Minister of road transport and highways and shipping Nitin Gadkari will flag off international investor roadshows for the masala bond sale planned by National Highways Authority of India (NHAI) in Singapore on Monday, two people aware of the development said.Masala bonds are rupee-denominated bonds sold in offshore capital markets.“The roadshows are planned to take place over the next 15 days, starting with Singapore and will then move to Hong Kong, middle of the week and conclude in London in the second week of May.