Resalat Tunnel is one of the widest twin-tube traffic tunnels of its kind, located in the heart of Tehran. Traffic volume passing through this tunnel is so that congestion exists in most hours of the days, particularly in rush hours time. Therefore the design of ventilation system for these tunnels is of paramount importance for all of tunnel users. All type of ventilation systems were technically and economically examined for these tunnels and finally the longitudinal type was selected as the best choice. The number and type of jet fans and arrangement of these fans in the tunnels were considered.