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Page 12 Chapter 5. Data Data series were assembled to cover the vehicle, driver, and environmental factors identified as related to traffic safety. In addition, numerous economic series were collected to attempt to reflect the influence of the economy on traffic safety. This section provides a list and discussion of the data and sources used. The data series collected were at the state level, meaning that the data were collected for each state and year within the period 2001 through 2012. However, data were not available at the state level on vehicle fleets. Accordingly, data on vehicle characteristics at the national level were used in the models. However, unless otherwise identified, all data series are by year and state. The data included all 50 states. The District of Columbia was excluded because it introduced excessive variance and only accounted for 0.1% of traffic fatalities in the period. 5.1 Crash data The National Highway Traffic Safety Administrationâs (NHTSA) Fatality Analysis Reporting System (FARS) is the standard source for data on fatal traffic crashes in the U.S. FARS provides a census file of all motor vehicle crashes in the U.S. that occurred on a trafficway customarily open to the public, and in which one or more persons died of crash injuries within 30 days of the crash. The FARS data set is composed of data compiled by analysts who are housed within each state. Data elements cover crash- level, vehicle-level, and person-level information. The data are collected from police accident reports, death certificates, vehicle registration files, hospital and coroner records, emergency medical service (EMS) reports, state highway department data, and other state records. There is one record for each crash, vehicle, and person involved in a fatal crash (NCSA 2014). FARS data were used for all analysis of fatal traffic crashes in this report. NHTSAâs General Estimates System data were used where it was informative to examine crashes of all severities. GES is a nationally-representative probability sample of police-reported crashes in the U.S. Crashes are sampled by a stratified, hierarchical sampling system, from about 400 police jurisdictions nationally. About 50,000 crash reports are sampled each year. All data in GES were coded from police reports, without any additional investigation. The variables and code levels are largely consistent with variables and code levels in FARS (NHTSA 2014). GES data are sampled through a national sampling structure, and cannot be used to form state-level estimates. 5.2 Sources of other data used Exposure includes all types of measures that reflect the opportunity or exposure to the possibility of a crash. Table 5-1 lists the primary sources of exposure data. Population data are available from the Bureau of the Census, for each state, including counts by state, age cohort, and year. Years between the census years of formal counts are estimated by interpolation. The Bureau of Census also has estimates of state
Page 13 area, which were used to compute population density. Road miles by FHWA function classes were used to normalize state highway expenditures, in order to control for differences in the sizes of states. VMT or vehicle miles traveled is probably the most important measure of exposure used, because it most directly captures exposure to crashes. The FHWA Highway Statistics publication provides annual estimates by roadway function class (including urban and rural) and vehicle type. Highway Statistics also includes vehicle registration data by year and state, as well as many other relevant data series, which will be discussed below (FHWA 1992-2014). Table 5-1 Exposure data series DataÂ SourceÂ PopulationÂ byÂ stateÂ &Â ageÂ BureauÂ ofÂ theÂ Census,Â TableÂ 2.Â IntercensalÂ EstimatesÂ ofÂ theÂ ResidentÂ PopulationÂ byÂ SexÂ andÂ Age.Â SquareÂ milesÂ byÂ stateÂ BureauÂ ofÂ theÂ Census,Â Geography,Â accessedÂ atÂ https://www.census.gov/geo/reference/stateâarea.htmlÂ RoadÂ milesÂ byÂ roadwayÂ functionÂ classÂ andÂ yearÂ HighwayÂ Statistics,Â FederalÂ HighwayÂ AdministrationÂ (FHWA),Â TableÂ hm10Â forÂ eachÂ year,Â 2001â2012.Â VMTÂ byÂ roadwayÂ functionÂ class,Â vehicleÂ type,Â urban/rural,Â nationalÂ HighwayÂ Statistics,Â FHWA,Â TableÂ VMâ1Â forÂ eachÂ year,Â 2001â2012.Â VMTÂ byÂ roadwayÂ functionÂ class,Â urban/rural,Â byÂ stateÂ HighwayÂ Statistics,Â FHWA,Â TableÂ VM202Â forÂ eachÂ year,Â 2001â 2012.Â VehicleÂ registrationsÂ byÂ typeÂ andÂ stateÂ HighwayÂ Statistics,Â FHWA,Â TableÂ MVâ1Â forÂ eachÂ year,Â 2001â2012.Â Data series on employment, the labor force, and unemployment were obtained from the Bureau of Labor Statistics, based on the Current Population Survey (Table 5-2). They are available by year and month for each state; annual state-level estimates were obtained by summing across the employment and labor force counts and taking the average. Employment was defined as the total number of persons on establishment payrolls employed full or part time who received pay for any part of the pay period which includes the 12th day of the month. Unemployed persons were defined as all persons 16 or older who had not employment, were available for work, and had made specific efforts to obtain employment. The labor force was defined as all persons either employed or unemployed according to those definitions. The full definitions can be obtained here: http://www.bls.gov/sae/790faq2.htm#Ques3.
Page 14 Table 5-2 Economic data series DataÂ SourceÂ Employment,Â totalÂ countsÂ ofÂ employedÂ byÂ state,Â month,Â &Â yearÂ BureauÂ ofÂ LaborÂ Statistics,Â CurrentÂ PopulationÂ Survey,Â LocalÂ AreaÂ UnemploymentÂ Statistics.Â LaborÂ force,Â byÂ state,Â monthÂ &Â yearÂ BureauÂ ofÂ LaborÂ Statistics,Â CurrentÂ PopulationÂ SurveyÂ UnemploymentÂ rate,Â byÂ state,Â month,Â &Â yearÂ BureauÂ ofÂ LaborÂ Statistics,Â CurrentÂ PopulationÂ SurveyÂ StateÂ GDPÂ byÂ yearÂ USÂ DepartmentÂ ofÂ Commerce,Â BureauÂ ofÂ EconomicÂ Analysis,Â RegionalÂ EconomicÂ Accounts:Â DownloadÂ StateÂ medianÂ householdÂ incomeÂ byÂ yearÂ USÂ CensusÂ Bureau,Â CurrentÂ PopulationÂ Survey,Â AnnualÂ SocialÂ andÂ EconomicÂ Supplements.Â FuelÂ taxÂ byÂ stateÂ byÂ yearÂ HighwayÂ Statistics,Â FHWA.Â TableÂ MFâ205.Â FuelÂ costsÂ USÂ EnergyÂ Information,Â StateÂ EnergyÂ DataÂ System,Â pricesÂ forÂ regularÂ gasoline,Â dataÂ areÂ convertedÂ fromÂ pricesÂ perÂ millionÂ BTUs.Â Gross domestic product (GDP) estimates by state and year were obtained from the US Department of Commerce. GDP measures the gross productive output of a state, so it is used as a gross estimate of economic activity. The estimates were divided by population estimates to produce GDP per capita estimates. Median household income estimates were obtained from the Bureau of Census Current Population Survey. The estimates available were for two- to three-year periods, not for individual years. Estimates for individual years were obtain by averaging over spans of years. For example, to obtain an estimate for 2010, estimates for 2009-2010 and 2010-2011 were averaged. Household income combines all incomes within a household, while GDP/capita is on a per person basis. All monetary estimates were converted to constant 2013 dollars using the CPI (Consumer Price Index) calculator at the Bureau of Labor Statistics (Bureau of Labor Statistics 2013). Fuel prices were obtained from the US Energy Information Administration, State Energy Data System. Prices for regular-grade gasoline were selected for fuel prices, since they represent the most common grade of fuel used. The prices were converted from prices per million BTUs to gallons, and then converted to constant 2013 dollars. Fuel taxes, in terms of cents per gallon, were available in the FHWAâs Highway Statistics Series, Table MF-205, which tabulates fuel taxes for each state. Again, tax values were converted to constant 2013 dollars and summed with the fuel cost to produce an estimate of the price at the pump. The Insurance Institute for Highway Safety (IIHS) maintains a valuable set of digests of state laws respecting critical aspects of traffic safety. These data were used to develop the indexes on the strength of state belt laws and motorcycle helmet requirements. Belt use rates are available from the continuing National Occupant Protection Use Survey (NOPUS), published annually by NHTSA. The National
Page 15 Institute of Alcohol Abuse and Alcoholism publishes estimates of per capita consumption of beer, wine, and alcoholic spirits. These are available by state and year. Kathleen Klinich of UMTRI has been compiling state laws related to drunk driving and kindly shared data that were used to develop on index of state penalties and regulations. ESC penetration rates were estimated from a Highway Loss Data Institute report. And finally, the penetration of post-1991 model year vehicles into the fleet was estimated using quasi-induced exposure methods. The rate of penetration was used as a surrogate for the spread of more crashworthy vehicles, in response to NHTSAâs New Car Assessment Program and the strengthening of the Federal Motor Vehicle Safety Standards. Table 5-3 Driver- and vehicle-related framework DataÂ SourceÂ SeatÂ belt,Â primaryÂ vsÂ secondary,Â byÂ stateÂ andÂ yearÂ CompiledÂ fromÂ InsuranceÂ InstituteÂ forÂ HighwayÂ Safety,Â digestÂ ofÂ stateÂ laws,Â availableÂ atÂ http://www.iihs.org/iihs/topics/laws/safetybeltuse.Â BeltÂ useÂ ratesÂ CompiledÂ fromÂ NHTSAâsÂ NOPUSÂ program,Â reportedÂ inÂ (ChenÂ andÂ YeÂ 2009;Â ChenÂ 2014)Â BACÂ limit,Â perÂ se,Â otherÂ alcoholÂ relatedÂ lawsÂ andÂ penalties,Â byÂ stateÂ byÂ yearÂ CompiledÂ fromÂ stateÂ laws,Â indexÂ developedÂ fromÂ (KlinichÂ 2016)Â MotorcycleÂ helmetÂ byÂ stateÂ byÂ yearÂ DigestÂ ofÂ motorcycleÂ helmetÂ lawsÂ fromÂ IIHSÂ website,Â accessedÂ atÂ http://www.iihs.org/iihs/topics/laws/helmetuse/helmethistory?Â topicName=Motorcycles#tableDataÂ AlcoholÂ consumptionÂ CompiledÂ fromÂ NationalÂ InstituteÂ ofÂ AlcoholÂ AbuseÂ andÂ Alcoholism,Â (Haughwout,Â LaValleeÂ etÂ al.Â 2015)Â ESCâpenetrationÂ CompiledÂ fromÂ HighwayÂ LossÂ DataÂ InstituteÂ reportÂ onÂ theÂ penetrationÂ ofÂ collisionÂ avoidanceÂ technologies,Â (HighwayÂ LossÂ DataÂ InstituteÂ 2014)Â Post1991Â modelÂ yearÂ EstimatedÂ fromÂ GES,Â usingÂ aÂ quasiâinducedÂ exposureÂ technique.Â Â Data series on state highway expenditures are available in the FHWAâs Highway Statistics series. This series is an exceedingly valuable resource for highway safety. Each year, states report highway spending disaggregated by several types of activities, using a set of common forms, definitions, and instructions. Funding under the Highway Safety Improvement Program (HSIP) was compiled from FHWA funding tables under SAFETEA-LU (2005) and MAP-21 (2012), which are available on the FHWA website (see Table 5-4).
Page 16 Table 5-4 Highway expenditures DataÂ SourceÂ CapitalÂ expendituresÂ CompiledÂ fromÂ HighwayÂ Statistics,Â FHWA,Â TableÂ SFâ2,Â includesÂ construction,Â relocation,Â resurfacing,Â restoration,Â rehabilitationÂ andÂ reconstruction,Â widening,Â capacityÂ improvements,Â restorationÂ ofÂ failedÂ components,Â additionsÂ andÂ bettermentsÂ ofÂ roadsÂ andÂ bridges.Â SeeÂ (FederalÂ HighwayÂ AdministrationÂ N.D.)Â MaintenanceÂ CompiledÂ fromÂ HighwayÂ Statistics,Â FHWA,Â TableÂ SFâ2,Â includesÂ preservingÂ theÂ entireÂ highway,Â includingÂ surface,Â shoulders,Â roadsides,Â structures,Â andÂ trafficÂ controlÂ devices,Â asÂ closeÂ asÂ possibleÂ toÂ theÂ originalÂ conditionÂ asÂ designedÂ andÂ constructed.Â Administration,Â research,Â planningÂ CompiledÂ fromÂ HighwayÂ Statistics,Â FHWA,Â TableÂ SFâ2,Â includingÂ allÂ generalÂ andÂ miscellaneousÂ expendituresÂ notÂ relatedÂ toÂ aÂ specificÂ project,Â expendituresÂ forÂ highwayÂ planning,Â research,Â andÂ planningÂ LawÂ enforcementÂ andÂ safetyÂ CompiledÂ fromÂ HighwayÂ Statistics,Â FHWA,Â TableÂ SFâ2,Â includingÂ allÂ relevantÂ FederalÂ SafetyÂ programs,Â sectionsÂ 402,Â 403,Â 405,406,Â 407,Â 408,Â 410,Â andÂ 411Â ofÂ TitleÂ 23Â ofÂ theÂ UnitedÂ StateÂ Code,Â asÂ wellÂ asÂ MCSAP.Â AlsoÂ includesÂ capitalÂ expendituresÂ designatedÂ byÂ statesÂ asÂ safetyâ related.Â HighwayÂ SafetyÂ ImprovementÂ ProgramÂ CompiledÂ fromÂ FHWAÂ fundingÂ tablesÂ underÂ SAFETEAâLUÂ andÂ MAPâ21,Â availableÂ fromÂ https://www.fhwa.dot.gov/safetealu/fundtables.htmÂ andÂ https://www.fhwa.dot.gov/map21/funding.cfmÂ Highway spending was used in the statistical models to capture the effect of infrastructure and state highway programs on safety. Clearly, highway spending is an imperfect surrogate because the cost- benefit ratio of projects differ. However, it is believed that this surrogate is the best currently available. There are evaluations of specific projects, and crash modification factors (CMF) have been developed for different types of projects, e.g., (AASHTO ; AASHTO 2010). But there are no comprehensive data to translate CMFs into variables that capture the effect of modifications in a system-wide fashion. For example, there is an ample literature evaluating the safety effect of installing rumble strips on shoulders and centerlines, but no comprehensive data on the penetration of rumble strips into the roadway system. Moreover, a safety-related spending variable was constructed that aggregates all spending states themselves identified as safety-related: law enforcement, state educational safety programs, and the portion of capital spending that the states declared to be safety-related. Finally, it is assumed that state departments of transportation attempted to deploy their resources effectively. There are no doubt variations in effectiveness, but in light of currently available data, highway spending should be a reasonable approximation.