. lower average terminal dwell time improves asset utilization and service . average terminal dwell time improved slightly in 2009 compared to 2008 and improved 1% ( 1 % ) in 2008 versus 2007 . lower volumes combined with initiatives to more timely deliver rail cars to our interchange partners and customers improved dwell time in both periods . gross and revenue ton-miles 2013 gross ton-miles are calculated by multiplying the weight of loaded and empty freight cars by the number of miles hauled