St. Joseph County and South Bend have averaged modest population growth each of the past four years, but they’ve trailed the state of Indiana’s growth rate, according to recently released Census Bureau estimates. City, county and business leaders say they have a prime opportunity to change that by double-tracking part of the South Shore Line, which would eliminate the need for the passenger line to wait for oncoming freight trains, and realigning the South Shore’s approach to South Bend International Airport. They say the work, when finished in 2020, will reduce the South Bend-to-Chicago trip from its current 2.5 hours to 90 minutes, and possibly down to 75 minutes on a special limited-stop trip each weekday morning and evening.