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外文翻译

（2009届）

题目Ⅰ：

EstimatingFutureHighwayConstructionCosts

2009年2月19日

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