South Africa’s only high-speed rail network is drawing up a multibillion rand plan to expand outside Johannesburg and Pretoria, joining a potential bonanza of infrastructure projects the government says are key to reviving the economy. A proposal for the venture is awaiting sign-off by the National Treasury, William Dachs, chief executive officer of the Gautrain company, said in an interview. Investment and loans would come from a mix of private investors and state institutions such as the Development Bank of Southern Africa, he said.