Prime Minister Manmohan Singh today promised to come out with a complete policy on infrastructure, including regulatory and institutional framework, to make the sector attractive for private participation."In the coming weeks and months, we will finalise a framework on the remaining areas of infrastructure including policy, regulatory and institutional framework," Singh said after inaugurating a conference on infrastructure.Singh said the Planning Commission has estimated an investment requirement of Rs 14,50,000 crore for development of infrastructure by 2012."Public investment has its limitations. Unless the private sector came forward, either through participation with public sector or on its own, infrastructure would remain an area of concern," he added.