Conducting a safety analysis and applying effective countermeasures are crucial in decreasing the number of collisions, reducing congestion, and maintaining the efficiency of the transportation system.
- Safety data analysis
- Crash data analysis
- Collision analysis
- Safety needs analysis and treatment
- Safety problem identification
In order to maintain the efficiency of the transportation system, it is necessary to identify traffic issues with a safety analysis and address them through effective countermeasures. Data can tell the “safety story” for a given location or community, and this information can help agencies answer questions like:
- Where and when are collisions occurring most often in our area?
- What types of incidents occur more than others?
- Why do these collisions occur?
- What are the common links between them?
To answer these questions, agencies should look at three different types of information:
- Collisions history data answer many of the questions above. Each crash is identified by location, date, and time, and the database provides the number of collisions, severity of any injuries sustained, collision type, contributing circumstances, and the sequence of events.
- Roadway data provides the size and capacity of the road, cross-section design of the roadway and roadside, pavement type, and existing traffic control. It can provide clues about why collisions happen and how an agency might make changes to prevent future incidents.
- Exposure data provides traffic volumes (often measured as average annual daily traffic), the length of the roadway, and the population of people living in the area.
Once an agency defines and prioritizes the safety problems to solve, they should determine which solutions are best to address the identified needs. To calculate the benefits and compare different countermeasures, agencies must consult research and their own experience to determine how effective certain countermeasures are for a variety of collision types. For example, replacing a typical two-way stop controlled intersection with a roundabout can reduce all collision types by 21 percent (1).
Every transportation project has a cost investment including applying countermeasures. With resource limitations at public agencies, not every safety need can be met immediately with a project-level improvement. Cost is an important factor when determining which countermeasures to apply at a given location, and more broadly across the transportation system. Agencies calculate benefits and costs, so they can make “apples to apples” comparisons of different countermeasures.
When funding for a higher-cost safety improvement is not immediately available, sometimes agencies can implement less expensive treatments in the interim. For example, enhanced curve signing or high friction surface treatments can be implemented to address curve crashes while the agency seeks additional funding for a future realignment.
Choosing a countermeasure also means incorporating public acceptance into the decision process. Transportation issues affect everyone, so citizens have opinions about how their system should be designed and operated. Safety is a particularly important subject due to the emotional impact of traffic collisions, especially those involving injuries and fatalities. Bringing the public into the process as soon as possible—even during the initial analysis and review of potential countermeasures—can help create an understanding of the decision-making process, site limitations, budget realities, and any potential undesirable effects of certain treatments.
When to use this strategy
Safety analysis and countermeasure selection are essential for every safety project. Due to the complex nature of the problem being solved, agencies must be rigorous about collecting, analyzing, and interpreting safety data to understand existing conditions. Then, they must be equally resolute about identifying and prioritizing safety treatments.
Safety analysis can be reactive or proactive. Reactive reviews include hot spot analyses when there are a relatively high number of collisions occurring at a single location. Proactive reviews consider entire roadway networks to measure performance.
- Cost-effective use of limited funding to reduce the number and severity of traffic collisions, resulting in fewer people that are impacted by property damage, injuries, and loss of life.
- Reduced congestion from less collisions blocking the road, especially during high-volume times of day.
- A defensible, systematic process based on data helps protect agencies from potential lawsuits if road users are involved in roadway collisions.
What you need in order to implement
- Agencies should focus policies on the collection, analysis, interpretation, and use of safety-related data and countermeasure selection, for safety management and decision-making.
- Understanding of federal and state funding laws, regulations, and policies, including safety-focused funding programs in order to develop and improve safety plans.
- Coordinate with agencies who collect and maintain collision , roadway, and traffic databases. Some will be within a transportation agency, but others will be in other departments. For example, collision data originate from law enforcement incident reports, and in many states these are owned by the state highway patrol.
- Database-manipulation and geographic information system tools to deliver the data to analysts and provide the means for their analysis. Reporting software ranging from basic spreadsheets to graphically-intense tools to produce reports on existing conditions and suggest safety countermeasures.
Agency resources needs:
- Staff qualified to collect, analyze, interpret, and report on safety data.
- Staff qualified to identify and select appropriate safety countermeasures.
Learn more about this strategy
Federal Highway Administration (FHWA), Roadway Safety Information Analysis: A Manual for Local Rural Road Owners, Washington, DC, 2010.
Federal Highway Administration (FHWA), Office of Safety Roadway Safety Data Program website.
Federal Highway Administration (FHWA), Every Day Counts Initiative, Data-Driven Safety Analysis website.
Federal Highway Administration (FHWA), Crash Modification Factors Clearinghouse.
(1) Gross, F., Lyon, C., Persaud, B., Srinivasan, R., "Safety Effectiveness of Converting Signalized Intersections to Roundabouts." Presented at the 91st Annual Meeting of the Transportation Research Board, Paper No. 12-1658, Washington, D.C., (2012).
(2) AASHTOWare Safety Analyst.
(3) Interactive Highway Design Model website.
About key characteristics
Safety analysis and countermeasure selection is necessary for providing safe roadways in all locations.
Most safety analysis is inexpensive, so investing in better analysis and countermeasure identification will make every safety strategy more effective.
Depending on the rigor of the analysis, some analyses require more robust tools and rigorous statistical methods. For example, the Highway Safety Manual’s release in 2010 introduced safety engineers to regression-to-the-mean issues, binomial distribution, and Empirical-Bayes analysis. Tools such as Safety Analyst and the Interactive Highway Safety Design Model provide agencies with the platform for high-level analysis.
Collaboration is necessary with the database owners (collision, roadway, and traffic data) for analysis. These include multiple offices within a transportation agency and other state and local agencies (e.g., state highway patrol, regional planning organizations).
When countermeasures are identified, agencies must collaborate with stakeholders to determine what works best for a given location. Examples include residents and businesses in the geographic area of a new construction project, elected officials who represent those citizens, and the state and federal agencies who will provide funding for potential countermeasures.