4.2.1. Equipment

Wood and Gidado [50] suggested that the definition of a complex project should refer to the interaction, interdependencies, and interrelationships between the parts of a project and that a great deal of complexity lies within the organizational aspects of a project. The dynamics of innovation are based upon a wide spectrum of possibilities within the system, including incremental innovation at one extreme and breakthrough innovation at the other. Innovation is a process whereby the learning experience and the technologyadoption life cycle contribute to the creative thinking behind underlying motivational forces, whether technology- or market-driven [51]. When it comes to maintenance adequacy, the main objective is to provide maintenance capacity (resources) to meet the random maintenance workload, in order to achieve several objectives that include maximizing the system availability, safety, and the utilization of limited resources [52]. The area of asset management is gaining significance, especially in the availability contracts [53]. Maintaining a proper fleet of equipment can be of strategic importance to a company in cases where the award of a contract is also based upon the condition and availability of the equipment [54]. Furthermore, any unavailability of the proper equipment could cause its overturning, causing damage to property and personnel injury or even fatality, as Edwards [55] highlights.

According to the above literature review framework concerning equipment-related factors that affect the operator's productivity, the AHP analysis revealed the trends depicted in Figure 9.

**Figure 9.** Equipment sub-criteria scoring.

Fleet availability and maintenance adequacy were of great interest for most of the evaluators, and they presented similar weighting results. Specifically, equipment operators granted 12% and 11% to fleet availability and maintenance adequacy, respectively, declaring those two factors as the most influential ones when it comes to construction equipment.

#### 4.2.2. Operator's Competence

The research suggests that personal motivation is a critical internal driving force that, if harnessed, can significantly improve an operator's productivity rate when working mobile plant and machinery [56]. Edwards et al. [56] concluded that the operators' personal motivation can best be encouraged by paying attention to "personal satisfiers" and "security" aspects, with particular emphasis being given to work flexibility and variety, a safe work environment, and appropriate operator remuneration.

In terms of reducing fuel consumption, unit emissions and cost, Jukic and Carmichael [57] revealed that, compared to the baseline values, trained drivers saw a reduction in their fuel consumption by an average of 8.5 percent, reducing to 7.7 percent in the several weeks following training.

Regarding the operator's knowledge/experience, Edwards [58] indicated that the more competent (a mix of qualification and experience) an excavator operator is, the more efficiently (i.e., productively) they can employ the machine and vice versa.

Fatigue is one of the factors leading to reduction in productivity, poor quality of work, and increased risk of accidents in construction [59]. Handling heavy construction equipment is considered as a hazardous occupation and requires personnel to maintain high levels of work situational awareness (WSA). In an analysis made by Sneddon et al. [60], it was found that higher levels of stress, sleep disruption, and fatigue were significantly associated with lower levels of WSA.

The AHP results highlighted the aforementioned factors against the operator's competence among evaluators, as shown in Figure 10.

**Figure 10.** Operator's competence sub-criteria scoring.

The AHP weighting results point out the knowledge/experience criterion as being the most influential on the operator's competence, with total scores of 31% and 21% for the operator and the equipment owner evaluation groups, respectively.

#### 4.2.3. Task

According to Dinakar [61], a clean and efficient planning mechanism, which clearly specifies the work and timetable to be used, can prevent delays in construction projects. Particularly in the European Union, it is a common practice to execute most of the public works through co-founded financial projects. Those projects are characterized by tight budgets and strict timetables [62]. Such timetables could be stressful for the earthwork equipment operators, causing their productivity degradation.

Wood and Gidado [50] tried to provide a greater understanding of the science of complexity in construction. Their research results suggested that the definition of a complex project should refer to the interaction, the interdependencies, and the interrelationships

between parts of a project and that the largest amount of complexity lies within the organizational aspects of a project.

Izetbegovi´c and Nahod [63] examined the relationship between the workload, the time pressure, and the work productivity of a construction project. Their findings showed a significant productivity reduction in the case of an additional workload, no matter whether the additional work was required or was a consequence of prior poor performance.

Choi et al. [64] examined the relationship between the construction worker's occupational safety and the application of wearable devices for localization. Their research was motivated by the increasingly demanding and hazardous construction environment. Additionally, Barlow [65] raised concerns about the poor performance of the construction industry, in the UK and elsewhere, caused by increasingly demanding customers and construction project complexity.

The above factors related to the project's tasks were weighted in relation to the construction equipment operator's performance, and the AHP results are presented in Figure 11.

**Figure 11.** Task sub-criteria scoring.

The AHP results highlight the importance of the projects timetable from the project managers and the academia perspective by giving a weighting score of 14% and 7%, respectively. The weighting scores of the equipment owner and the operators point out that the project's timetable is of less importance (2% each), while their attention falls onto the project's demanding conditions (5% and 4%, respectively).

#### 4.2.4. Natural/Environmental Factors

According to the World Health Organization (WHO), hearing loss is one of the top 10 most serious health problems worldwide, and noise-induced hearing loss (NIHL) is the leading occupational disease [66,67]. Duffy et al. [68] determined the factors associated with sun exposure behaviors among Operating Engineers (heavy equipment operators), highlighting their high risk for skin cancer due to high rates of exposure to ultraviolet light and low rates of sunblock use. Additionally, Eger et al. [69] highlighted the importance of light conditions and the operator's line of sight during construction works.

The unsafe behavior that is seen everywhere on construction sites is the biggest challenge for further improvement of construction safety performance. Focusing on the "human" related issues in construction safety, Fang et al. [70] reviewed the research and practices of safety management and came up with three key elements to look at, namely safety leadership, safety culture, and safety behavior. It is also notable that the subject of construction safety in general is widely referred to in the global literature.

Elazouni and Basha [71] managed to link problems with the operating construction equipment with low productivity and noted that weather conditions are one of the main factors that are unanticipated prior to the inception of the work and adversely affect productivity.

In order to highlight the importance of soil properties during construction, Parsakho et al. [72] investigated the effects of moisture, porosity, and soil bulk density during a forest road construction. Furthermore, Devi and Palaniappan [73] presented the influence of technological, operational, and site-related parameters, such as soil properties, on the performance of earthmoving operations.

Earthwork constructions emit a large amount of dust into the environment, which causes serious health hazards to construction workers. To reveal the characteristics of the health risks to workers caused by the dust generated during the earthwork construction phase, to polish the evaluation system of health damage in construction projects, and to improve the occupational health of workers, Luo et al. [74] and Chen et al. [75] established a health-risk evaluation system, which revealed the negative effect of dust exposure to the equipment operators' performance. Additionally, Ahn and Lee [76] presented a methodology for incorporating the analysis of operational efficiency into quantifying the amount of exhaust emission from construction operations and thus pointing out the effects of those emissions on construction projects productivity.

The above factors related to natural and environmental effects were weighted in relation to the construction equipment operators' performance, and the AHP results are presented in Figure 12.

**Figure 12.** Natural/Environmental factor sub-criteria scoring.

All groups of evaluators agreed that safety conditions during construction and earthworks are of greater importance when it comes to the operator's performance. The highest score came from project managers (7%), as a result of it being their main obligation to ensure construction safety during construction works. Equipment owners (3%), academia (3%), and operators (2%) followed. On the other hand, the highest ranking given by the equipment operators was the soil properties (3%). The operators also considered that their exposure to dust and emissions had no effect on their performance.

#### 4.2.5. Relationships—Interaction

The communication channels and the relationships developed between an employer and an employee are analyzed. The manager will be considered either as an agent of the employer or as an individual actor defending his or her own interests and with the ability to intervene between the three actors [77].

In order to identify the necessary factors for a safe construction site, Mohamed [78] conducted research in which he corroborates the importance of the role of management commitment, communication, workers' involvement, attitudes, and competence, as well as supportive and supervisory environments, in achieving a positive safety climate.

Additionally, investigations have been carried out which suggest that the motivation of employees in all industries is affected by the environment or culture in which they work [79]. Their research concluded that the environment of a construction site does affect demotivation levels of site personnel. Specifically, several variables were significantly linked to this result, including long hours, chaos, non-recognition for work done, and colleagues' aggressive management style.

This study incorporates the above research to investigate the influencing weight of those relationships—interaction factors on the performance of construction equipment operators and presents them in Figure 13.

**Figure 13.** Relationships—Interaction.

The AHP results indicated the significance of the on-site communication, especially for the equipment owners, the academia group, and the equipment operators (9%, 4%, and 2%, respectively). On the other hand, what was more important for the equipment operators was the relationship between the employees and employers (2%), but also the ability to come to a solution to the problem when there is a disagreement in the field (2%). The importance of the relationship between employees and employers is also highlighted by the equipment owners (6%). The above diversity could be explained in terms of working mentality. Employees, such as the equipment operators, are the task receivers and those who are directly affected by the employer's decisions and management attitudes. The way they interact with superintendents and the way they reach a solution to a disagreement affects their psychological condition, their level of motivation and, of course, their will and temper for more productive work.

#### **5. Discussion**

It is generally accepted that construction equipment is an integral part of every project in the construction sector, and it represents a significant capital investment for the companies that own it. The efficient utilization of this resource makes the project successful [33]. This research started with the objective of identifying and hierarchizing the factors affecting the construction equipment operator's performance. This is a topic that is frequently and widely discussed in the construction industry sector, but not comprehensively examined and quantified, as was found through the literature review.

In previous research, many scholars have utilized different methods to exploit the results of other related publications, mostly by examining a project's productivity in general or in relation to other factors. However, no research has been found to systematically summarize those publications and provide a holistic approach on their interdependencies and, more specifically, to feature the linkage between equipment operator performance and the project's productivity. Two hundred and sixty-three topic-related publications were examined and visualized through the VOSViewer application. The statistical analysis of those articles revealed that the researchers' interest in construction equipment and operator productivity has been increasing over the past 5 years. Technological evolution seems to radically affect the construction sector, and therefore, it was examined as an influential factor on the construction equipment operators' performance.

The objective of this research was to identify the criteria and sub-criteria with a great effect on the equipment operator's performance. The structured interviews with experts in the field, combined with the conducted literature review led to the development of the decision tree model (Figure 6), with five main criteria affecting the operator's performance: (i) operator's competence, (ii) relationships—interaction, (iii) equipment (iv) task, and (v) natural/environmental factors. Furthermore, each criterion has been evaluated in relation to a total of twenty-one dependent sub-criteria.

The operators' competence was the most important criterion among all the groups of evaluators (i.e., academia, project managers, operators, and equipment's owners). This result supports that the idea that to ensure successful projects, an experienced and trained personnel is an important success factor. Furthermore, the availability of the equipment on the sites and the maintenance adequacy of the fleet are among the most prevailing factors between the equipment and the operator's productivity. Notably, prescriptive maintenance and the deployment of equipment are of the utmost importance according to our analysis. Regarding the task that should be delivered and to what extent this can affect the operator's performance, the academia group and the project managers highlight the importance of the project schedule, whereas the operators and equipment owners focus their attention on the project's demands. This stance discloses that the projects owners and academia demonstrate a holistic approach to the issue and not an activity-based concern, as the operators and equipment owners do. Regarding environmental factors, safety conditions are ranked first for ensuring the operator's enhanced productivity for the project managers, whereas, for the operators, soil properties are the determinant factor in their ensured work effectiveness. Lack of effective communication channels and conflicts among the construction teams are criteria that are ranked high as causal factors for an operator's poor productivity.

Based on the aforementioned research and our presented analysis, the practical applications of this study principally relate to helping stakeholders in plant and machinery to better understand the interrelationships between the factors investigated that affect the equipment operators' performance. More specifically, it offers practitioners valuable indicators to: (i) identify causal situations for the operators' inefficiencies, (ii) reinforce their fleet management, and (iii) thus ensure the project's success.
