1. Introduction
With the development of sustainable development theory and ecological economics theory, people began to realize the impact of logistics activities on the environment. According to ECOFYS (2010) [
1], around 15% of 2010 global greenhouse gas emissions resulted from transportation, which is one of the most important parts of logistics [
2]. And logistics becomes a main pollution sources and resource user [
3] and green logistics gains great attention among both academics and practitioners [
4] to make urban delivery more efficient and sustainable from both the operations and environmental standpoints [
5]. A logistics company’s operating strategy determines the direction of logistics activities and the impact of logistics activities on the environment.
These days, for an enterprise to remain competitive and successfully achieve their strategies basing on a green logistics system, they need to collaborate to achieve qualitative and quantitative performance advances [
6], share risks under environmental uncertainties [
7], access complementary resources [
8], reduce transaction costs [
9], enhance productivity [
10] and economic performance [
3], achieve a stronger competitive position and gain sustained market advantage [
11,
12].
Collaboration has been studied extensively since the 1980s, with a significant amount of research having focused on supply chain collaboration. Cao and Zhang [
12] examined the nature of supply chain collaboration and found that it could improve collaborative advantage and had a bottom-line influence on firm performance, which enabled the supply chain partners to achieve synergies and superior performance. Many organizations, such as Dell and Wal-Mart, have achieved mutual benefits from supply chain collaboration [
13,
14]. Multi-enterprise collaboration has also been examined. For example, Kefah [
15] developed an integrated Game Theory (GT) approach for the coordination of multi-enterprise Supply Chains (SCs) in a competitive uncertain environment. Improving the collaboration between large and small-medium enterprises in the automobile production sector has been shown to be important for the profitability and sustainability of the collaborating companies [
16]. However, there has not been a great deal of research into inter-departmental collaboration within an enterprise even though this could have a major influence on cost effectiveness and shipping time efficiency [
17,
18,
19].
In addition to this, synergy and complexity have a great impact on each other. The greater the degree of synergy among members, the more obvious synergy effects and the more complex coordination behaviors are produced [
20]. An integrated supply model was proposed to formulate the problem of consignment-store-based complex supply chain optimization [
21]. Tamás Bányai et al. demonstrated an enhanced harmony search algorithm to find the optimum make-or-buy solution of a given maintenance related supply chain complexity problem [
22] and Danping Lin et al. have taken complexity as the technical factor when they adopt Internet of Things (IOT) in the agricultural supply chain [
23].
Methods to achieve operational and supply chain integration have been suggested by drawing upon advanced enterprise information technology [
24] and employing goal congruence [
8], decision synchronization [
14], resource sharing [
13], incentive alignment and collaborative communication [
25,
26,
27]. Z.X. Guo et al. [
28] have proposed a radio frequency identification RFID-based intelligent decision support system architecture, which can easily be integrated with production decision-making as well as production and logistics operations in the supply chain. Wulan and Petrovic [
29] developed a fuzzy logic methodology with sustainable interoperability for collaborative enterprise risk identification and evaluation that could assist either the collaboration facilitator or the enterprise users. Agent technology has also been applied to manufacturing enterprise integration and vertical enterprise collaboration [
30]. The integrated scheduling problem of production and transportation operations has been emphasized to meet due dates and to reduce costs for manufacturing enterprises [
31]. Ruohomaa and Kutvonen [
32] proposed a trust management system in which autonomous enterprises separately used automation to make private trust decisions about their membership in each collaborative venture. Roberto Tadei et al. [
33] have introduced an ICT solution and integrated the e-grocery Supply Chain with a reference business model to achieve the efficiency required in the urban logistics.
Research has tended to ignore enterprise collaborative analyses when investigating the consequences of enterprise collaboration. Synergy degree evaluations, for example, can easily identify an enterprise’s collaborative state and the relationships between internal departments. When weaknesses are defined, it is easier to identify solutions to improve departmental cooperative efficiency, which in turn would improve customer demand responsiveness and service quality [
34] and realize the purification of logistics environment and make full use of logistics resources. Thus, synergy degree evaluation is a key step and is conducive to for the construction of a green logistics system. With this aim in mind, this paper applies a synergy degree evaluation to sustainable logistics enterprises to enhance supply chain collaboration. In logistics enterprises, there is a direct relationship between efficiency and collaboration as collaboration can reduce logistics costs and the negative impact of the bullwhip effect and increase service levels, market share and capacity [
35]. Collaborative freight transportation is an emerging solution to make urban good movement more efficient, competitive and sustainable of the last mile [
36]. Logistics collaboration is also required within firms from the procurement of raw materials to the delivery of products and services to end-users and to the return of slow sales and disposables [
37]. Tyan et al. [
38] claimed that a new strategy between logistics vendors and customers could be developed by applying Synergetics to transportation management. Further, developing synergy between logistics enterprises could assist them to remain competitive and sustainable across the supply chain.
However, to determine the success of the logistics activities, it is necessary to have a method that can measure the degree of synergistic collaboration [
39] at the different resource and information sharing levels as well as between two or many entities. Zhenggang et al. [
40] provided a performance measurement system for evaluating the low-carbon logistics’ sustainable and proposed strategies from the 6 perspectives to develop the logistics enterprise in China. Measuring the degree of collaboration can assist members identify their shortcomings [
41] and benchmark their current practices against the best-in-class performers [
39]. Therefore, here we propose that to accurately measure performance. There needs to be objective measures, subjective measures, as well as a consideration of the facility and equipment elements. The objective measures allow for an analysis of the degree of compact from upstream to downstream, the departmental abilities and the state stability for each service in terms of personnel development and equipment.
This research introduces Synergetics to comprehensively evaluate the synergistic degree in sustainable logistics enterprises based on the Law of Factors of Production. The main contribution of this paper is to propose a measurement model and framework to assess the synergy degree in logistics enterprises, which is an integrated strategy that realizes economic development, resource conservation and environmental protection. Thirty order parameters from seven aspects of the logistics enterprises are selected to establish the evaluation index system.
The remainder of this paper is organized as follows. The basic principles behind Synergetics, literature review of Synergetics and a Synergetics applicability analysis for the evaluation of synergy degree in sustainable logistics enterprises are presented in
Section 2. The synergy elements and content analysis for the logistics enterprises based on the Law of Factors of Production are given in
Section 3.
Section 4 presents the measurement model and framework and a case study is conducted to evaluate the effectiveness of proposed model in
Section 5.
Section 6 gives the conclusions and future research directions.
3. Synergy Elements and Synergy Content Analysis
Based on the theory of the three productivity factors, this paper divides the sustainable logistics enterprise elements into three standards: laborers, labor objects and labor tools. Logistics enterprises establish cooperative relationships with upstream and downstream enterprises and then integrate the material resources of these enterprises to provide their logistics services. The laborers standard refers to the logistics enterprises and their related cooperative enterprises, the labor objects standard refers to the products and services offered by the logistics enterprises and the labor tools standard refers to the facilities and equipment that need to be integrated by the enterprises. In this paper, the laborers are the subject elements of the logistics enterprises’ synergistic elements, the labor objects are the object elements and the labor tools are the facility and equipment elements. In actual operations, logistics enterprises have seamless connections with the logistics links through mutual cooperation and information and resource sharing. Synergy involves four main aspects: (1) synergy between the subject, object and facility and equipment elements; (2) synergy within the subject elements; (3) synergy within the object elements; and (4) synergy within the facility and equipment elements.
3.1. Synergy between the Subject, Object and Facility and Equipment Elements
The main operating body of the logistics enterprise involves the enterprise itself as well as the upstream and downstream cooperative enterprises. On the one hand, the spatial distribution determines the route, direction and process of the logistics service for the transportation products; however, at the same time, while the cooperative mode between the subjects significantly affects the operational efficiency, a reasonably operating system enables the facilities to efficiently operate and quickly respond. On the other hand, the facilities and equipment should match with the main body and object of the enterprise to ensure an optimal allocation of resources; therefore, the synergy between the subject, object and facility and equipment elements assist the logistics enterprises to achieve high profit, high efficiency and high quality.
3.2. Synergy within the Subject Elements
Synergy within the subject elements refers to an effective collaboration between the supplier, manufacturer, wholesalers and retailers. Coordination and cooperation between the subjects from the source of production to the retailers and wholesalers can ensure that the product is always in the controllable environment necessary to maintain quality. To realize synergy within the subject elements, logistics companies need to develop a series of plans that cover such elements as the collaboration, the framework agreements, the logistics processes and the technological applications. Synergy within the subject elements not only helps to reduce logistics costs but also promotes the rapid and effective transfer of products from the upstream enterprises to the downstream enterprises.
3.3. Synergy within the Object Elements
Object elements are the logistics enterprise products that provide the logistics services. Therefore, the purpose of the logistics enterprise object element collaboration is to meet the transportation conditions, storage conditions (such as temperature and pressure, etc.) and timeliness conditions (such as shelf life restrictions). Therefore, to maintain product value, the shorter the logistics time, the higher the logistics efficiency and the lower the corresponding logistics costs.
3.4. Synergy within the Facility and Equipment Elements
Logistics enterprise operations require multiple resources such as human resources, transportation resources, storage resources and logistics information resources; therefore, effective resource collaboration helps to improve the operational level of the enterprises. The logistics enterprise completes the product’s operational logistics through the utilization of transportation equipment, storage equipment and other resources to effectively satisfy the service demands of the upstream and downstream enterprises. Therefore, transportation and storage equipment synergy is not only beneficial to effective equipment utilization but can also reduce ineffective equipment inputs to transportation and storage. Facilities and equipment collaboration is also closely related to personnel operations and the application of information technology; that is, inventory management, transportation planning and automatic inventory replenishment in logistics enterprises cannot be realized without the support of information technology. Therefore, facilities and equipment synergy can improve the overall synergy and operational efficiency. The specific synergy elements and content are shown in
Figure 2 and
Figure 3.
4. Measurement Model for Synergy Degree
It is assumed that the logistics enterprises’ subject elements, object elements and facility and equipment elements are respectively
and the jet order parameter for the collaborative elements
is
. From the positive and negative order parameters and the synergy degree
of the order parameter
for the synergy elements,
at a certain point in time
can be calculated as follows [
52];
where
is the value of the order parameter
at time
.
and
are the maximum and minimum values for the order parameter
. The greater the value of
, the higher the synergy degree between the order parameter
and the synergy element
. A linear weighted sum method is used to calculate the synergy degree
of the logistics enterprises at time
[
52]:
where
is to the
jth weight of synergy element
. The greater the value of
, the higher the synergy degree
at time
. The initial time
is given and relative to
, the total synergy degree of the logistics enterprises at time
can be calculated using the following equations [
53]:
where
is the synergy degree at time
that is relative to the initial time
. When
is positive, this indicates that the enterprise is has a cooperative development status through the interaction of the various synergy elements. The greater the value of
, the better the overall coordination of the logistics enterprises and the stronger the overall competitiveness of the enterprises. Conversely, the smaller the value of
, the lower the synergy degree. When
is negative, this indicates that at least one of the three synergy elements is developing in the direction of disorder. Compared with the initial time
, the enterprise is in a non-cooperative development stage. As
is the synergy decision function, only when is satisfied, is the synergy degree positive.
To measure the synergy degree, first, to avoid a comparison of the data at different levels and dimensions, a standard deviation formula is adopted to deal with the order parameters of each synergy element, the formula for which is as follows:
where
is the average of
at all the points in the measurement time and
is the sample standard deviation for synergy element
.
Second, the order parameter weights are calculated using the correlation coefficient method. The weights reflect the influence of the order parameters, with the greater the absolute value of the correlation coefficient between the order parameters, the higher the degree of interaction and the greater the weight. Finally, the synergy degree is measured by taking the standardized data and weights into the evaluation model. The measurement framework for the synergy degree for the logistics enterprises is shown in the following
Figure 4.