U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
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Figure 1 illustrates the Toolkit’s safety analysis process. This process is based largely on the safety analysis process developed in the Highway Safety Manual (HSM). This section describes each step of the process. For more information, including guidance for conducting a given step or links to other resources, please go to the relevant step in the Toolkit.
The first step in conducting safety analysis is compiling the available data. Valuable safety analysis can be conducted with very little data. However, the type of safety analysis that can be conducted and its level of sophistication vary according to the quantity and quality of the data used. The most common types of quantitative data are crash data, traffic volume data, and roadway characteristics. Non-quantitative anecdotal information also is commonly used in safety analysis.
There are typically two situations requiring safety data to be compiled: 1) agency staff or the public are concerned about safety at a particular location; or 2) agency staff seek to better understand safety issues for some portion of the road system, including rural curves and stop-controlled intersections.
A “network” is a collection of roads under the jurisdiction of an agency. In network screening, all or some of an agency’s roadway network is evaluated from a safety perspective. For example, an agency could conduct a network screening of all collector roads and intersections in the community, or all stop-controlled intersections in the community. The purpose is to focus limited resources on the locations most likely to benefit from traffic safety improvements.
While there are many methods for screening road networks, each with unique benefits and drawbacks, only five are presented in the Toolkit. They are:
The outcome of network screening analysis is a list of sites with potential for safety improvements.
Even though it currently is not common practice, network screening is an effective way for an agency to develop lists of candidate sites for safety improvements. This allows the agency to proactively implement a strategic approach to improve safety and, over time, lessen the reactive approach to simply addressing one concern after another.
In cases where the agency is responding to safety concerns at specific location(s), the agency can skip this step and go directly to evaluating conditions at the site (Step 4).
During this step, the list of sites identified in the network screening process is narrowed down to a subset for detailed investigation. In an ideal situation, every one of the sites identified through network screening would be analyzed in more detail. Depending on the number of sites identified, time and resource constraints may limit detailed evaluation of all of them. Therefore, the agency should focus its attention on the most important sites.
Whenever an agency has identified more sites to analyze than it has resources to accomplish, narrowing the list of sites through the use of selection criteria is helpful.
Once the site(s) have been selected for evaluation; crash data, traffic volume data, and roadway characteristics at the selected sites can be studied to identify the factors contributing to the crashes. Stakeholders (e.g., residents, law enforcement officers, maintenance staff) also should be consulted for additional information contributing to safety issues at the sites. This step is referred to as site diagnosis.
The availability of crash data substantially influences the methods available for diagnosis. This step presents information about diagnosing site crash conditions both without and with crash data and identifying countermeasures for a site.
This step is conducted for each site selected for detailed investigation.
If the agency has identified more than one treatment to address crash concerns at a site, the countermeasures are prioritized to identify which have the greatest potential to improve safety. Selecting the most appropriate countermeasure depends on considerations, including feasibility of implementation, expected safety benefits, cost, public opinion, local and state roadway design policies and guidance.
After prioritizing and selecting the most appropriate countermeasure for each site, it may be necessary to select the sites that will actually receive the improvements. This decision is influenced by several factors, including available funding, other construction or maintenance activities underway in the community, funding/grant availability and restrictions, and the estimated safety benefits. Step 5 describes various methods for conducting this prioritization analysis.
This step is needed if more than one optional treatment has been identified for a site and/or the cost of implementing improvements at the study sites is greater than the funds available.
Obtaining the necessary human and financial resources is a major consideration in implementing any safety project or program. While safety funds for project implementation are available from a variety of Federal, Tribal, state, and local programs, harnessing local funding sources and staff resources may be the quickest way to implement projects. For example, maintenance staff can implement low cost projects such as sign replacement, vegetation control, or roadway striping as part of their regular duties.
Agencies also can use locally generated funds as a match to leverage state or Federal dollars. This approach greatly increases the total funding available to implement projects.
While administration of these programs varies throughout the country, this step provides background information about these programs and resources for learning more.
Countermeasures are implemented after they have been selected and prioritized.
The purpose of this step is to describe how to evaluate the impact of the treatments that have been implemented in terms of crash frequency or severity. A reliable assessment of the effectiveness of safety countermeasures cannot be made immediately after implementation. Some time needs to pass, often two to three years, before enough data can be collected to determine how many crashes, serious injuries, and fatalities have occurred since implementation to then compare it with the same types of data from before implementation.
This step should not be overlooked. Evaluation provides information that can help agencies decide whether or not the investment has reduced crash frequency or severity. Evaluation also can help agency staff demonstrate the value of the safety program to community leaders and the general public.
Practitioners should conduct safety effectiveness evaluation two to three years after treatment(s) have been installed.
Each of the two User Guides demonstrates different aspects of the toolkit through the use of hypothetical typical examples.
Using the User’s Guides
User’s Guides are companion documents to the Toolkit and provide realistic examples for users to work through. Although the scenarios may not mirror the issues experienced in your agency, the Guides provide information on how best to use the resources in the Toolkit and example calculations.
The User’s Guides and Toolkit include sidebars with additional tips, technical definitions, and references to other resources. They provide background information and context for users unfamiliar with the technical terms and provide helpful information related to the tools and identify optional or additional analyses that can be conducted.
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