IL DOT: Highway Safety Manual

Posted by Content Coordinator on Wednesday, November 21st, 2012




The substantial development effort by the National Cooperative Highway Research Program (NCHRP), the Transportation Research Board (TRB), and the American Association of State and Highway Transportation Officials (AASHTO) has led to publication of the first edition of AASHTO’s Highway Safety Manual (HSM). The HSM is the first comprehensive document providing a scientific, data-supported decision-making tool for practitioners when considering safety explicitly during their daily work. It provides new concepts for application by state highway agencies throughout the safety management process and particularly in the estimation of safety benefits of proposed highway improvement projects. The manual also includes network screening methods to identify potential safety improvement project locations, diagnostic guidance based on historical crash patterns, selection process of appropriate countermeasures, economic analyses, and establishment of project priorities, along with methods for evaluating the effectiveness of completed projects. The HSM also provides predictive methods for estimating the safety benefits of proposed highway improvement projects. Estimating the effect of proposed projects or of several project design alternatives on crash frequencies and severities can now become a routine part of the project development process. It will allow safety to be considered on a quantitative basis in project development the same way as other factors such as traffic operations, air quality, noise, and cost are considered.

The Illinois Department of Transportation (IDOT) in partnership with the Illinois Center for Transportation (ICT) developed analytical tools to identify and manage a systemwide program of site-specific and systematic improvements to develop strategies to prevent and reduce fatalities and severe injuries from motor vehicle crashes. These tools, such as Illinois’ own safety performance functions (SPFs), were developed using advanced statistical techniques for Illinois state highways. IDOT has fully incorporated SPFs into its safety program and has used SPFs to identify locations to be included in the federally required 5% report. IDOT further expects to implement the SafetyAnalyst tool and adopt the AASHTO HSM. Illinois’ participation in the review of the HSM through development has allowed IDOT to begin implementation immediately. Illinois, along with a key group of other states, is aggressively working to implement the HSM. IDOT has worked with those states, FHWA, AASHTO, and NCHRP in a phased approach to implementation, which included hosting a national SPF Summit, providing training to IDOT staff, and the proposed lead state peer exchange.

IDOT sponsored in partnership with FHWA the first-ever Safety Performance Function (SPF) Summit with state DOT representatives across the country. This event created significant benefits to Illinois and IDOT. It allowed IDOT to validate its SPFs and take steps to update them to be in line with the HSM, led to development of a one-day SPF workshop by ICT for IDOT engineers, and ultimately brought IDOT more resources and support from FHWA and AASHTO. Upon the success of the SPF Summit, IDOT was granted the opportunity to host the HSM pilot training in Schaumburg in May 2010, which allowed many Illinois engineers to become familiar with the HSM document and its applications. IDOT has used the training materials from NCHRP Project 17-38, “Highway Safety Manual Implementation and Training Materials,” and expanded this training to all five regions in the state to maximize implementation.

The HSM has the potential to bring about major changes in the accuracy and completeness of safety analyses conducted by highway agencies. However, like any new analysis tool, the HSM will be effective only if it is implemented by highway agencies.

Recent experience has shown that one of the best ways to encourage highway agencies to implement new approaches is to show examples of other agencies that are taking a lead role in the implementation. IDOT and ICT, therefore, sponsored and hosted the HSM Lead State Peer-to-Peer Workshop to facilitate the systematic and effective implementation of the HSM in Illinois and peer states. The purpose of this two-day workshop, held November 17– 18, 2010, at the IDOT District 1 Office in Schaumburg, Illinois, was to disseminate information and facilitate discussions on various ongoing and emerging activities and issues regarding the development and implementation of the HSM. Twenty-four presentations followed by question-and-answer time and facilitated open discussions gave the representatives of 13 lead states and other organizations the opportunity to learn about recent developments by the leading states and federal initiatives. The workshop facilitated the exchange of experiences and examples related to HSM implementation among the lead states by covering a range of topics such as

•    Achievements in the institutionalization of new quantitative safety methods

  • Network screening
  • Policies
  • Construction, design, planning, and operations
  • Leadership and champions

•    Challenges faced and overcoming barriers

  • Data, data needs,methods for completing the dataset
  • Methods for using tools with limited data
  • SPF calibration and SPF development
  • Leadership support and resources
  • Training DOT staff and local agencies


  • Needs and available training
  • Outcome of local training sessions
  • Future plans for training

•    Data, data needs, and tools

  • Sharing data
  • Data collection methods
  • Data integration

•    SPF development and calibration

  • Safety Analyst and Interactive Highway Safety Design Model(IHSDM) 

•    Case studies and applications of the HSM

  • Projects using HSM methods

There was open communication and sharing of experiences, challenges, and successes throughout the workshop, which helped ensure that leading highway agencies benefit from the experiences of other highway agencies. The survey at the end of the workshop showed that all participants found the experience very positive and would like to return to another workshop next year. It was clear that the momentum created at last year’s SPF summit has continued to grow, and we aim to continue these advancements in the explicit quantification of safety. Among the 104 participants, about 50 came from IDOT district and central offices; hence, the workshop also helped IDOT agencies benefit from the experience of leading states in the nation.

Read full report (PDF) here: Highway Safety Manual Lead States Peer-to-Peer Workshop

About The Illinois Center for Transportation (ICT)
“The Illinois Center for Transportation (ICT) is a premier transportation research center that builds on the experience of renowned experts in transportation and related fields at the University of Illinois, the Illinois Department of Transportation (IDOT), and other universities in Illinois and across the country by providing the appropriate tools and support required for objective research.”


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