standardized maintenance based on an industry trade publication , we operate the eighth largest vocational fleet in the united states . as of december 31 , 2014 , our average fleet age in years , by line of business , was as follows : approximate number of vehicles approximate average age .
what is the percent of the residential vehicles as part of the fleet
through standardization of core functions , we believe we can minimize variability in our maintenance processes resulting in higher vehicle quality while extending the service life of our fleet . we believe operating a more reliable , safer and efficient fleet will lower our operating costs . we have implemented standardized maintenance programs for approximately 60% ( 60 % ) of our fleet maintenance operations as of december 31 , 2014 . cash utilization strategy key components of our cash utilization strategy include increasing free cash flow and improving our return on invested capital . our definition of free cash flow , which is not a measure determined in accordance with united states generally accepted accounting principles ( u.s . gaap ) , is cash provided by operating activities less purchases of property and equipment , plus proceeds from sales of property and equipment as presented in our consolidated statements of cash flows . for a discussion and reconciliation of free cash flow , you should read the 201cfree cash flow 201d section of our management 2019s discussion and analysis of financial condition and results of operations contained in item 7 of this form 10-k . we believe free cash flow drives shareholder value and provides useful information regarding the recurring cash provided by our operations . free cash flow also demonstrates our ability to execute our cash utilization strategy , which includes investments in acquisitions and returning a majority of free cash flow to our shareholders through dividends and share repurchases . we are committed to an efficient capital structure and maintaining our investment grade credit ratings . we manage our free cash flow by ensuring that capital expenditures and operating asset levels are appropriate in light of our existing business and growth opportunities , and by closely managing our working capital , which consists primarily of accounts receivable , accounts payable , and accrued landfill and environmental costs . dividends in july 2003 , our board of directors initiated a quarterly cash dividend of $ 0.04 per share . our quarterly dividend has increased from time to time thereafter , the latest increase occurring in july 2014 to $ 0.28 per share , representing a 7.7% ( 7.7 % ) increase over that of the prior year . over the last 5 years , our dividend has increased at a compounded annual growth rate of 8.1% ( 8.1 % ) . we expect to continue paying quarterly cash dividends and may consider additional dividend increases if we believe they will enhance shareholder value . share repurchases in october 2013 , our board of directors added $ 650 million to the existing share repurchase authorization originally approved in november 2010 . from november 2010 to december 31 , 2014 , we used $ 1439.5 million to repurchase 46.6 million shares of our common stock at a weighted average cost per share of $ 30.88 . as of december 31 , 2014 , there were $ 360.2 million remaining under our share repurchase authorization . during 2015 , we expect to use our remaining authorization to repurchase more of our outstanding common stock. .