for this systematic literature review.

The “base” of the screening process was the inclusion/exclusion criteria that were adopted and which were used as a first scrutiny front of screening regarding the potential, to be used by the author, papers. These inclusion/exclusion criteria were used to determine which published materials would be used in the next steps of the screening process.

2.2.1. A. Inclusion Criteria

• Use of peer reviewed studies that specifically discuss the role of the use of micro fulfilment centers in alleviating the urban last mile logistics problem;
• Use of peer reviewed studies that discuss the technological, operational, societal and economic impacts of micro fulfilment centers;
• Use of peer reviewed studies that discuss the urban last mile logistics problem and its potential dimensions and/or potential solutions;
• Use of peer reviewed studies that discuss innovations, technology and other relevant parameters, which are part of the operation of micro fulfilment centers;
• Grey literature from legitimate sources only, which adds valuable information towards answering the research question;
• Only peer reviewed studies that originated from legitimate tertiary databases were used;
• Only peer reviewed studies that were published after the year 2015 were included;
• Only peer reviewed studies and grey literature that were written in English were included.

2.2.2. B. Exclusion Criteria

• All studies that were not focused in urban areas were excluded;
• All studies that were not focused on urban last mile logistics were excluded, unless in the, e.g., context of examining the whole supply chain, they had something valuable to add to the research;
• All studies that were published before the year 2015 were excluded;
• All studies that lacked real-life applications were excluded;
• All studies that were discussing technologies that were not used or related to the technologies used in micro fulfilment centers were excluded;
• All grey literature that did not follow to the above criteria (1–5) was excluded;
• All peer reviewed papers and grey literature that were not written in English were excluded.

After the implementation of the above-mentioned inclusion/exclusion criteria, the author proceeded with the screening process, which took place on two levels. The first level had to do with the screening of the title and the abstract of each paper that was fulfilling the inclusion criteria, while the second level had to do with the screening of the whole papers that was qualified after the first screening level (Covidence, nd., cited in Karaoulanis, 2024 [4]). The screening process can be found in the following

Table 1. The screening process.

The Screening Process
Level 1	Level 2
Screening of the title and abstract of the qualified from the inclusion/exclusion criteria papers	Screening in full the papers that were qualified from level 1

:

2.3. Methodology

The methodological approach that this literature review follows was realized via the use of the SALSA framework. In addition, the overall screening report of the methodological approach can be depicted via the PRISMA 2020 flow diagram, which we can see in the following Figure 1.

In the following Table 2, we can see the categorization of the selected papers according to their topic and author/date.

Table 2. Selected paper categorization by topic.

Topic of Selected Journals	Authors
Micro-Fulfilment Centers	[3,6,7,8,9,10,11,12,13,14,15]
Urban Last Mile Logistics	[1,16,17,18,19,20,21,22,23,24,25,26]
New Technologies	[4,11,27,28,29,30,31,32,33,34,35]
Research Methods	[36,37,38]
Warehousing	[39,40,41,42,43,44,45,46,47,48]

Table 2. Selected paper categorization by topic.

Topic of Selected Journals	Authors
Micro-Fulfilment Centers	[3,6,7,8,9,10,11,12,13,14,15]
Urban Last Mile Logistics	[1,16,17,18,19,20,21,22,23,24,25,26]
New Technologies	[4,11,27,28,29,30,31,32,33,34,35]
Research Methods	[36,37,38]
Warehousing	[39,40,41,42,43,44,45,46,47,48]

Figure 1. The PRISMA 2020 Flow Chart [37].

Figure 1. The PRISMA 2020 Flow Chart [37].

The depiction of the proportion of the peer reviewed papers that was chosen for this systematic literature review, as they can be seen in Table 2, is materialized in the following Figure 2.

As we can see from Figure 2, not only all relevant topics were discussed in this review, something that guarantees its holistic approach and improves dramatically the possibilities of the comprehensive answer to the research question, but in addition, the author managed to establish an equilibrium between the discussed topics.

As we already discussed, this review follows the SALSA framework. The SALSA framework comprises different steps, which are described in the following

Table 3. Methodological approach (SALSA framework) [49].

The Salsa Methodological Approach
STEP 1	Begin with a very basic pre-research/brainstorm concepts and keywords/select the appropriate sources to search (SEARCHING)
STEP 2	Use your inclusion and exclusion criteria/perform a detailed read and ask yourself a series of critical questions regarding the quality of your readings (APPRAISAL)
STEP 3	Extract the significant information from each article (SYNTHESIS)
STEP 4	Analyze what you have found (ANALYSIS)

.

According to Grant and Booth (2009; cited in [50]), the SALSA framework is heavily used to determine the search protocols that a systematic literature review should follow. SALSA can guarantee the accuracy, systematization, exhaustiveness and reproducibility of the research in question [50].

Furthermore, the SALSA framework can be found as part of many scientific work that uses it in order to reduce risks related to publication bias and to increase the acceptability of the submitted (Del Amo et al., 2018; Grant & Booth, 2009; Malinauskaite et al., 2019; Perevochtchikova, 2019, cited in [50]).

In this chapter, we will discuss steps 1 and 2 as they are giving us the methodological basis, while steps 3 and 4 will be discussed in Section 3 and Section 4, which correspond to the “synthesis” and “analysis” steps of the SALSA framework.

2.3.1. Searching Strings and Types of Databases

The tertiary databases that were used in this research were mainly Taylor & Francis, Springer Link, EBSCO and a few online university libraries, especially for the first steps of the SALSA method/approach.

The above-mentioned tertiary databases were used because they are the repository of thousands of legitimate, relevant, scientific blind peer review papers that are indexed by Scopus and/or Web of Science, something that guarantees their legitimacy, from a scientific point of view, and that all papers that were scrutinized were published in high-tier journals.

Also, the searching tools that such tertiary databases use are very useful, easy to use and provide a coherent and quick search, something that is crucial in terms of time and resource consumption. For example, the databases depicted in the above Table 3 use searching tools that can include/exclude the author, the date, the title of the document and different other searching details, which help the researcher to be able to follow the initial inclusion/exclusion criteria.

To be able to come up with an initial selection of relevant papers that fulfil the first inclusion/exclusion criteria of the date, language and relevancy of topic, the research used several search strings. Therefore, the researcher initially used several terms, like “urban logistics”, “micro-fulfilment centers”, “last mile logistics”, etc. In addition, several phrases were used for an initial search, like e.g., “last mile logistics problem”, “Urban last mile logistics”, “urban warehousing”, “urban traffic congestion”, “logistics sustainable solutions”, etc.

Since the above search keywords and key phrases were initially used, their combination helped in the generation of multiple search strings, which included specific operators (like “and”, “or”), which enhanced the accuracy and speed of the search results.

For example, some of the strings that were used in the initial screening phase of this research are the following:

• STRING 1: “Urban logistics” AND “micro -fulfilment centers”;
• STRING 2: “Urban warehousing” AND “Urban last mile logistics problem”;
• STRING 3: “last mile logistics problem” AND “new technologies in warehousing”;
• STRING 4: “urban last mile logistics” AND “sustainable solutions”;
• STRING 5: “warehousing robotics” AND “micro -fulfilment centers”, etc.

The above-mentioned strings were also used in a different combination, which was achieved via the use of the “OR” operator instead of the “AND” one. In that way, the researcher managed to find papers that combined different variables of the research, but also, he managed to find papers that were discussing the above-mentioned variables separately. This initial step was fundamental towards selecting the needed peer reviewed studies towards answering the research question.

2.3.2. Quality Assessment of the Findings

The next step regarding the SALSA framework has to do with the appraisal of the review and the inclusion/exclusion criteria. While the latter ones have been already discussed, the appraisal of the review, to be accurate and comprehensive, needs to follow a specific methodological approach. Nevertheless, there is a lack of consensus regarding the methodology that needs to be used to assess the methodological quality of a systematic review [51].

This review uses the CASP checklist approach/methodology. The CASP methodology has been chosen between different other methodologies, like, e.g., the AMSTAR and AMSTAR 2 ones as they were deemed the most suitable for a systematic literature review, since they are very “user -friendly” as they are based on a very simple methodology, which has to do with answering a specific set of questions. Apart from that, the CASP checklist methodology was chosen because it is the most suitable one, compared to the other available, for social science systematic literature reviews (CASP, n.d., cited in [4]). In addition, the CASP checklist is a tool that can enable the researcher to systematically assess the trustworthiness, relevance and results of published papers (https://casp-uk.net/, n.d.a)

Of course, we cannot omit that the CASP methodology has some limitations, which include the following:

• Potentially not including items that provide a rationale for sample size and recall bias [38].
• Relatively minimal use of the participant’s voice [38].
• The tool might emphasize more the methodological aspects of the research, something that potentially can overshadow other essential components, such as, e.g., the relevance of the study to a specific research question [52].

Overall, since there is no perfect tool, as all have their pros and cons, the CASP checklist is considered a very good tool to be used in systematic literature reviews with very high usability in health care and social sciences [51]. The CASP checklist comprises 10 questions that need to be answered by the researcher via the use of simple answers like “YES”, “NO”, “Can’t tell” (CASP, n.d. cited in [4]):

• Did the review address a clearly focused question?
• Did the author look for the right type of paper?
• Do you think all the important relevant studies were included?
• Did the review’s author do enough to assess the quality of the included studies?
• If the results of the review were combined, was it reasonable to do so?
• What are the overall results of the review?
• How precise are the results?
• Can the results be applied to the local population?
• Were all important items considered?
• Are the benefits worth the harms and costs?

(CASP, n.d. cited in [4]).

In the following

Table 4. CASP questions and answers (CASP, n.d. cited in [4]).

CASP Checklist for This Systematic Literature Review
Questions Checked	Answers
	Yes	No	Can’t Tell
Did the review address a clearly focused question?	✓
Did the author look for the right type of papers?	✓
Do you think all the important relevant studies were included?			✓
Did the review’s author do enough to access the quality of the included studies?	✓
If the results of the review were combined, was it reasonable to do so?	✓
What are the overall results of the review?	See the results part
How precise are the results?	See the results part
Can the results be applied to the local population?	✓
Were all important items considered?			✓
Are the benefits worth the harms and costs?	✓

, we can see the answers to the CASP questions regarding this literature review.

The use of the above-described methodology is extremely useful research-wise since it can become a powerful tool in the hands of the researcher, as it can help him in being systematic by making sure that all relevant/important factors that are involved in the research were taken under consideration (CASP, n.d. cited in [4]). In the following lines, we can see the detailed answers to the CASP checklist questions:

▪

Did the review address a clearly focused question? Yes, the research question has clearly addressed the problem in a very coherent way and by taking into consideration all the relevant variables.

▪

Did the author look for the right type of paper? Yes, the author followed a strict protocol, which included specific inclusion/exclusion criteria, which were followed in detail.

▪

Do you think all the important relevant studies were included? Cannot tell. The answer here simply denotes the obvious, that it is impossible to know if all relevant important studies were included although the main scientific tertiary databases were scrutinized by the researcher.

▪

Did the review’s author do enough to assess the quality of the included studies? Yes. The researcher/author is considered to be an expert in the field; therefore, it can be a safe enough assumption that he knows which data can be considered as quality or not. In addition, all specific and strict protocols in terms of searching, screening, analyzing and synthesizing steps were followed, something that solidifies even more the “yes” answer to this question.

▪

If the results of the review were combined, was it reasonable to do so? Yes. The reason behind this answer is that the research itself had as its main goal to answer the main research question that was based on the variables of the problem in question (dependent, independent, intermediate and control variables). Therefore, the combination of the research results had as its main goal depicting a necessary combination between the variables in a way to answer the main research question. Consequently, yes, it was very reasonable to combine the results of the research.

▪

What are the overall results of the review? The answer to this question, which is also the answer to the main research question, can be found in the synthesis and conclusions part of this research.

▪

How precise are the results? The answer to this CASP question is that they are very precise but only as precise as the secondary data that were used. Of course, the right use of the protocol was able to provide us with high-quality research, something that, by definition, increases the precision of the results of this research.

▪

Can the results be applied to the local population? The answer to this question is that the results can be applied to the local urban population since they are combining data that cover the research topic in a very extensive and holistic way. Also, the results are of global applicability because they are dealing with a problem that we can encounter on a global scale.

▪

Were all important items considered? The answer to this question is “can’t tell”, simply because it is almost impossible to know if all relevant high-quality literature has been reached, although the researcher was able to have access to a high volume of relevant literature via the use of many high-quality tertiary databases.

▪

Are the benefits worth the harms and costs? Yes. This literature review not only can be seen as the springboard for the researcher of the future in terms of helping her in conducting field research on a topic that is extremely contemporary and important but also can be used from organizations, companies, municipalities, etc., as a tool that can enhance people’s lives in urban areas; plus it can provide a sustainable future to both companies that operate in the urban logistics industry.

In addition to the above, for further qualitative validation, CASP has developed a checklist that follows the same philosophy but is focused solely on the qualitative aspects of the research [36]. This list comprises ten questions, which are answered in the same way (Yes, no, cannot tell) and are the following:

• Was there a clear statement of the aims of the research?
• Is a qualitative methodology appropriate?
• Was the research design appropriate to address the aims of the research?
• Was the recruitment strategy appropriate for the aims of the research
• Were the data collected in a way that addressed the research issue?
• Has the relationship between the researcher and participants been adequately considered?
• Have ethical issues been taken into consideration?
• Was the data analysis sufficiently rigorous?
• Is there a clear statement of findings?
• How valuable is the research? [36].

The detailed answers for this systematic literature review are the following:

• Was there a clear statement of the aims of the research?

• YES. The research in the introduction part clearly stated its aim.

2.

Is a qualitative methodology appropriate?

• YES. This is a systematic literature review.

3.

Was the research design appropriate to address the aims of the research?

• YES. The research design of this systematic literature review was based on well-known and valid systematic literature review research designed as described in the methodology part.

4.

Was the recruitment strategy appropriate for the aims of the research

• CANNOT TELL. This is a systematic literature review, which does not involve field research.

5.

Were the data collected in a way that addressed the research issue?

• YES. All collected data were scrutinized and covered all variables involved in the research in a way that they can assist the researcher in answering the research question.

6.

Has the relationship between the researcher and participants been adequately considered?

• CANNOT TELL. This is a systematic literature review, which does not involve field research.

7.

Have ethical issues been taken into consideration?

• YES. All information that was used was referenced in an appropriate way to pay respect to the authors of the chosen papers. In addition, the content of this systematic literature review was carefully crafted to not harm any person.

8.

Was the data analysis sufficiently rigorous?

• YES. The data gathered in its analysis and synthesis followed well-established and respected scientific protocols, as described in the methodology part.

9.

Is there a clear statement of findings?

• YES. In the results part, all findings were clearly presented

10.

How valuable is the research?

• The research is extremely valuable as it deals with an issue (urban last mile logistics) that is very contemporary and involves the wellbeing of billions of people around the world. In addition, it touches on the element of micro fulfilment centers, a recent development in urban areas that might be part of the solution to the urban last mile logistics problems. The findings of the research can have vast societal, managerial and business-wise implications.

3. Results

In this part, we will present the findings of this systematic literature review. The findings will be synthesized in a way that they can help us to answer the research question. The results part has been divided into sub chapters, which discuss each one of the variables that are examined in this research. The results are presented in two levels. On the first level, we present the basis of the problem by highlighting the current situation. Therefore, at this level, what is discussed is the urban last mile logistics problem, the current situation with warehousing in urban areas and the lack of space and the micro fulfilment centers. The second level presents the role of the use of micro fulfilment centers in alleviating the urban last mile logistics problem.

3.1. The Urban Last Mile Logistics Problem

As we already briefly discussed in the introduction part, the big majority of the global population nowadays is living in urban areas. The European commission estimates that about 85% of the global population lives in urban areas, while, mainly due to a different definition of what is “urban areas”, the United Nations (UN) estimate that this number is closer to 55% [24]. Urban freight flow, the last years, presents a trend of steady growth, which has as its driving forces, apart from the increased in urban population, in the above-mentioned increased urbanization, densification, globalization, online and omni-channel retailing and urban economic development [16].

In terms of delivering goods, the final stage in the delivery process, which of course is the one that brings the goods to the doorstep of the consumer, is the stage that faces most of the problems, and it is the costliest part of the supply chain as well. It is the least efficient, the most expensive and the most polluting part of the whole delivery process (Goodman, 2005; Spiegler, 2004, cited in [27]). It is impressive that, e.g., it comprises up to 28% of the total cost of delivery (Goodman, 2005; Spiegler, 2004, cited in [27]). Therefore, it is considered a problem for the logistics industry, and finding a way to alleviate it is extremely important, while it is known as the logistics last mile problem [27].

The high increase in the urban global population, as described in the previous paragraphs, in combination with the high economic development, especially in mega-cities and the e-business prosperity, especially after the COVID-19 era, is highlighting the increased importance of the last mile logistics problem in urban areas. Lat mile logistics as part of the urban logistics is focusing on delivering packages/goods to the preferred from the end customer location, instead of buying the goods from a brick-and-mortar shop. The result is an increase in the number of shipments in urban areas [53].

In fact, a colossal number of companies nowadays are responsible for delivering parcels, meals, groceries and palletized wholesale freight in urban areas. Each one of these companies faces several challenges that are connected to the way they operate (e.g., if they are specialized to a particular good or service, if they operate out of their own distribution centers, if they employ their own drivers and operate their own vehicles, etc.) [22]. All these companies can be considered as part of the urban last mile logistics problem as they contribute to it, but also, they are affected by it. In a way, it can be considered a vicious cycle.

As a result, cities all over the world, especially in the last years, are trying to rethink their mobility policies, especially in light of their environmental and quality-of-life objectives [21]. One of the scarcest resources of cities is urban space. Since the shift towards efficient and zero CO₂ emissions urban logistics has already taken place, companies that operate in urban areas need to have space to unload, cross-dock, consolidate and stock goods closer to the end customer [21]. Sustainable urban logistics has an important impact in urban populations, and therefore, there is an increased need for better logistics management, including environmentally friendly transportation and the need to take under consideration political and societal issues [54].

Since the increased transport activity has negatively impacted city residents and the environment in urban areas, increasing traffic congestion and increasing noise pollution and road infrastructure damage, companies that deliver goods in urban areas started to turn towards solutions in warehousing and distribution closer to the end customer.

In addition to that, the growing online shopping sales and the increased demand for swift delivery have put tremendous pressure on online retailers to locate their warehouses and fulfilment centers in urban areas closer to the end user towards direct access to the consumer markets [55].

This is when the Urban Distribution Centers (UDC) solution started to be materialized as a solution that could minimize urban transport activity via goods consolidation [26]. For example, such facilities started to be materialized close to malls, airports or even at the very centers of cities (Allen; Browne; Woodburn; Leonardi, 2012, cited in [26]).

In the following sections, we will present our findings in terms of urban warehousing, the rise of micro fulfilment centers and how their use can be a catalyst in alleviating the last mile logistics problem in urban areas.

3.2. Warehousing in Urban Areas

As we discussed until now, the increase in the urban population, which, as we saw, led to an increase in urban deliveries, also increased the need for warehousing in urban areas. According to [39], warehousing is an extremely important component of supply chains, as without the proper warehousing planning, companies would not be able to serve the end customer due to increased distance to market.

Ref. [17] denotes that supply chains that are characterized by their high performance and low impact are the ones that benefit from the proximity of their logistics facilities (including warehousing) in proximity to goods’ destinations. In addition to that, ref. [40] states that urban warehousing plays a critical role in terms of helping retail and delivery companies to serve consumers faster. The same author underlines that urban warehousing can only be seen as a necessary condition that logistics companies need to consider implementing successfully for their transition to an urban logistics system that is efficient and sustainable [40]. What is also very important here though is that this transition entails certain important challenges, e.g., the co-existence with the local urban communities [40].

It is interesting here to add that according to the results of a research that was conducted by [48], growing spatial disparities in warehousing-related environmental externalities in urban areas (e.g., air pollution, traffic congestion, etc.) need to be addressed via the implementation of land-use policies, job related policies, financial incentives and environmental regulations. As the same author adds, with the rapid expansion of the warehousing industry in major metropolitan areas, environmental impacts associated with its activities have been growing in the last decades [47]. This is indicative of the significance of the allocation of the space for warehousing implementation in urban areas. Space is not only rare in urban areas, but also expensive, while distance from the warehousing and distribution facilities can be considered the most space-extensive components of logistics and the supply chain [45]. Under this prism, the complexities that can arise from the implementation of warehouses in urban areas where space is extremely limited can be easily understood. This space problem is the driver for more decentralization of warehousing regarding urban areas. The trend of warehouses to move away from urban centers in the perimeters of the cities is also known as “Logistics Sprawl” [41].

According to [43], over the last decade, warehousing and distribution centers have decentralized to the peripheries of urban areas because in such areas, land is much cheaper than, e.g., in the centers of the cities. Supply chain and distribution companies want to build more modernized and larger facilities, something that automatically means the use of more space [43]. Therefore, it is obvious from the above that land prices “push” large warehouses away from central urban locations of large cities [43].

Of course, what is also important is that although space is rare in urban areas and land prices are very high, two factors that have a negative impact on moving warehousing closer to large cities’ centers, the proliferation of globalization and the expansion of e-commerce, have led, in the last years, to an increase in the establishment of warehousing facilities in urban areas [46]. This fact, per se, is of course a negative indicator in terms of its negative influence on the increase of air pollution, noise pollution and traffic congestion in urban areas [46], while it does not increase paragons that are important regarding the last mile logistics problem, like speed in delivery, efficiency and customer satisfaction, as warehouses and distribution centers are usually located in the perimeter of the cities due to the lack and high cost of urban space.

The “problem” of expensive land prices in the center of urban areas is also highlighted in terms of the warehousing industry’s facilities and location establishment by Kang [44]. According to ref. [44], in the last years, the logistics industry had to reinvent itself and to go through a restructuring, as there was an increased need for the transportation of large volumes of goods quickly and reliably. Since this was the case, the warehousing industry went through a similar transformation, which was accompanied by a change in facility sizes and locations; therefore, large warehouses started to be built in the outskirts of the big urban centers [44]. The reason behind this shift was because in the trade-off that suddenly appeared, the gains from the lower land prices in the outskirts of the cities and the increased scale in operations outweigh the increase in transport costs that followed the decentralization of warehouses from the central urban areas [44].

This space problem in urban areas tried to be addressed by companies in many ways. For example, “high-density storage” was one of them via which stores were trying to solve space-wise problems, including local warehousing of their goods, via utilizing mobile racks mounted on rails, so that a strong engine could move whole blocks of racks aside, opening an aisle and enabling access to a specific rack, something that tried to decrease the pick time and increase the warehousing space [56].

Furthermore, combining shipping with warehousing and distribution is a solution that some of the biggest logistics companies in the world have been following the last years. Such solutions can benefit customers due to the seamless end-to-end solution with the involvement of fewer logistic service providers, less complexity, more speed in delivery and more control and visibility [12].

Such space and warehousing/distribution problems in urban areas tried to be addressed in the last years with the implementation of a new solution, the micro fulfilment centers. What is a micro fulfilment center and how it is involved in the alleviation of the urban last mile logistics problem will be discussed in the following sub chapters.

3.3. What Are the Micro-Fulfilment Centers

Micro fulfilment centers can be seen as a recent development in terms of distribution in urban areas, while they also include warehousing solutions. According to [10], micro fulfilment centers refer to small fulfilment centers that are in the city center and function as an advanced base for quick, usually, e-commerce services. Ref. [15] indicates that micro fulfilment centers started to be used in urban areas to achieve quick deliveries and profitability. In fact, the above-mentioned authors propose the establishment of a network of these centers in urban areas in a way that they will achieve the highest possible customer proximity.

Certain industries, like the grocery one, are the ones that receive increased benefits from the implementation of micro fulfilment centers in urban areas. Micro fulfilment centers can be considered small distribution warehouses placed strategically in urban areas with a goal of fulfilling orders [9]. They typically have a much smaller footprint than the usually gigantic warehouses that are used by the retailers as they usually occupy an area between 2000 and 5000 square feet [9].

The utilization of micro fulfilment centers in urban areas, which are usually heavily populated and in which high density and traffic can create enormous problems for logistics operators, customers and society, is extremely important. Ref [11] underline that micro fulfilment centers have, as their main goal, fulfilling orders for goods, including both the in-store picking of goods and online ordering of goods, while orders are fulfilled by using both a picker-to-goods (P2G) model and an automated goods-to-picker (G2P) one [11].

In addition to the above, ref. [8] highlights that the modern e-commerce development and the increased use of chain stores made it extremely important for logistics companies to set up many micro fulfilment centers in the city, which can provide last mile logistics services to their customers in a quick and efficient way.

The importance of micro fulfilment centers is also highlighted by [57], as they state that the increase in automated micro fulfilment centers by retailers who are into grocery delivery can assist them in terms of achieving their growth potential.

In the next lines, we will highlight the positive influence of the use of micro fulfilment centers on alleviating the urban last mile logistics problem, by focusing in the use of new technologies in the micro fulfilment centers, the decrease that they can achieve in terms of the CO₂ emissions in urban areas, the decrease in the delivery costs and the increase in customer satisfaction as a result of higher-level logistics services provided.

3.4. How Micro Fulfilment Centers Can Alleviate the Urban Last Mile Logistics Problem

In this part of this systematic literature review we will discuss the role that micro fulfilment centers are playing in terms of alleviating the urban last mile logistics problem.

3.4.1. Use of New Technologies in Micro Fulfilment Centers

As we have seen until now, the use of micro fulfilment centers in urban areas is extremely useful for retailers and especially the e-retailers who can now reach their end customers in less time.

Micro fulfilment centers make extensive use of automation tools, something that positively impacts efficiency, fast delivery, etc. As we have already discussed, a micro fulfillment\t center fulfills orders for goods, including both the in-store picking of goods and the online ordering of them [11]. The orders are fulfilled by using both picker-to-goods models and automated-goods-to-picker models, which replenish the goods to the automated-goods-to-picker system from store shelves, which also serve the picker-to-goods model [11].

According to [58], a workstation like that usually implements bots carrying order totes, while other bots carrying product totes transfer the product totes to the order totes. In addition to this bots technology, cameras may be provided in order to capture images of the product and/or order totes to identify the contents of totes and to identify positions where goods are to be picked from the product totes and placed into the order totes [58]. In that way, the whole delivery process is positively impacted.

A workstation in a micro fulfilment center that uses bots for the order totes usually comprises a robot for the automated transfer of goods between the product and the order totes, while it might also include a workstation for the operator to perform manual transfer when needed [58].

Another important element of micro fulfilment centers that can have a positive impact on the urban last mile logistics problem is the use of semi-automated solutions. According to [14], semi-automated solutions that can be found today in micro fulfilment centers include pick to cart or pick to a robot and may incorporate automated sortation to quickly consolidate orders. This quick consolidation of orders can also improve efficiency and fast delivery, which is an important component of the urban last mile logistics problem.

Of course, today, micro fulfilment centers move towards full automation with the aim of minimizing reliance on manual labor and simultaneously to be able to maximize fulfilment accuracy and productivity [59]. Therefore, new technologies, like the integration of robotic arms and artificial intelligence for picking or the use of mobile robots in the form of goods-to-robot (GTR), are some of the new automation approaches that we can see in the micro fulfilment center [59].

The above-mentioned AS/RS systems can improve utilization and productivity, while through them, several systems have been developed, like the autonomous vehicle storage and retrieval systems (AVS/RSs), which are based on autonomous vehicles and which allows users to flexibly change the number of vehicles in the system to obtain the required throughput [33], or like the SBS/RS, which is a shuttle-based system, which compared to AS/RSs, can support higher throughput capacity [33].

According to [35], AS/RS revenue within micro fulfilment centers is expected to reach as high as US$1.2 billion by the year 2027, with the uptake primarily to be pinpointed in the grocery and FMCG industries.

3.4.2. CO₂ Emissions and Traffic Congestion

Traffic congestion in urban areas in the last years has increased, in some cases dramatically, mainly due to the growth of e-commerce, which skyrocketed after COVID-19. This increase has also imposed more pressure on the courier, express and parcel sector (CEP), which now has to tackle the “city last mile logistics” problem and, inevitably, to come up with solutions that would be able to satisfy customers and all involved stakeholders in the city framework, like, e.g., city councils, citizens, regulatory bodies, etc. [60]. According to [20], the shift that took place in the last years in the consumers’ behavior in terms of switching from the in-person buying from brick-and-mortar shops to online shopping, although it has decreased commuting for shopping reasons, has increased, e.g., the parcel delivery volumes, especially in urban areas, something that also has increased the associated CO₂ emissions in such areas.

In addition to the increase in CO₂ emissions, other areas that were also impacted are the traffic density, the air pollution and noise [28]. Although direct delivery from with distribution trucks, mainly from regional depots directly to the end customer might have been the case and completely justified, this is something that is not considered valid anymore, especially since we need to take into our consideration the big growing numbers of the needed deliveries in urban areas [28]. Micro fulfilment centers, via their horizontal collaboration inside the city limits, were found to be a viable solution towards that direction, especially in the inner -city centers [60]. In addition, micro fulfilment centers near customers became the facilitators of the increased need for fast delivery, as they managed to minimize the distance from the end user/customer [10].

Furthermore, it is important here to underline that the use of micro fulfilment centers can help parcel delivery companies to significantly reduce harmful city CO₂ emissions and of course traffic congestion [61]. The way to do it might be by reshaping the last-mile delivery ecosystems [61]. According to the same article, which used the case of the city of London as an example, using micro fulfilment centers across the city of London to fulfil just half of the e-commerce orders could significantly reduce the traffic volume and harmful CO₂ and in general air emissions [61]. This is an extraordinary result and highlights why the use of micro fulfilment centers in urban areas, even in mega cities like London, can make a sustainable difference for the local population.

In the same wave-length, the report titled “The sustainable Last Mile: Faster, greener, cheaper” underlined that the use of micro fulfilment centers across mega cities like London to fulfil just half of the e-commerce orders could significantly reduce traffic volumes and harmful air emissions, as a 13% reduction in delivery traffic, which equates to about 320 million fewer delivery vehicle miles being achieved [61]. The result could be the lowering of delivery-vehicle-related emissions in London by 17% by 2025 [61].

In general, the use of micro fulfilment centers in city logistics can be seen as a determining factor in terms of reducing the number of fossil-combustion-powered commercial vehicles, which are travelling daily within the city limits, solely for the transportation of goods [23]. In this way, we can say that they drastically contribute to the reduction in the negative effects of urban logistics activities, like air pollution, but also, noise, traffic congestion and even traffic accidents [23].

A network’s optimization via the consideration of the links between the nodes in the last mile logistics (e.g., based on the vehicle routing problem) can be achieved via the use of historical traffic and consumers’ data, which are rarely leveraged in the context of the last mile delivery problem (Pan et al., 2017, cited in [18]). Via such an approach, cost definition will be reached by a more holistic perspective, which now can include environmental costs apart from only, e.g., delivery costs, etc. (Pan et al., 2017, cited in [18]).

Of course, in terms of efficient delivery with lower costs, less CO₂ emissions, increased speed and in general better quality of customer service, factors that are crucial parts of the urban last mile logistics problem, new technologies in the form of delivery drones, unmanned vehicles and electric vehicles can be combined with the implementation of micro fulfilment centers in urban areas [30].

The decrease in CO₂ emissions, as has been already discussed, in combination with lower traffic congestion due to the implementation of the micro fulfilment center solution, can be considered an important contributor to the “planet “part of the triple bottom line of urban logistics. In addition, increased customer satisfaction through quick delivery and less traffic congestion are paragons that address the “people” part of the triple bottom line. Finaly the lowering of delivery costs, as we will discuss in the following Section 3.4.3, addresses the “profit” part; therefore, we can argue that the use of micro fulfilment centers is an extremely sustainable solution in urban areas.

3.4.3. Delivery Costs

The increased demand for quick commerce services, including quick deliveries via the use of micro fulfilment centers, was a revolutionary evolvement in urban last mile logistics in the last years. One of the problems here is the high costs and operational efficiency [10].

Ref. [13] argues that micro fulfilment centers can integrate space optimization, operational scalability and high efficiency in terms of operations. Via the use of micro fulfilment centers, consumers can get their items faster, but in addition, retailers can save on the cost of order packing and transportation [13].

According to a Capgemini report (2019, cited in [18]), home delivery is the most impacting contributor to the overall supply chain costs at a level of around 40%. The biggest portion of these costs are part of the last mile delivery, and they can be categorized as variable ones, which means in simple words that if, e.g., as the online delivery volumes increase, they provoke an increase, as well, to the last-mile delivery costs (Capgemini, 2019, cited in [18]). The results of this report are indicative in terms of the problem that can be alleviated via the use of micro fulfilment centers in urban areas.

Although the implementation of micro fulfilment centers in the urban web, due to their proximity to the end customer, can vastly help in alleviating the delivery costs, in addition, it is imperative for logistics companies and retailers to use new delivery methods. The use of, e.g., environmentally friendly transport technologies can make a more efficient use of the urban infrastructure and decrease delivery costs (Deckert, 2016, cited in [19]). Fewer diesel powered delivery vehicles, especially in city centers, and their replacement by electric ones can be a solution (Kloeckner, 2017, cited in [19]). In addition, solutions like load bicycles can be another way to use other transport routes (Kloeckner, 2017, cited in [19]).

One potential solution towards that direction might also be the use of parcel lockers in the centers of the cities where micro fulfilment centers are also located. Such solutions imply lower delivery costs than home deliveries, which usually are extremely costly as we noted in the previous paragraphs, since they can increase the delivery density and can drastically reduce failed deliveries [62]. Such benefits are more significant in urban than in rural areas due to lower parcel locker investments and annual costs [62].

Finally, we need to underline that lowering delivery costs via the implementation of micro fulfilment centers has a positive impact on improving the “profit “part of the triple bottom line of urban logistics.

3.4.4. Optimal Customer Service

Nowadays, postal services and 3PLs have been under immense pressure in terms of delivering goods to the end customer, especially in urban areas, mainly due to the increased demand of e-commerce [7]. In addition to the above, ref. [29] underlines the importance of achieving the appropriate level of customer service in urban last mile logistics, while parallel environmental concerns need to also be addressed. Such findings underline the need for the improvement of urban last mile delivery strategies towards meeting customers ‘expectations and increasing their satisfaction [7].

The importance of customer satisfaction in terms of providing a sustainable solution towards solving the urban last mile logistics problem is highlighted by [34], since they stress that last mile delivery is an important part of all business since it is the part of logistics that can directly encounter the end customer and therefore can affect customer satisfaction in multiple ways.

The rise in quick commerce in the last years has become one of most important issues that urban last mile logistics need to face due to the intensifying competition for faster delivery between the logistics companies and retailers [33]. According to the same authors, a fulfilment service that can integrate various logistics processes, while increasing the delivery speed, has emerged in the last years as it is positioned near the customer. This service/solution is the micro fulfilment center [33].

The use of micro fulfilment centers can be a strong determinant in terms of improving customer satisfaction in the urban last mile logistics part of supply chains. According to [35], delivery times are getting faster and faster, down to a matter of hours for specific products. The increased demand for alternative shopping experiences, like, e.g., click-and-collect, made the use of micro fulfilment centers highly beneficial, while both customer attraction and retention now rest heavily on more effective inventory management and of course localized delivery capabilities from the part of the vendor [35]. Such micro fulfilment center solutions are underpinned by cube- or shuttle-based AS/RSs, orchestrated by specific management systems, which increasingly in the last years incorporate Artificial Intelligence (A.I.) capabilities [35].

In recent research by [42], the results showcased that order-processing in warehouses and distribution centers, if combined with flexible and transparent distribution processes, can eventually contribute to the overall customer satisfaction in terms of meeting his/her expectations. Under this prism and since the above-mentioned processes can be allocated in urban micro fulfilment centers, one can argue that they can radically improve overall customer satisfaction.

The optimization of customer service via the use of micro fulfilment centers can also be considered a sustainable approach in last mile logistics as it improves the “people” part of the triple bottom line of urban logistics.

3.5. Some Disadvantages of the Use of Micro Fulfilment Centers

Although, as we saw in this chapter, the use of micro fulfilment centers in urban areas can have a strongly alleviating role in terms of the last mile logistics problem, many argue that their implementation can also have some cons.

According to [63], the use of micro fulfilment centers can impose negative results to retailers and logistics companies because they can have an expensive set up, especially when there is no ownership of sustainable properties in the city web; although they can decrease delivery costs as we saw already, they can also increase them when working with local last mile carriers. In addition, they usually need to carry increased inventory; thus, a higher capital commitment is needed, and they can add more complexity to the existing fulfilment strategies, while they require more investments in adequate technology to work properly and efficiently [63]. Finally, they are not proper for all products (e.g., for furniture, etc.) [63].

Many might argue that in some cases, the use of micro fulfilment centers in urban areas can create problems like fragmenting urban freight deliveries, potentially increasing traffic congestion, increasing air pollution and increasing traffic accidents and noise. In fact, last mile solutions are not ideal as they will have several limitations [25]. As we have already presented in the results part, the use of micro fulfilment centers can help towards the direction of avoiding such problems via their combination with the right delivery vehicles. Recent research by [64] underlined that there is trend between logistics companies for smaller and lighter vehicles for last mile deliveries in urban areas, like the use of bicycles and tricycles or the sue of other types of light commercial vehicles [64]. The combination of micro fulfilment centers and light vehicles can be the catalysts towards the avoidance of such implications that have to do with noise increase, traffic congestion, air pollution, etc.

3.6. Conclusions of the Results

Urban last mile logistics have changed dramatically in the last years. The pinnacle of this change is what is called “last mile logistics problem” in urban areas. Logistics and retail companies have struggled in the last years to find a sustainable solution to the above problem. The implementation of micro fulfilment centers in urban areas provides a drastic solution in terms of alleviating the urban last mile logistics problem, as it helps in decreasing CO₂ emissions, improving efficiency and customer satisfaction and decrease delivery costs. In other words, micro fulfilment centers can positively affect the triple bottom line of the urban last mile logistics towards alleviating their problems.

In general, we can say that micro fulfilment centers present many advantages that revolve around the following (Kellermayr -Scheucher et al., 2021, cited in [6]):

Picking costs and times are heavily reduced (via automation).

Accuracy in terms of order fulfilment, which results in fewer wrong deliveries (again via the use of automation).

Last mile delivery costs and time needed are decreased due to proximity to the end user/customer.

Operating and leasing costs decreased due to lower space needed.

Inventory management efficiency is increased (more SKUs per square foot can be handled).

Goods–return flow management becomes more efficient.

Energy consumption and CO₂ emissions are decreased due to less distance needed for the final delivery of goods (Kellermayr-Scheucher et al., 2021, cited in [6]).

In addition, if new technologies, especially in terms of delivery (e.g., electric vehicles, drones, unmanned vehicles, use of A.I. in routing, etc.) will not be combined with the implementation of micro fulfilment centers, many of the above-mentioned advantages can be lost. In addition to that, when implementing a micro fulfilment center, other cons need to be taken under consideration like their expensive set up, the increased inventory and the increased complexity that they might add to the logistics planning of the company in question.

4. Discussion

In this part, we will discuss the results of this systematic literature review, while we will give a clear answer to the research question.

4.1. Answer to the Research-Question

The research question that this systematic literature review addresses is as follows: how can use of micro fulfillment centers help in alleviating the urban last mile logistics problem?

The answer to the research question is the combination of the below findings.

According to our findings, the use of micro fulfilment centers can be a catalyst in terms of alleviating the urban last mile logistics problem in a sustainable way. It can help in decreasing the CO₂ emissions in urban areas via detailed and AI-assisted routing planning and the consolidation of goods and thus fewer delivery routes and the use of modern state-of-the-art delivery ways, like unmanned and electric vehicles, drones, etc. In that way, the “planet” part of the triple bottom line can be addressed, something that is a huge step for urban logistics towards a sustainable solution.

In the same wavelength, the above approach can assist in decreasing traffic congestion in urban areas since less delivery vehicles will be needed for the goods’ delivery and since the distance to the customer has been decreased due to the positioning of micro fulfilment centers in the centers of the cities and in general in strategic urban locations, which are characterized by their proximity to the end user. In that way, customers/citizens will have many benefits, which can be faster delivery, less noise due to decreased traffic congestion, less traffic accidents and of course, due to the decrease in CO₂ emissions that we discussed in the previous paragraph, they will breathe cleaner air, something that might even increase their life expectancy. All of these can be extremely important sustainability elements that micro fulfilment centers can provide towards alleviating the urban last mile logistics problem as they address successfully the “people” part of the triple bottom line.

In addition to the above, automation and use of new technologies in the micro fulfilment centers will also decrease order fulfilment times, something that will increase customer satisfaction and efficiency in delivery. Finally, due to the high automation that is used in micro fulfilment centers, less distance from the customer and fewer vehicles needed for the goods’ delivery or use of vehicles with zero fuel consumption, like drones, electric vehicles, etc., delivery costs for both customers, retailers and logistics companies will be decreased. In that way, not only a big part of the last mile logistics problem, which is delivery cost, will be addressed, but also logistics companies will manage to increase their profits. In that way, the “profit” part of the triple bottom line can also be addressed successfully.

Such results can be used to alleviate the urban last mile logistics problem to a high extent, something that underlines the importance of the use of micro fulfilment centers, a solution that includes warehousing, consolidation and the delivery of goods to the end user in a sophisticated and efficient way, which also has a very sustainable footprint.

4.2. Originality and Novelty

Although much as been written the last years regarding the importance of the last mile logistics problems, especially in urban areas, and the use of micro fulfilment centers, not much has been written in terms of the correlation of the two above paragons towards the implementation of a sustainable solution in urban areas, which can be achieved via a CO₂ reduction, decrease in traffic congestion, increase in customer satisfaction, decrease in delivery costs, etc. Only scattered pieces of information via various studies were able to be found; therefore, the task of combining all of this information in order to provide a new and unique point of view regarding the micro fulfilment centers’ role in urban last mile logistics is imperative.

Therefore, this systematic literature review is a novel and original one as it addresses a problem that is not only very important but also quite novel. The researcher pinpointed a gap in the existing literature that had to do with the combination of the use of micro fulfilment centers and the urban last mile logistics problem towards a sustainable solution, via the lens of delivery costs, decreased traffic congestion, customer satisfaction air pollution, etc.

4.3. Managerial Implications and Real-Life Applications

The managerial implications of this this research are multiple. Supply chain and logistics managers can use the insights of this review to design new ways for their urban last mile deliveries and to facilitate their execution based on the triple bottom line approach (People–Planet–Profit). They can not only use the micro fulfilment centers to alleviate their last mile logistics problem, but also, they can invest in micro fulfilment centers’ automation and their combination with new delivery technologies to become “greener” and more customer efficient. This new approach in urban last mile logistics can become a “game changer” for many companies that operate in the urban logistics industry and can have huge implications from a managerial point of view as it can become a competitive advantage that such companies will be able to leverage.

The results of this study can also have vast positive implications in terms of customer service, as the use of micro-fulfilment centers in urban areas can increase the responsiveness of that last “leg” of supply chains, especially with everything that has to do with online orders. Therefore, logistics managers can use the solutions provided by this research to improve customer satisfaction towards an increased customer retention rate.

In addition, municipalities, especially in large and crowded urban areas, can encourage the use of micro fulfilment centers via certain incentives, the implementation of new regulations, etc., because that will help them to create a more viable environment with less pollution and less traffic congestion for their citizens. Also, policy-makers might find the results of this review very useful as they now might need to consider the facilitation of the redesign of the urban space in large cities in a way that more space can be created for the establishment of more micro fulfilment centers in areas where space is very expensive and extremely limited. It is important to not forget that for policy-makers, some of the most important aspects that are connected to e-commerce are related to cost reductions in transportation, facilitation of the needed administration and communication between the involved stakeholders, innovations at the market level and environmental issues, e.g., reductions in the associated CO₂ emissions [31].

Finally, other stakeholders that will be able to benefit from the implementation of this novel approach in urban last mile logistics are the residents of the cities, especially the mega-cities, who will be able not only to experience a better, with less air pollution, environment, but also, as consumers, they will be able to experience fast deliveries.

4.4. Managerial Insights

The importance of the insights that this review is offering to managers in the industry is huge. Logistics managers who are dealing with urban last mile logistics will be able to leverage the given insights to decide their new green and efficient approach in terms of their urban deliveries. Their design of the last leg of their supply chains now will be based on new facts, which will involve the use of micro fulfilment centers towards more sustainable solutions for the urban populations, plus an increased efficiency in terms of the last mile deliveries. Some food for thinking, which might also be a potential direction of the researcher of the future, is the spatial organization of the micro fulfilment centers in the inner-city web in a way that it will decrease, even more, the delivery costs, delivery times and CO₂ emissions. The consolidation of goods, which can take place in micro fulfilment centers, might be the determinant for less delivery costs and less air and noise pollution as it will incur less transportation miles inside the city.

In addition, increased automation can be the catalyst for many logistics companies, which, in an era that is characterized by a shortage of skilled employees in the supply chain and logistics industry, they started to consider other solutions that will help them to manage the gap in their human resources.

Finally, it is important to suggest a potential approach for urban logistics managers, which can be based on data analysis of historical data of customers’ orders. The analysis of such data, especially with the use of Artificial Intelligence, can indicate patterns of customer behavior, rush hours, tendencies and needs for speed and delivery options that can be used to help us navigate an optimal use of the micro fulfilment centers in combination with the use of new technologies in delivery, like drones, electric and unmanned cars, robots, etc.

4.5. Further Research Perspectives

Although much has been written until now regarding the city’s last mile logistics, its correlation, as we have already discussed, with the implementation of micro fulfilment centers has not been investigated thoroughly until now.

This review opens new roads for the researcher of the future in terms of investigating, maybe on a quantitative basis, the implications of this review in the context of urban last mile logistics. Perspectives that have to do with the calculation of the decrease in CO₂ emissions in urban areas that might be impacted by the use of micro fulfilment centers might be a good extension of the managerial insights that this review brings forth.

In addition, further research from the perspective of investing in new technologies towards the complete automation of micro fulfilment centers (e.g., instead of semi-automated solutions) and their combination with new technologies in terms of delivery to the final customer might be a good next step for the researcher of the future. For example, the use of drones, unmanned vehicles, electric vehicles, delivery robots, etc., in combination with the use of micro fulfilment centers might be a potential future field of research.

As we briefly discussed in the previous paragraph, the implementation of a novel model that would take under consideration historical data and via the use of A.I. will be able to identify patterns and trends in customer service in a way that they will help us to optimize the use the micro fulfilment centers with the use of new technologies in both warehousing and delivering, and this might be part of future research as well. The exploration of such a model might also be the basis of future research.

Another important factor that might be considered by the researcher of the future is the financial dimension of the implementation of micro fulfilment centers and how it impacts the bottom line of both retailers, end customers and logistics companies.

Also, all of the above can be discussed, as part of a future research, in the context of smart cities and the use of industry 4.0 technologies, in a way that, e.g., traffic congestion and route optimization problems can be addressed drastically.

4.6. Comparison with State-of-the-Art Research on the Topic

Although there is a gap in the literature regarding the topic of this study and limited papers were able to be part of the final selection stage, there are several other state-of-the-art research papers that discuss parts of the investigated problem and its solution. In the following lines, we will present certain peer reviewed papers that consider the state-of-the-art micro fulfilment center domain, and we will compare their results with the findings of our systematic literature review.

According to research from [6] titled “Micro-fulfilment centers in E-grocery deliveries”, location and technology selection decisions and several other warehousing criteria are factors related to the use of micro fulfilment centers in alleviating the urban last mile logistics problem [6]. This research is in complete alignment with the findings of our research.

On the same wavelength, in the research titled “Sustainable urban last mile logistics: A systematic literature review” [25], the authors underline the integration and combination of multiple last mile logistics alternative concepts towards the solution of the last mile logistics problem, something that is in accordance with the findings of our research since we highlighted findings that have to do with the integration, e.g., of new technologies, A.I. and new delivery options (e.g., drones, unmanned cars, etc.).

In recent research [32], the use of new technologies plays an important role in alleviating the last mile logistics problem via the establishment of transparency, efficiency and consistency, which then can increase customer satisfaction. These findings are also in accordance with our research’s findings, which indicate a very strong correlation between the use of new technologies and customer satisfaction as well.

4.7. Critical Analysis of the Existing Literature

The existing literature that was used for this systematic literature review, after being scrutinized, presented a lack in terms of how the use of micro fulfilment centers with the utilization of new technologies in both operations and deliveries has an impact on all aspects of the triple bottom line (e.g., CO₂ emissions, customer satisfaction, delivery costs). Only scattered pieces of information were able to be allocated; therefore, it was imperative that the combination of those pieces needed to be achieved in a rigorous and academically correct way by the author.

The general finding was that the use of the micro fulfilment centers in urban areas is extremely beneficial in terms of alleviating the urban last mile logistics problem, from many perspectives. Literature that was used indicated that micro fulfilment centers can not only alleviate the last mile logistics problem in a sustainable way but also can introduce space-wise, solutions that can solve issues that are correlated with warehousing in such areas. Therefore, we can say that there is a congruence in the existing literature in terms of the findings connected to this systematic literature review and that the gap in the literature was addressed by the author in a comprehensive way as the correlation between the variables that were examined was rigorous and unique.

In terms of the frameworks that were utilized by this systematic literature review in the methodology part, the PRISMA 2009 checklist, the SALSA framework and the predefined eligibility criteria, which was accompanied by the inclusion/exclusion criteria, were found by the author to be very suitable for this kind of this research, and although they have specific limitations that were explained in the text, they provided a rigorous and scientifically accurate and valid research approach. The assessment of the validity of the research was based on the CASP checklist, which was extended into the CASP checklist, which was specifically suited for qualitative research approaches, something that ensured that the research is on the right path in terms of scientific soundness.

In conclusion, this systematic literature review used the appropriate existing literature review following an academically sound approach, addressed the existing gap via the synthesis of the scattered information that was found and assessed the whole approach that was followed by the implementation of a tool that has been proven to be one that is very suitable for qualitative research.

4.8. Research Limitations

This systematic literature review’s limitations had to do with the following:

• Time and resource limitations, as the author had at his disposal a specific number of resources and strict deadlines to follow, something that probably has decreased, e.g., the number of articles that were scrutinized, etc.
• The availability of a quite a limited number of published papers since the topic is quite novel and the available papers were scattered under different topics, something that made their gathering quite challenging.
• The fact that only papers that were published in the English language were used for this systematic literature review, something that might have decreased the final number of the scrutinized published peer reviewed papers.

4.9. Conclusions

This research is mainly focused on the use of micro fulfilment centers in urban areas and via a rigorous, scientifically correct methodology tries to underline their importance in alleviating the urban last mile logistics problem by replacing traditional approaches, like the use of warehouses and distribution centers in the perimeters of the cities, etc. in a way that it will also enhance the triple bottom line of the urban last mile logistics.

In an urbanized world in which swift delivery is already not a trend, but instead the norm, retailers try to stay competitive and at the same time, sustainable. In their efforts towards that direction, they can find a very powerful ally in the use of micro fulfilment centers. The limited and highly costly space in urban areas makes the use of micro fulfilment centers, especially in the center of the cities, imperative. Their implementation in combination with the use of new technologies in picking, packing, order fulfilment and delivery (e.g., use of drones, A.I. in optimize routing, robots and electric or unmanned vehicles), can alleviate the urban last mile logistics problems as it can contribute in a positive way to lowering CO₂ emissions and traffic congestion, increasing customer satisfaction and decreasing delivery costs, and thus, it can have a positive sustainable impact that can benefit retailers, logistics providers and citizens. Such benefits make the use of micro fulfillment centers, especially in city centers, a very sustainable solution, which can have a very positive impact in alleviating the urban last mile logistics problem as well.