. lower average rail car inventory reduces congestion in our yards and sidings , which increases train speed , reduces average terminal dwell time , and improves rail car utilization . average rail car inventory decreased slightly in 2011 compared to 2010 , as we continued to adjust the size of our freight car fleet . average rail car inventory decreased 3% ( 3 % ) in 2010 compared to 2009 , while we handled a 13% ( 13 % ) increase in carloads during the period compared to 2009