1. Introduction
The organization and execution mode of urban logistics have changed dramatically with the continued development of the sharing economy [
1,
2] and progress in information and communication technology [
3]. Crowd logistics have emerged as a new logistics organization mode, and become widely adopted in urban logistics [
4]. More and more logistics enterprises are outsourcing packages to a growing number of people via online platforms [
5,
6]. Crowd logistics has gradually become an essential solution to the last-mile delivery challenges in cities [
7,
8], growing rapidly around the world. Sweden’s MyWays [
9], Flexe and TaskRabbit in the USA [
9], and China’s JD-dada, 51 Delivery, FlashEx, and Renren Express [
10] are some of the most prominent crowd logistics companies, with huge customer and participant bases. For example, as of 2019, the crowdsourcing business of Renren Express covered 92 cities, serving nearly two million merchants, and having more than ten million individual users in China [
11]. In terms of sustainability within logistics more generally, Purhejazy et al. [
12] used data envelopment analysis to compare different configurations within supply chain management and their relative resilience. The present study contributes to improving our understanding of one aspect of this system, the use of crowdsourcing to tackle the last-mile delivery challenge.
In crowd logistics, the delivery task is outsourced by the employer to an indefinite group of individuals through the online platform, who then use their underutilized vehicles to make timely deliveries to customers’ locations [
7]. Based on the concept of sharing, crowd logistics plays a vital role in enhancing the sustainability of urban logistics [
3,
13,
14] and has become a major focus for research on tackling the problem of last-mile delivery in cities [
13]. By using crowdsourcing, the emissions of pollutants, such as nitrogen oxides, PM2.5, and PM10 from cargo trucks, can be reduced by about 55% [
13]. Research has also shown that crowd logistics can reduce the pressure on the urban transportation system, improve the distribution efficiency of urban logistics, and cut down carbon emissions [
9,
14,
15,
16]. In addition, Melo and Macharis have proposed that crowd logistics could provide benefits for all stakeholders in the last-mile delivery process (e.g., better services for customers, additional revenue for crowdsourcing operators, and profits for platform providers) [
15]. Crowd workers can also get monetary rewards and experience enjoyment of work in the process of participation [
9,
17,
18].
However, even with the numerous advantages of crowd logistics, many operational problems still exist [
3,
19]. One of the significant challenges is how to get more people to participate in crowd logistics and maintain the motivation to participate among crowd workers [
18,
20,
21]. Key reasons that seem likely to decrease the willingness of crowd workers to participate in crowd logistics include: (1) crowd logistics is still in the exploration stage, facing a number of management, technical and legal challenges [
19]; (2) monetary reward alone may not be enough to motivate continued participation of crowd workers [
22]; (3) the time, energy and equipment costs incurred by the crowd workers may discourage continued participation [
9,
23]; and (4) risks and safety issues caused by delays in delivery, loss or damage to goods, and traffic accidents may reduce trust between the crowd workers and employer (or platform) [
3,
18,
24]. Resolving the problems that may depress participation in crowdsourcing has become a critical issue in the field of logistics research.
Most of the current studies on this issue have focused mainly on concepts (e.g., Mladenow et al., 2015 [
3]; Mladenow et al., 2016 [
9]; Carbone et al., 2017 [
24]) and on the simulation stage (e.g., Chen and Chankov, 2017 [
7]; Arslan et al., 2019 [
25]), and lack empirical analysis from the perspective of crowd workers [
14,
18], crowdsourcing communities [
26], and leader support [
27]. To address this knowledge gap, we reviewed the literature to construct a Push–Pull–Mooring (PPM) theoretical model of the factors affecting the willingness and continued participation of crowd logistics workers. This study contributes to the crowd logistics literature by examining the motivations affecting the continued participation among crowd workers. We modeled and tested the influences of the push, pull, and mooring factors and explored the mediating role of trust in the process, contributing to the application of PPM theory to a wider range of phenomena. Our study provides insights into how crowd logistics platforms might best attract, motivate and retain crowd workers.
The rest of this paper is arranged as follows: the second section presents the literature review; the third section analyzes the theoretical background, constructs the theoretical model, and puts forward the research hypothesis; the fourth section presents the research method and empirical results; the fifth section discusses the theoretical implications and practical implications of the study, and proposes some recommendations; and, finally, the sixth section presents the conclusion.
3. Theoretical Model and Hypothesis
3.1. PPM Theory
The use of Push–Pull–Mooring (PPM) frameworks originates in the field of demography, where they have been used to model population migration [
39,
40,
41] by capturing the influencing factors and motivations for people to move from one place to another over a period of time [
40]. As shown in
Figure 1, the theory mainly consists of three aspects [
41]:
(1) Negative push factors from the origin, such as inconvenient transportation, drought, backward education, and war;
(2) Positive pull factors from the destination, such as pleasant climate, convenient transportation, developed economy, advanced education, and abundant freshwater resources; and,
(3) Constraints or facilitation factors from individuals and society, i.e., mooring factors, such as previous migration experience, migration cost, and migration security.
PPM theory has subsequently been applied in various disciplines. Tang et al. [
42], for example, studied the factors influencing online shopping behavior from Personal Computer (PC) terminals to mobile intelligent devices using PPM Theory. Leng [
43] used a PPM model to examine consumer switching behavior with regard to their mobile service providers. Jung et al. [
39] tested the applicability of the theoretical model in traveler route selection and used it to analyze tourists’ switching behavior. Bin et al. employed this theory in studying the influencing factors among enterprises implementing crowd logistics [
44].
Furthermore, PPM theory explains the process of shifting from a poor environment to a better and more sustainable one. This is exactly in line with the problems encountered by current crowd logistics platforms. More specifically, crowd logistics platforms need to overcome the difficulty of motivating crowd workers to continue participating in crowd logistics. In this way, the sustainable operation of crowd logistics in the city can be better guaranteed.
Therefore, building on these previous studies and the relationship between theory and practice, we used the PPM theory as a framework for examining the factors affecting crowd workers’ continued involvement in crowd logistics.
3.2. Research Model Construction
We applied PPM theory to group the factors influencing crowd workers’ continued participation in crowd logistics into push, pull and mooring factors. The research model is shown in
Figure 2. The model thus identifies six factors that are hypothesized to directly affect crowd workers’ intention to continue participating in crowd logistics. In addition, we hypothesized, following Ye and Kankanhalli [
18], that appropriate monetary rewards will enhance trust.
3.3. Hypothesis
This paper proposes several research hypotheses based on the three PPM aspects (push, pull, and mooring) and analyzed the specific factors that affect crowd workers’ continued intentions to participate in crowd logistics. Push factors include flexibility and enjoyment from the previous job, pull factors include monetary rewards and entry barriers for work, while mooring factors include trust and the cost of participation.
3.3.1. Push Factors
Push factors mainly refer to the unfavorable and tedious aspects of the crowd workers’ previous work. These negative factors drive crowd workers to continue participating in crowd logistics instead of returning to their previous jobs. In this study, the push factors include flexibility in the previous job and the enjoyment acquired from the previous job.
(1) Previous job flexibility
Studies show that job flexibility provides employees with balance and leisure, thereby increasing their work efficiency [
45]. As a result, more and more companies have realized they can achieve sustained growth through flexible work schedules, particularly in the face of a tight labor market, an aging labor force, and excessive reliance on employees [
46]. The need for flexibility is very relevant for participants of crowd logistics. But understanding how it affects people’s motivations to remain on the platform requires further exploration. Previous studies have identified autonomy and flexibility as important reasons for people to leave their work and switch to crowd logistics [
9,
18,
35]. In many cases, crowd workers’ previous work (especially for those with full-time jobs) afforded limited flexibility in terms of work, coordination of work and family affairs, and self-motivation [
47]. Based on these arguments, we propose the following hypothesis:
H1: The lower the work flexibility of crowd workers’ previous jobs, the stronger their intention to continue participating in crowd logistics.
(2) Previous job enjoyment
Crowd logistics, with its novel operation mode, unique delivery experience, and unconstrained working atmosphere, can provide additional enjoyment to crowd workers [
37]. Since participation is on a voluntary basis, crowd workers can choose the logistics task(s) they wish to perform [
9,
48]. When the difficulty of the task matches one’s ability, the crowd worker can complete the task with confidence and enjoy the process [
49]. Other jobs (e.g., full-time, part-time and independent short-term contracts) may not be as flexible and autonomous as crowd logistics. In those work environments, tasks beyond the worker’s personal abilities can cause anxiety and stress, which can subsequently result in job burnout [
37]. Hence, we propose the following hypothesis:
H2: The lower the enjoyment of crowd workers’ previous jobs, the stronger their intention to continue participating in crowd logistics.
3.3.2. Mooring Factors
Mooring factors mainly refer to elements that hinder or promote crowd workers’ continued participation in crowd logistics. The mooring factors in this paper include the trust between the crowd worker and the platform (crowdsourcer) and the cost of participation.
(1) Trust
Trust can be earned when the platform (crowdsourcer) evaluates the crowd workers’ solutions and rewards their work fairly [
18], which could then serve as the basis for effective cooperation [
50]. Previous studies have shown that trust is a vital factor that can influence crowd workers’ participation in crowdsourcing [
18,
22]. It affects crowd workers’ behavior and decision-making processes [
51]. For example, a study by Shen et al. [
26] found a person with a high level of trust in other Wikipedia contributors would be more likely to contribute to the community. However, due to potential risks in crowd logistics (e.g., delivery delays, extra costs, unclear distribution of responsibilities) [
3] and inherent vulnerabilities in online activities [
52], more effort is required to establish trust between the crowd worker and the platform (crowdsourcer). Therefore, we assume greater trust would encourage the crowd worker to continue in his/her participation in crowd logistics while facing potential risks. We propose the following hypothesis:
H3: The higher the trust between the crowd worker and the platform (crowdsourcer), the stronger the crowd worker’s intention to continue participating in crowd logistics.
(2) Costs of participation
When the crowd worker participates in crowdsourcing activities, certain costs would inevitably be incurred [
23]. These costs include money expenditure, time, and mental effort [
53]. When a crowd worker participates in crowd logistics, he or she needs to provide transportation and learn the method of operation of the delivery software. Moreover, in order to provide customers with a more satisfactory service, the crowd worker would need to spend time and energy on training and practice. Since crowd logistics is still in its infancy [
9], the existence of potential risks could indirectly increase costs for continued participation. Previous studies have shown that knowledge sharing could be viewed negatively as losing the knowledgeability edge and discourage individuals from future exchanges [
18,
54]. Based on these arguments, we propose the following hypothesis:
H4: The higher the participation cost, the lower the crowd worker’s intention to continue participating in crowd logistics.
3.3.3. Pull Factors
Pull factors refer to the positive and favorable factors in crowd logistics that encourage continued participation. In this study, the pull factors considered include monetary rewards and entry barriers for work.
(1) Monetary rewards
Studies have shown that for crowd logistics, external incentives serve as crucial driving factors for crowd workers’ continued participation [
9,
37]. For instance, people may use their spare time to participate in crowd logistics in order to get additional income [
37]. While money is not the only reason for crowd workers to engage in crowdsourcing, financial incentives are undeniably significant [
32,
55]. Due to the importance of monetary rewards in motivating people, some of the main challenges facing crowdsourcing platforms are related to finances, such as reasonable pricing, salary plans, and effective task allocation [
56]. Crowdsourcing platforms need to provide the most appropriate compensation solution to encourage the continued participation of crowd workers [
57]. Thus, monetary incentives are likely to be significant for the continued participation of crowd workers in crowd logistics and propose the following hypothesis:
H5: Monetary reward is positively correlated with crowd workers’ continued participation in crowd logistics.
(2) Entry barriers for work
Since participation in crowdsourcing is voluntary and selective [
3,
6,
48], crowd workers can have direct access to the job. As some scholars have pointed out, crowd workers can be self-employed, freelancers, or even unemployed [
4,
9]. In crowd logistics, as long as the crowd worker is familiar with operating a smartphone and is willing to spend a certain amount of time and energy, they can participate in the delivery. Unlike full-time logistics staff, crowd workers can participate in crowd logistics without having to undergo interviews, which provides them some degree of freedom and flexibility [
18]. Based on these arguments, we propose the following hypothesis:
H6: Entry barriers for work are negatively correlated with crowd workers’ continued participation in crowd logistics.
(3) The mediating effect of trust between monetary reward and crowd workers’ continued participation
We predicted above that trust and monetary rewards will both have direct effects on crowd workers’ continued participation in crowd logistics. Monetary rewards also have an indirect effect, in that workers’ perception of fair compensation serves to increase their trust in the crowdsourcing platform [
22,
58], which, in turn, is likely to increase their participation intention. Crowd workers who do not feel they receive fair and equitable remuneration may show low-trust behavior and reduced willingness to participate [
18]. Based on these arguments, we argue that trust between the crowd worker and the platform has a positive mediating effect on the monetary reward and propose the following hypothesis:
H7: The impact of monetary reward on crowd workers’ continued participation within crowd logistics will be greater when trust in the platform is higher.
6. Conclusions
The emergence and rapid growth of crowd logistics represents an important response to the last-mile delivery challenge, which makes the continued participation of crowd workers a key issue in today’s logistics industry. However, motivating continued participation in crowd logistics has some challenges, which could worsen if these issues are not addressed. In order to understand the underlying factors behind crowd workers’ motivations, we developed and implemented a new model based on the Push–Pull–Mooring theory. Our empirical results show monetary rewards and trust are strongly and positively correlated with continued participation in crowd logistics, while enjoyment from previous work and entry barriers have a significant negative correlation. Trust has a mediating effect on how monetary incentives influence crowd workers’ willingness to continue working in crowd logistics. The findings of this study contribute to the growing literature on crowd logistics.
Based on the findings of this study, we recommend that crowd logistics platforms should offer reasonable monetary incentives and keep these under constant review, build a high degree of trust and cooperation with their crowd workers, and initiate activities geared towards promoting satisfaction at work. The recommendations based on the results of this study can help crowd logistics platforms formulate suitable policies and implement measures that would encourage continued participation in crowd logistics.
However, we should acknowledge that our study has some limitations. First, the survey data comes from an urban agglomeration in South Central China, the characteristics of which may be very different from other settings. This is a challenge for all studies of crowd logistics, as geographical location is obviously a significant influence on how crowd logistics operate on the ground. It would, therefore, be necessary to conduct further studies for different regions and countries to compare with the results of this study. Second, many of our participants were in low-income jobs, with one-third of them being unemployed. We cannot know if this is typical of crowd logistics workers, though it seems possible; clearly, further research is required. Although there is a body of research developing on crowd workers generally, the demographic profile of such workers is likely to be very diverse, and logically each type of crowdsourced work may attract a different demographic, reflecting the differing expertise involved and the different entry barriers. The research on crowd logistics is still in its infancy, and research on many other aspects regarding crowd workers, platforms, consumers, and related enterprises are needed to support the sustainable development of the crowd logistics industry.