北交大-交通安全2

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1、Chapter2TrafficAccidentStudiesandAnalysisA.CrashDataSelectionInformationoncrashesrelatedtothestudybeingconductedshouldbeseparatedfromthelargedatabaseorformhardcopies.Oneofthefirstconsiderationsinseparatingrelatedcrashesforconductingaccidentstudiesistodecideatimef

2、rame.Datafromoutsidetheselectedtimeperiodwillnotbeconsidered.Therearetwofactorstobecompromised:(1)Desireforlargersamplesized,and(2)Desirefortimeframeswithinwhichconditionshavenotchangedtoomuch.Oncethestudytimeframeisdecided,crashdatashouldbeseparatedoutcorrespond

3、ingtothattimeperiod.Therearetwotypesofstudylocations:spotsandsections.Spotsareshortsegmentsoftheroadwaythathelpidentifytheproblempointlocation,suchasintersections,curves,andshortbridges.Geometricandotherfeaturesataspotshouldbenoticeablydifferentfromsurroundingspo

4、ts.Recommendedspotlengthsarefrom0.2to0.3miles.Sectionsarelonger,ratherhomogeneoussectionsoftheroadway.Recommendedsectionlengthsarefrom1to2miles.Precisedefinitionsforthelimitsarerequiredforanalyzingintersectioncrashes.Afixeddistanceof100-200feetalongeachoftheappro

5、achleadingtotheintersectionisusedinmostofthecases.Reducingcrashdatabasedonothervariablesmayberequiredbasedonthepurposedofthestudy.Interestmaybeonthecrashtype,timeoftheday,monthsoftheyear,weather,typesofvehicles,driverconditions,ageofthedrivers,etc.B.CrashRatesand

6、TheirUseBasisforUsingCrashRatesAbsolutenumberofcrashesmaynotgivethetruerepresentationofthesafetysituation.Manystatisticsarepresentedintheformofrates.Twobasedcategoriesincrashrates:(1)populationbasedand(2)exposurebasedCommonbasesforpopulationbasedrates:Areapopulat

7、ionNumberofdriverlicensedpopulationNumberofmotorvehicleregisteredHighway(roadway)mileageCommonbasesforexposurebasedrates:Vehiclesmilesoftravel(VMT)Vehicleshoursoftravel(VHT)2.BasicCrashRatesa.CrashratepermileR=crashratepermileA=totalnumberofcrashesontheconsidered

8、section(usuallyfor1year)L=lengthofthesectionb.Crashinvolvementrate:R=crashratepr100millionvehiclemilestraveledN=totalnumberofdriversofvehiclesinvolvedincrashes