Table: tib_cont_road
Columns: year
road_opened
road_closed
freight_carried_s_tonne
super_b_capacity_reached_citation_needed
number_of_truck_loads_north

Question: What is the smallest amount of freight carried on the road that closed on March 31 and reached super B capacity on February 17 after 2011?
SQL: SELECT MIN("freight_carried_s_tonne") FROM tib_cont_road WHERE "road_closed" = 'march 31' AND "super_b_capacity_reached_citation_needed" = 'february 17' AND "year" > 2011