A new generation of safety analysis tools and methods have been developed to help identify safety issues and provide recommendations for improvements, including the HSM, SafetyAnalyst, IHSDM, and the NCHRP Series 500 Volume 19: A Guide for Collecting and Analyzing Safety Highway Safety Data. These safety analysis tools require quality roadway, traffic, and crash data to achieve the most accurate results. The FDE/HSIP will help support the use of these tools. This section includes an overview of the data requirements for these tools and how these tools can help DOTs to support their HSIPs and SHSPs. Table 4 presents an overview of the tools and for which data analysis procedures they can be used.
Table 4 . Data Analysis Tools by Analysis Procedures.
|
Data Analysis Tools |
Network Screening / Prioritization |
Countermeasure Selection |
Evaluation |
|---|---|---|---|
|
SafetyAnalyst |
|
|
|
|
Highway Safety Manual |
|
|
|
|
Interactive Highway Safety Design Model |
-- |
|
|
|
NCHRP Series 500 Data and Analysis Guide |
|
|
|
It is important to note that this is not an exhaustive list of available tools. The elements included in the FDE/HSIP were selected in part based on the basic data requirements to use these tools. However, the FDE/HSIP are not exclusive to these tools. The FDE/HSIP are the basic elements that any State should be collecting and using in their safety programs to conduct sophisticated safety analysis. FHWA recognizes that many States are developing sophisticated analysis tools in-house that will help to support their HSIPs. All States should be moving towards using sophisticated analysis tools and having the FDE/HSIP to utilize these tools, regardless of whether they are the tools described in this section or they are developed in-house.
Highway Safety Manual
The HSM provides techniques and methodologies to quantify the safety-related effects of transportation decisions, similar to how the Highway Capacity Manual (HCM) quantifies operational impacts (10). The HSM facilitates roadway planning, design, operations, and maintenance decisions based on consideration of their safety impacts. The primary purpose of the HSM is the introduction and development of analytical tools for predicting the impact of transportation project and program decisions on road safety. Benefits to using the HSM include improved decision making and more effective countermeasure selection to reduce the number and severity of crashes, as well as cost savings. The target audience of the HSM is any transportation professional, including State and local transportation agency personnel, engineering consultants, etc.
The HSM is divided into four parts:
- Part A: Introduction, Human Factors, and Fundamentals.
- Part B: Roadway Safety Management Process.
- Part C: Predictive Method.
- Part D: Crash Modification Factors.
There are three primary categories of data that are required for the HSM: crash data, roadway characteristics data, and traffic data. More information on the HSM can be found at http://www.highwaysafetymanual.org/Pages/default.aspx.
SafetyAnalyst and the IHSDM are software implementations of the HSM and are discussed in further detail in the subsequent sections.
SafetyAnalyst
SafetyAnalyst is a software implementation of Part B of the HSM (11). It is a stand-alone set of software tools used to identify and manage a system-wide program of site-specific highway safety issues and recommended improvements. It uses state-of-the-art safety management approaches and incorporates a cost-effective analysis to help guide the decision-making process to identify specific safety improvements that involve physical modifications of the highway system. SafetyAnalyst is beneficial in helping highway agencies to get the most safety benefit from each dollar spent on a project. The software includes six different tools: Network Screening, Diagnosis, Countermeasure Selection, Economic Appraisal, Priority Ranking, and Countermeasure Evaluation.
The minimum set of data elements required to use SafetyAnalystincludes the following: roadway segment characteristics, intersection characteristics, ramp characteristics, exposure data, and crash data. More information on SafetyAnalyst can be found at http://www.safetyanalyst.org/.
Interactive Highway Safety Design Model
The IHSDM is a stand-alone collection of software analysis tools used to evaluate the safety and operational effects of geometric designs on highways and implements Part C of the HSM (12). The IHSDM is a decision-support tool that gives explicit, quantitative evaluations on existing and proposed geometric designs. The intended users of the tool include highway project managers, designers, and traffic and safety reviewers in State and local highway agencies, and consulting firms. There are six evaluation modules: Policy Review, Crash Prediction, Design Consistency, Intersection Review, Traffic Analysis, and Driver/Vehicle. The Crash Prediction Module estimates the frequency and severity of crashes that can be expected on a roadway based on geometric and traffic conditions. This model can evaluate rural two-lane highways, rural multilane highways, and urban and suburban arterials. The benefits of the IHSDM are that the results not only help users to make decisions to improve the safety performance of their roadways, but the results also justify and defend geometric design decisions.
Data requirements to use the IHSDM include roadway, traffic, and crash data. Specific data requirements will depend on which safety module is used. More information can be found at https://www.fhwa.dot.gov/research/tfhrc/projects/safety/comprehensive/ihsdm/.
AASHTO's NCHRP Series 500 Data and Analysis Guide
Volume 19: A Guide for Collecting and Analyzing Safety Highway Safety Data, part of the NCHRP Report 500 Series, is a guide to assist State and local agency users in locating and analyzing safety data as part of their safety efforts (13). The purpose of the Guide is to provide a basic three-stage procedure for use in developing an emphasis area plan, as well as define data-related procedures that will guide the user in selecting potential treatments and target strategies.
At a minimum, crash data are required to develop a safety plan. The guide discusses other data that are useful in addition to crash data, providing descriptions of the major data types, and where the data might be found if not readily available in the user’s jurisdiction. More information on this guide and the other guides in the NCHRP 500 Series can be found at https://www.trb.org/Main/Blurbs/152868.aspx.