U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Several types of data are needed to develop an effective safety program. This information can assist agencies in identifying locations with safety issues, prioritizing locations, and identifying the most appropriate treatments. It is difficult to solve a problem until information is collected and analyzed to determine the nature of the problem. There are three common types of data needs for a safety project or program:
Crash history data is the primary source of information regarding the traffic safety environment, driver behavior, and vehicle performance. In order to address safety problems, traffic safety data should be timely, accurate, complete, consistent, integrated, and accessible. Good quality data have the potential to improve problem identification, prioritization of project selection, and evaluation of the effectiveness of countermeasures.4
Compared to Federal and State safety professionals, local practitioners tend to be more aware of locations with a history of crashes within their own jurisdictions due to the size of the area and news-worthiness of local traffic crashes. This knowledge, coupled with actual crash data, can aid the practitioner in identifying factors contributing to crashes and allow them to choose improvements to address these issues. The primary sources of crash data for local practitioners include:
The primary and most comprehensive sources of information used to populate crash databases are the crash reports completed by State and local law enforcement organizations. Crash reports are the record of a traffic crash that has occurred on a public roadway. The format of the report varies by State, and sometimes by jurisdiction within a State. See Appendix A for an example of a State crash report.
Crash reports generally include the following information about the incident:
By reviewing the information provided on crash reports over a period of time, recurring variables may be discovered to help pinpoint which factors are contributing to crashes.
The types of information collected and data collection methods used by law enforcement officers vary. Documentation methods among individual officers in the same jurisdiction also vary at times. The local practitioner should be aware of these variances during the review and analysis of crash reports.
There are a number of crash reporting issues that should be considered by law enforcement officers and safety practitioners when working with crash reports. These include:
Location Coding. Exact location of a crash is sometimes difficult to determine because the location of impact is often not where the vehicles come to rest. Referencing crash locations is often dependent on the level of technology used, the experience of the officers at the scene, and the approach used by the jurisdiction.
Typical methods include:
Limited resources often preclude the use of expensive technology, and reference points may be long distances apart, affecting accuracy. In a situation where GPS data is available, Geographic Information Systems (GIS) tools may be available to use these data for in-depth analysis and mapping.
Regardless of the method used, the location of each crash is an important data element for safety analysis.
Crash Type Definitions. Various jurisdictions may define crash report terms differently. For example, whereas rear-end and head-on crash types may be standard classifications in some areas, other regions may interpret these classifications differently or include additional classifications.
Threshold for Reportable Crashes and Severity Determination. States across the country use varying criteria to determine when a crash is deemed reportable and to define crash severity. Reportable crashes are crashes that include a fatality, injury, or property damage cost meeting a specified threshold. Most States have an estimated property damage cost threshold for a property damage only (PDO) crash to be considered reportable. In some States, if the vehicle can be driven away from the scene of the crash and no one is injured, it is not considered a reportable incident.
Jurisdictions are generally consistent with regard to the definition of a fatal crash; but as the severity of a crash diminishes, the classifications can vary by state. The severity of an injury crash is often difficult to determine at the scene and can be subjective based on the reporting officer if follow-up with hospital or Emergency Medical Services (EMS) is not conducted. Local practitioners should be aware of the issues in their States and local jurisdictions during crash data review and subsequent analysis.
Practitioners should also be aware that data issues such as missing, contradictory, and erroneous information have the potential to skew analysis and result in inefficient decision making. Coordination between law enforcement personnel and local road practitioners is important to ensure the efficient collection of crash data.
Statewide crash databases typically offer comprehensive records on all reported crashes. They are compiled from State, county, and municipal law enforcement agencies submitting crash reports to a central State repository. State crash databases typically include the information collected at the scene of the incident.
However, State repositories can vary by agency, depending on the state. Data compilation and dissemination methods can also differ by State and not all States share their collected crash data with local jurisdictions. Moreover, local crash data in the repository can be incomplete. Local practitioners should be aware of the issues in their State and should identify the relevant points of contact necessary to obtain further information.
State data on crash types can provide clues regarding the potential for future severe crashes and countermeasures that could help. For example, if only non-injury roadway departure crashes have been recorded at a particular curve over a period of time, these incidents could be a precursor to a severe crash in the future if this location is not treated, since rural roadway departure crashes tend to be more severe than other types.
The Fatality Analysis Reporting System (FARS) is a national database of fatal crashes that occurred on the national public roadway network. It is maintained and operated by the National Highway Traffic Safety Administration (NHTSA).
FARS contains data derived from a census of all fatal traffic crashes within the 50 States, the District of Columbia, and Puerto Rico. FARS was developed to provide an overall measure of highway safety at the national level, to help identify traffic safety problems, to suggest solutions, and to help provide an objective basis upon which to evaluate the effectiveness of standards and highway safety programs among the States.5
Each State provides specific fatal crash information in a standard format to FARS. The data originate from State accident reports. Once collected by the FARS analysts, the data are recoded to match the standard FARS forms. FARS data are used to answer questions regarding the roadway, vehicle, and driver factors that contribute to traffic safety.6 The benefit to the FARS data is that it includes information on every fatal crash that has occurred within a State; so if a jurisdiction has no other reliable source of data, FARS can provide a starting point.
The FARS dataset is limited to those crashes involving a fatality. In a local rural setting, fatal crashes are relatively rare and random; therefore, FARS data may not provide the best indication of locations with identifiable safety issues.
If on-scene crash data is unavailable, other potential sources of information are local Emergency Medical Services (EMS) and medical centers. EMS data can provide information regarding the locations and degree of EMS responses to traffic crashes. Similarly, hospitals may have some information available regarding emergency room visits or other admissions connected to traffic crashes. Due to a number of Federal and State regulations regarding the privacy of medical information, the availability of these data could be limited and will vary by State.
The Crash Outcome Data Evaluation System (CODES) links crash records to injury outcome records collected at the scene and en route by EMS; by hospital personnel after arrival at the emergency department or admission as an inpatient; or on the death certificate at the time of death. CODES is designed to foster and cultivate crash-outcome data linkages for highway safety applications by State and local practitioners.7
Analyses of linked data can help traffic safety professionals and coalitions to determine and implement data-driven traffic safety priorities. In many States, the State Department of Health (or similar agency) has access to the CODES linkage data, and this information in combination with the State crash database and FARS data, can be beneficial to local safety practitioners supporting safety initiatives.
Potential infrastructure issues, perceived safety concerns, or other traffic-related situations are sometimes reported to the local agency by citizens or citizen groups. The notification is typically delivered by telephone call or e-mail to the officials of a local jurisdiction, and a response is often requested.
The public official should compile records of these notifications so that multiple notifications of the same location can be identified. While this is primarily anecdotal information, public notifications can serve as indicators that a problem may exist and could warrant further review and analysis. Additionally, open communication with local citizens can help practitioners identify potential highway safety issues in the community.
Table 1 shows how a simple database could be designed to capture and store information from the various sources previously discussed.
|Location||Source of Information||Date (MM/ DD/ YYYY)||Type of Information||Problem||Crash?||Nature of Crash||Crash Type||Time of Day (24 hr time)||Weather Conditions||Traffic Conditions||Action?||Date of Action|
|Intersection – Rt 123 and Fox Mill Road||Local Newspaper||3/8/2008||Citizen Complaint||Speeding||N||NA||NA||Pending|
|Route 123 West / 1/2 mile south of intersection with Fox Mill Road to intersection||Local Newspaper||12/1/2007||Citizen Complaint||Drivers losing control at curve||N||NA||NA||Pending|
|Intersection – Route 657 and Glade Drive||Local Police||2/1/2008||Police Report||Crash Report||Y||Vehicle traveling North on Route 657 hit while making left turn onto Glade Drive||Right angle||7:22||Clear||Light volume|
|Route 657; 1/2 mile south of Glade Drive||Local Police||4/1/2008||Police Report||Y||Driver hit tree on shoulder; single vehicle||Roadway departure; hit stationary object||23:03||Snow||Light volume|
|Intersection – Route 657 and Clifton Road||State Police||10/4/2008||Police Report||Crash Report||Y||Vehicle traveling West on Clifton road rear-ended at intersection||Rear-end||19:21||Rain||Light volume|
|Clifton Road; South of Veirs Mill Road||State Police||11/11/2008||Police Report||Y||Driver ran off road on curve; exceeding posted speed||Roadway departure; on curve||12:23||Rain||Light volume|
|Intersection – Route 657 and Glade Drive||Local Police||11/12/2009||Police Report||Crash Report||Y||Vehicle traveling West on Glade collided with vehicle on Route 657||Right angle||10:06||Rain||No traffic|
|Route 657; 1/4 mile South of Glade Drive||Local Police||11/24/2009||Police Report||Y||Driver ran off road; single vehicle||Roadway departure||23:04||Rain||No traffic|
|Intersection – Middlebrook Pike and Waples Mill Road||Maintenance Crew||12/1/2009||Observation||Missing Stop Sign||N||NA||NA||Replaced Stop Sign||12/19/2009|
|Middlebrook Pike; 1 mile North of Running Cedar Road||Maintenance Crew||12/12/2009||Observation||Sign Knocked Down||N||NA||NA||Advanced Curve Warning Sign Replaced||1/8/2010|
It is also valuable to obtain information about the roadway infrastructure. The following roadway data are often used to assist practitioners in safety analyses:
This information can be combined with crash data to help local practitioners identify appropriate locations and treatments to improve safety. For example, if a segment of roadway is experiencing a high number of roadway departure crashes, analysis of the inventory of roadway elements could reveal that the roadway does not have edgeline pavement markings. An appropriate countermeasure could be to install edgeline pavement markings to provide guidance to motorists to stay on the traveled way.
The raw number of crashes can sometimes provide misleading information about the most appropriate locations for treatment. Introducing exposure data helps to create a more effective comparison of locations. Exposure data provide a common metric to the crash data so roadway segments and intersections can be compared more appropriately.
The two most common types of exposure data used are traffic volume and roadway miles.
4 Federal Highway Administration, Crash Data Improvement Program Guide, April 2010. Available at: http://safety.fhwa.dot.gov/cdip/finalrpt04122010/#toc [ Return to note 4 ]
5 U.S. Department of Transportation, National Highway Transportation Safety Administration, "Fatality Analysis Reporting System Fatal Crash Data Overview" brochure, DOT HS 809726, April 2005. [ Return to note 5 ]
6 U.S. Department of Transportation, National Highway Transportation Safety Administration, "Fatality Analysis Reporting System (FARS) Encyclopedia" web site, http://www-fars.nhtsa.dot.gov [ Return to note 6 ]
7 CODES data is collected in a limited number of states. Local practitioners should consult their State highway agency or Local Technical Assistance Program (LTAP) center for additional information.[ Return to note 7 ]