土木工程 建筑 外文翻译 外文文献 英文文献 公路建设造价的未来.docx
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土木工程 建筑 外文翻译 外文文献 英文文献 公路建设造价的未来.docx
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土木工程建筑外文翻译外文文献英文文献公路建设造价的未来
本科生毕业设计(论文)
外文翻译
(2009届)
题目Ⅰ:
EstimatingFutureHighwayConstructionCosts
2009年2月19日
EstimatingFutureHighwayConstructionCosts
C.G.Wilmot,M.ASCE,1andG.Cheng,P.E.2
Abstract:
TheobjectiveofthisresearchwastodevelopamodelthatestimatesfuturehighwayconstructioncostsinLouisiana.Themodeldescribesoverallhighwayconstructioncostintermsofahighwayconstructioncostindex.Theindexisacompositemeasureofthecostofconstructionlabor,materials,andequipment;thecharacteristicsofcontracts;andtheenvironmentinwhichcontractsarelet.Futureconstructioncostsaredescribedintermsofpredictedindexvaluesbasedonforecastsofthepriceofconstructionlabor,materials,andequipmentandtheexpectedcontractcharacteristicsandcontractenvironments.Thecontractcharacteristicsandcontractenvironmentsthatareunderthecontrolofhighwayagencyofficials,canbemanipulatedtoreflectfuturecost-cuttingpolicies.ApplicationofthemodelinforecastingtohighwayconstructioncostsinLouisianashowsthatthemodelcloselyreplicatespastconstructioncostsfortheperiod1984–1997.Whenappliedtoforecastingfuturehighwayconstructioncosts,themodelpredictsthathighwayconstructioncostsinLouisianawilldoublebetween1998and2015.Applyingcost-cuttingpoliciesandassuminginputcostsare20%lessthananticipated,themodelestimateshighwayconstructioncostswillincreaseby75%between1998and2015.
Keywords:
Highwayconstruction;Costs;Estimation.
Introduction
StateDepartmentsofTransportationarerequiredtopreparehighwayconstructionprogramsthatdescribetheirplannedconstructionactivityintheshortterm.Thereisusuallyconsiderableinterestintheprogramfromlocalauthorities,politicians,andinterestgroups.Draftprogramsaretypicallypresentedtothepublicandtovariousagenciesatthelocal,regional,state,andfederallevelforcommentandreview.Ultimately,aprogramwillbeapprovedbythestatelegislatureandwillbecometheformalprogramofconstructionofthestateDepartmentofTransportationuntilanewprogramisdevelopedinthenextcycleafewyearslater.
Becauseindividualprojectsareofconsiderableimportancetopoliticiansandindividualinterestgroups,itiscommonthatprogressonaconstructionprogramiscloselymonitored.Anydeviationislikelytobequeried,andtheSecretaryofthestateDepartmentofTransportationoraseniorofficialinthedepartmentwilloftenhavetodefendthesituationpubliclyorinthestatelegislature.Thiscanleadtoperceptionsofincompetenceanderosionofsupportfromthelegislatureandthepublic.
Topreparereliablehighwayconstructionprograms,roadauthoritiesmusthaveaccurateestimatesoffuturefundingandprojectcosts.Whilefuturefundingisobviouslyneverknownwithagreatdealofcertainty,itisoftentheestimationofprojectcoststhatcauseupsetsintheexecutionofconstructionprograms.Inaccuratecostestimationisonesourceoferror,butanother,theescalationincostofaprojectovertime,isanothersourcedisruptiontotheprogramthatisusuallynotanticipatedandcateredfor.Typically,when
projectsarecosted,theircostsareestimatedintermsofthecurrentcostoftheproject,andthisestimateisnotadjustedfortheyearinwhichtheprojectisscheduledforimplementation.Thesecostincreasescanbesignificantandare,ofcourse,cumulativeacrossprojects;also,theyriseatanincreasingrateeachyearintothefuture.Estimatingfuturehighwayconstructionisthefocusofthispaper.ThemodeldevelopedinthisstudywasdevelopedwithdatafromtheLouisianaDepartmentofTransportationandDevelopment~DOTD!
andisthereforeparticulartothatstate.However,themethodologyemployedcouldbeemployedinotherareas.
MeasuringProjectCosts
Whenconstructioninthefieldlagsbehindplannedconstructionintheconstructionprogram,itisusuallybecausetheprojectsthathavebeenconstructedhavecostmorethananticipated.Thisisnotrandomvariationofactualcostsaboutestimatedcosts,because,clearly,underestimateswouldcanceloutoverestimatesovertimeinsuchasituation.Rather,itisevidenceofaconsistentunderestimateofallprojectscollectively.Thebenefitofthisisthatitcanbemeasuredattheoveralllevel,whichismucheasiertomeasurethanattheindividualprojectlevel.
Inthepast,changeinoverallconstructioncostshasbeenmeasuredintermsofconstructionindices.Theseindicesareweightedaveragesofthecostofasetofrepresentativepayitemsovertime.Theyhavebeenusedtodisplaycosttrendsinthepast.However,thereisnoreasonwhycostindicesmustberestrictedtodisplayingpasttrends;theycanalsoportrayfutureoverallcosts,providedtherepresentativepayitemsonwhichtheindexisbasedcanbeforecast.Apredictiveconstructioncostindexwasadoptedinthisstudytodescribethechangeinoverallconstructioncostsinthefuture.Theformulationoftheindexisdescribedlaterinthepaper.
PastIncreasesinConstructionCosts
Whenthechangeinoverallconstructioncostsinthepastisobserved(asmeasuredbypopularconstructioncostindices),itisapparentthattheychangesignificantlyfromyeartoyearandthatthechangescansometimesbequiteerratic.Thecommonassumptionthatconstructioncostschangewiththerateofinflationcanleadtopoorestimatesoffutureconstructioncost.Toillustrate,theFederalHighwayAdministration’sCompositeBidPriceIndex,anindexofoverallhighwayconstructioncosts,isplottedinFig.1togetherwiththeConsumerPriceIndex(CPI),acommonexpressionofgeneralinflation.TheFHWACBPIfortheentirenationandforLouisianaaloneisplottedinthediagram.Allindiceshavebeennormalizedtoavalueof100in1987forcomparisonpurposes.Fromthediagram,itisclearthathighwayconstructioncostschangeerraticallyandevendisplaydifferentshortandlong-termtrendsfromtothoseoftheCPI.ItisalsoapparentthatconstructioncostchangesaredifferentinLouisianafromthoseinthenationasawhole.Whilenotshownhere,reviewoftheFHWACBPIfromotherstatesshowsthatmanyofthemshowadeviationfromnationalvalues.
PastMethodsofForecastingHighwayConstructionCost
Forecastingfuturehighwayconstructioncostshasbeenachievedinbasicallythreewaysinthepast.First,
unitratesofconstructionsuchasdollarspermilebyhighwaytypehavebeenusedtoestimateconstructioncostsintheshortterm.However,thismethodhasgenerallybeenfoundtobeunreliable,becausesiteconditionssuchastopography,insitusoil,landprices,environment,andtrafficloadsvarysufficientlyfromlocationtolocationtomakeaveragepricesinaccurateestimatesofthepriceofindividualprojectsorevenofallprojectsinaparticularyear.
Second,extrapolationofpasttrends,ortime-seriesanalysis,hasbeenusedtoforecastfutureoverallconstructioncosts(Koppula1981;Hartgenetal.1997).Typically,constructioncostshavebeencollapsedintheseanalysestoasingleoverallexpressionofconstructioncostsuchastheFHWACBPIortheEngineeringNewsRecord’sBuildingConstructionIndex~ENRBCI!
orConstructionCostIndex~ENRCCI!
.However,thesetypesofmodelsareusuallyonlyusedforshort-termforecastingduetotheirrelianceonthenotionthatpastconditionsaremaintainedinthefuture.
Third,modelshavebeenestablishedthatdescribeconstructioncostsasafunctionoffactorsbelievedtoinfluenceconstructioncosts.Therelationshipbetweenconstructioncostsandthesefactorshavebeenestablishedfrompastrecordsofconstructioncosts.Typically,themodelsestablishedinthismannerhavebeenusedtoestimatethecostofindividualcontracts.Thesemodels,withtheirrelationalstructure,aretheonlymodelsexpectedtoprovidereliablelong-termestimates.Themodeldevelopedinthisstudyisofthistype.
ProposedConstructionCostModel
Itisclearthattherearenumerousfactorsthataffectconstructioncosts.However,itisstrikingthatmostconstructioncostmodelsdevelopedinthepasthaveusedonlyafewofthemanyinfluentialfactorsidentifiedabove.Onereasonforthisisthatinformationisgenerallynotavailableonmanyfactorsindatasetsusedtoestimatemodels.Anotherreasonisthatinformationonthequalitativeconditionssurroundingeachcontractisdifficulttoobtain.Theseareproblemsthatprevailinmostcircumstancesandaredifficulttoovercome.
Tomitigateagainsttheeffectofanincompletesetoffactors,twostrategiescanbeemployed.First,itmaybepossibletorepresentsomeoftheabsentfactorsbysurrogatevariablesthatareinthedataset.Forexample,asmentionedearlier,annualbidvolumehasbeenusedinthepastasaninversemeasureofthelevelofcompetitionprevailingintheconstructionindustryatthattime(Herbsman1986).Similarly,thenumberofplanchangeseachyearcanserveasameasureofdesignquality.Second,ifthemodelingofconstructioncostischangedfromestimatingthecostofindividualprojectstoestimatingoverallconstructioncostseachyear,themodelingtaskissimplified.Thisisbecauseitisnolongernecessarytotrytomodelindividualprojectsinwhichconditionsinflatethepriceinonecaseanddeflateitinanother,sincesuchconditionswouldtendtocancelthemselvesoutamongprojectsinthesameyear.Forexample,firmsthatreducetheirbidpricesinanefforttowinaparticularcontractcouldbebalancedoutwithinthesamefiscalyearbythosethatincreasetheirpricesbecausetheyalreadyhaveenoughworkandarenotparticularlyinterestedinwi
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