{"pre_text": ["our environmental site activity was as follows : 2013 2012 2011 ."], "post_text": ["the environmental liability includes future costs for remediation and restoration of sites , as well as ongoing monitoring costs , but excludes any anticipated recoveries from third parties .", "cost estimates are based on information available for each site , financial viability of other potentially responsible parties , and existing technology , laws , and regulations .", "the ultimate liability for remediation is difficult to determine because of the number of potentially responsible parties , site-specific cost sharing arrangements with other potentially responsible parties , the degree of contamination by various wastes , the scarcity and quality of volumetric data related to many of the sites , and the speculative nature of remediation costs .", "estimates of liability may vary over time due to changes in federal , state , and local laws governing environmental remediation .", "current obligations are not expected to have a material adverse effect on our consolidated results of operations , financial condition , or liquidity .", "property and depreciation 2013 our railroad operations are highly capital intensive , and our large base of homogeneous , network-type assets turns over on a continuous basis .", "each year we develop a capital program for the replacement of assets and for the acquisition or construction of assets that enable us to enhance our operations or provide new service offerings to customers .", "assets purchased or constructed throughout the year are capitalized if they meet applicable minimum units of property criteria .", "properties and equipment are carried at cost and are depreciated on a straight-line basis over their estimated service lives , which are measured in years , except for rail in high-density traffic corridors ( i.e. , all rail lines except for those subject to abandonment , yard and switching tracks , and electronic yards ) for which lives are measured in millions of gross tons per mile of track .", "we use the group method of depreciation in which all items with similar characteristics , use , and expected lives are grouped together in asset classes , and are depreciated using composite depreciation rates .", "the group method of depreciation treats each asset class as a pool of resources , not as singular items .", "we currently have more than 60 depreciable asset classes , and we may increase or decrease the number of asset classes due to changes in technology , asset strategies , or other factors .", "we determine the estimated service lives of depreciable railroad property by means of depreciation studies .", "we perform depreciation studies at least every three years for equipment and every six years for track assets ( i.e. , rail and other track material , ties , and ballast ) and other road property .", "our depreciation studies take into account the following factors : f0b7 statistical analysis of historical patterns of use and retirements of each of our asset classes ; f0b7 evaluation of any expected changes in current operations and the outlook for continued use of the assets ; f0b7 evaluation of technological advances and changes to maintenance practices ; and f0b7 expected salvage to be received upon retirement .", "for rail in high-density traffic corridors , we measure estimated service lives in millions of gross tons per mile of track .", "it has been our experience that the lives of rail in high-density traffic corridors are closely correlated to usage ( i.e. , the amount of weight carried over the rail ) .", "the service lives also vary based on rail weight , rail condition ( e.g. , new or secondhand ) , and rail type ( e.g. , straight or curve ) .", "our depreciation studies for rail in high density traffic corridors consider each of these factors in determining the estimated service lives .", "for rail in high-density traffic corridors , we calculate depreciation rates annually by dividing the number of gross ton-miles carried over the rail ( i.e. , the weight of loaded and empty freight cars , locomotives and maintenance of way equipment transported over the rail ) by the estimated service lives of the rail measured in millions of gross tons per mile .", "rail in high-density traffic corridors accounts for approximately 70 percent of the historical cost of rail and other track material .", "based on the number of gross ton-miles carried over our rail in high density traffic corridors during 2013 , the estimated service lives of the majority of this rail ranged from approximately 15 years to approximately 30 years .", "for all other depreciable assets , we compute depreciation based on the estimated service lives ."], "table": [["", "2013", "2012", "2011"], ["open sites beginning balance", "284", "285", "294"], ["new sites", "41", "56", "51"], ["closed sites", "-57 ( 57 )", "-57 ( 57 )", "-60 ( 60 )"], ["open sites ending balance atdecember 31", "268", "284", "285"]], "table_ori": [["", "<i>2013</i>", "<i>2012</i>", "<i>2011</i>"], ["Open sites, beginning balance", "284", "285", "294"], ["New sites", "41", "56", "51"], ["Closed sites", "(57)", "(57)", "(60)"], ["Open sites, ending balance atDecember 31", "268", "284", "285"]]}

Question: what was the net change in the number of environmental sites from 2012 to 2013?
Evidence:
table_4: the open sites ending balance atdecember 31 of 2013 is 268 ; the open sites ending balance atdecember 31 of 2012 is 284 ; the open sites ending balance atdecember 31 of 2011 is 285 ;
Program: subtract(268, 284)
Answer:
str_answer: -16
exe_answer: -16