مدل شبیه سازی برای بهینه سازی دوره امتیازی طرح مشارکت بخش دولتی و خصوصی

Public–private partnerships (PPP) are becoming an increasingly popular option of project delivery. Under the concession-based PPP arrangement, the private partner is responsible for funding the scheme, while their capital investment will be recovered through the operation revenue over the concession period. Therefore, calculating an appropriate investment return over the concession period becomes a very important aspect that influences success of the PPP project, particularly so as the concessionaire may be tempted to increase their toll/tariff should the revenue fall short of their expected. However, due to the difficulties in estimating the long-term uncertainties and wider-risk profiles at the tendering stage, the government would conduct the traditional net present value and payback period analyses to determine the concession period. In this paper, a simulation model which aims to assist the public partner to determine an optimal concession period is proposed. A hypothetical example is worked through to illustrate the concept of the simulation model. The results show that the risks and uncertainties, such as a change in inflation rate, traffic flow and operation cost, could influence the decision on the concession period. With the help of the simulation model, the impact of risk can be taken into account when establishing an ideal concession period.

There is a growing trend for governments and other clients in the construction industry to place major projects into the private sector [1]. According to Miller and Evje [2], purely public and purely private delivery mechanisms are unreliable, unstable and averse to innovation. A disparity between the desperate needs for social facilities/services and the constricted public spending has given rise to an increasing use of public–private partnerships (PPP) [3]. The PPP approach has been applied to infrastructure [4], [5] and [6], sports stadia [7] and [8], hospital [9], prison [10] and maintenance [4], [11] and [12] projects. Many studies have claimed that significant cost saving can be achieved through such an arrangement [9], [12], [13] and [14]. According to Zhang and Kumaraswamy [15], the most popular PPP option is the concession-based type such as build-own-operate-transfer in which the private partner (concessionaire) undertakes to finance, design, construct, operate and maintain the facility during a concession period that is usually determined by their public counterpart at the outset. In return, the concessionaire will recover their capital investment through the operation revenue over the concession period. Establishing an appropriate concession period is important to the success of a PPP project. Being protected by an assured minimum ‘revenue stream’, the concessionaire is entitled to raise the toll/tariff in case their actual profit falls short of the anticipated return. Projects with a shorter concession period could hence result in a higher toll/tariff regime, and this is obviously not desirable from the users’ standpoint.

PPP are becoming increasingly common and are a means of providing infrastructure without directly impacting upon a country’s public sector. In this paper, a simulation model for determining an appropriate concession period has been developed. The model can incorporate the complex impact of many different risks that could affect a PPP project. A list of deterministic and uncertain parameters which are considered essential for simulating the concession period is outlined. The deterministic parameters include the construction period (Tc), discount rate and toll/tariff regime. In contrast, the cost (Ct), operation income (It) and revenue (Rt) are considered as uncertain parameters in the simulation process. The simulation process has been illustrated through a hypothetical example. The proposed simulation model could assist the decision-makers to come up with a concession period for a PPP project that is beneficial to both sides; i.e. (i) to ensure the concessionaire could gain a reasonable rather than an excessive return, and (ii) to allow the public client to reclaim the facility at an appropriate time. The results of simulation show that by considering the minimum, expected and maximum IRR, a concession period that is less risky to the concessionaire can be identified. Furthermore, the simulation model also allows the decision-makers to establish the sensitivity of some parameters (e.g. toll/tariff regime, IRR, etc.) to the concession period and thereby providing them with a basis for negotiation. While the proposed simulation model could provide users with useful information for establishing an optimal concession period for a PPP project, further improvement may be needed to make the simulation process more practical. For instance, it may not be easy for decision-makers to accurately predict the uncertain parameters and the risk attitude of the concessionaire. Further research shall be carried out using the proposed simulation model to examine the impact of other risk factors. Besides, as it is not uncommon for appraisers to employ qualitative criteria and linguistic variables during the decision-making process, combining the quantitative results deduced from the simulation model with the fuzzy sets theory is considered to be a way forward for comprehensive proposal evaluation.