The Northstar commuter rail line had its highest monthly ridership in August, with nearly 3,300 rides a day — a 24 percent increase over August 2012.

But the empty seats are what have drawn the attention of Leigh Lenzmeier, executive director of the Northstar Corridor Development Authority.

"An empty seat is a blown marketing opportunity," said Lenzmeier, a Stearns County commissioner who hopes to extend the 41-mile line to St. Cloud. It now runs between downtown Minneapolis and Big Lake.

Northstar officials plan to meet with City Council members at each of the stops along the line — which include Elk River, the city of Ramsey, Anoka, Coon Rapids and Fridley — and discuss offering temporary free passes to residents unacquainted with the line.

Overall, Northstar ridership has grown 16.3 percent over the same period last year. Each month of 2013 has produced a record ridership for that particular month. The line opened in 2009.