THE man who has managed the construction and expansion of Delhi's successful metro network for the last 16 years, Dr E Sreedharan, will retire as managing director of Delhi Metro Rail Corporation (DMRC) tomorrow at the age of 79 and hand over to his chosen successor Mr Mangu Singh. Sreedharan, who joined DMRC in 1995, is a career railwayman and has been in Indian government service for 58 years.