It is a common practice that many countries seek new ways to manage and finance their transport infrastructure projects through the formation of Public Private Partnerships (PPPs) ^[1][2][1,2]. Large transport infrastructure projects constitute capital intensive projects where the pay-back period may extent from many years to some decades ^[3][4][5][3,4,5]. Therefore, PPPs agreement leverage capitals from the private sector and share the business risks between the involved parties, ^[6][7][6,7]. Identifying the reasons for PPP contracts in transport sector, three key factors can be highlighted: (a) the project financing conditions and the capitals availability and cost for implementing the projects; (b) the agreement on performance management, governance and productivity of the project; and (c) the sharing mechanism of business incentives and risks [8].

Possibly the most common practice to apply PPPs is the concession approach, according to which the concessionaire takes over the financing, design, construction, maintenance, operation and exploitation of the infrastructure project, [9]. Therefore, the concessionaire collects the fees/fares that the users of the infrastructure pay to meet its business plan where a bottom line regarding the debt/loans coverage is well illustrated in the contact, and in many cases caps in earnings and benefits are also included for a pre-defined, contractually agreed period of time ^[7][9][10][7,9,10].

The construction of the project is taken over by the concessionaire and executed usually by the construction sector of the shareholders. Therefore, the concessionaire does not construct itself, but gives the rights and obligations in a back-to-back scheme to its shareholders, [11]. Consequently, the shareholders are becoming subcontractors at the same time. In parallel, the concessionaire has the obligation to operate and maintain the project. Once again, the maintenance of the project is executed either by the concessionaire itself or the affiliated companies [9]. Therefore, the concessionaire has to manage its subcontractors in the maintenance of the project in terms of project management, price, quality, safety, whereas (at the same time) its subcontractors are directly related with its shareholders. The obstacles are obvious, since supervising or monitoring an entity with which there is a direct relationship cannot provide a framework of independent control, ^[9][10][9,10].

Sustainability of these projects is directly linked with the conditions facing the personnel working for their construction and maintenance, as part of the society pillar including in the objectives announced by the United Nations for sustainable development [12]. Prevention of accidents at work and occupational diseases ensure a better wellbeing for the personnel working on PPP/concession projects ^[13][14][13,14]. In addition, especially regarding transportation infrastructure projects, the smooth and better operation and construction of these projects depends on management comprehensiveness over safety issues ^[15][16][15,16].

2. Occupational Health and Safety for PPP Transportation Projects 

The investigation of how the transport infrastructure operators are understanding and prioritize Occupational Health and Safety (OHS) in corporate environment and evaluate the importance of incentives and actions for improving the level of safety in operation of transport infrastructures ^[16][17][16,17]. The application is the concession projects/PPPs, referring to private sector management in public transport infrastructure, providing key messages to planners, managers, and researchers in the field of transportation and asset management ^[18][19][18,19]. By a systemic approach and by reviewing relevant literature, the key factors influencing OHS are presented thoroughly in this research. The prioritization of the key performance factors and the incentives towards efficiency and performance in the frame of OHS are reviewed by a questionnaire where the structure and the expectations in terms of outputs are analyzed. The numerical application is the Greek PPP projects that represent the 80% of the new infrastructure investments implemented in transportation sector in this state. It is noteworthy that the survey contacted to PPP project personnel that it is active in all responsibility levels of corporate hierarchy including top and operational management. Management factors such as the customization of the contracts with the subcontractors, the analysis of the occupational health and safety conditions in the design phase of the project, the clear definition of roles and responsibilities on site, but also the commitment to occupational health and safety from the top management of the company are directly contributing aspects which support the achievement of a high safety performance level in a PPP/concession project. Furthermore, the creation of the safety climate in the worksite, a smooth, comprehensive and organized flow of information, in combination with the proper staff management and site organization, can provide an adequate environment for effective project in terms of occupational health and safety. Finally, the implementation of an occupational health and safety management system along with a field and live risk management scheme provide all of the technical tools to mitigate the occupational hazards and improve the working conditions. On the other, hand, it seems that the extended level of subcontracting as well as the conditions developed due to the COVID-19 pandemic cannot be an obstacle for achieving high safety performance in PPP/concession projects. Similarly, the implementation of a system for sanctions and rewards in the worksite of PPP/concession projects does not seem to have necessarily a positive effect for the enhancement of the safety performance. The proposed survey structure and the presented statistical analysis approach addressed the correlation of OHS and management performance factors, such as learning, performance monitoring, operative risk management, and safety climate. Particularities of the concession projects/PPPs are considered and the survey analysis outputs provide key messages in a worldwide scale. The survey is addressed to both top and middle management, providing feedback from all involved responsibility actors in managing OHS, identifying best practices and key areas may need to take additional actions and measures. Finally, good practices are highlighted and key findings for the liaison between safety performance and safety management constitute input for further research are highlighted. Conventional wisdom is to present the structure for contacting a survey to evaluate the management comprehensiveness over OHS for large transport operators. The numerical application provides essential messages to compare with relevant cases in transportation, but also to other relevant industries such as energy and telecommunication. The survey results provide essential messages to planners, managers and decision makers in the transportation sector towards OHS comprehensiveness and highlight key actions towards effective safety performance.