یک مدل برای تعیین طول عمر پروژه و دوره تضمین پروژه های BOT  A model for determining the optimal project life span and concession period of BOT projects

1. Introduction The public sector is traditionally responsible for infrastructure development within its jurisdiction and is the sole financer of the projects involved. However, this form of procurement is becoming increasingly outdated due to a perceived over-reliance on public finance, soft budget constraints, deficiencies in managing financial risks, lack of user responsibility and inefficiencies in the construction and operation processes. It is against this backdrop that, since the 1980s, the private sectors of Western nations are increasingly participating in infrastructure development (Delorme et al., 1999; Bao, 2009). The build-operate-transfer (BOT) contractual arrangement is today an important example of such participation. Here, the government provides the private investor/concessionaire with the specific concession period (for brevity, the terms ‘private investors’ and ‘concessionaire’ are used interchangeably). This period, termed the transfer point, is purposely set to enable the concessionaire to collect revenues by operating and maintaining the infrastructure involved before its transference back to the government (Levy, 1996) at the end of the period. The BOT model, therefore, provides an effective way of utilizing private funds in the provision of public infrastructure while affording the opportunity for the use of the innovative technologies, management skills and operational efficiencies possessed by private businesses (Shen et al., 2007). The BOT approach makes an important contribution to the development of infrastructure both in developed and developing countries and a significant research effort has investigated the methods needed to help in its effective application. Most of this effort focuses on the identification and distribution of risks (e.g. Wibowo and Wilhelm Alfen, 2014), project pricing and finance arrangements (Yang and Meng, 2000; Devapriya and Pretorius, 2002), as well as sustainable organizational structures and characteristics (Lokiec and Kronenberg, 2003). Research has also been conducted on the methods and tactics involved in project financing (Smith et al., 2004) and still other studies investigating the role of government in BOT-led infrastructure development (e.g., Ye and Tiong, 2000; Kumaraswamy and Zhang, 2001; Wibowo and Wilhelm Alfen, 2014) in providing an important theoretical basis for their financing, pricing, managing and implementation.