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HSM Implementation Guide for Managers - Section 3

HSM Implementation Guide for Managers

3. HSM Implementation Opportunities in Program Development and Project Delivery

The core mission of state DOTs and other similar agencies is to develop and manage a transportation system. Managers explaining and promoting the HSM will find that explaining its potential use in the context of the project development process in their state will resonate with staff. The emphasis here should be on all projects and all activities, not just those that refer to “safety.” Most projects that comprise a state’s program are not “safety projects” but rather are prioritized for other reasons. Regardless of the project’s purpose and need, the HSM offers benefits and can be used in the delivery of the overall program and each project.

FHWA also maintains a Crash Modification Clearinghouse. HSM content on crash modification factors (CMF) is in Part D. As research continues and the knowledge base grows, agencies will want to take advantage of HSM-quality CMF research. The FHWA Clearinghouse is a core tool that most states are using.

Exhibit 4 shows a typical project development process and opportunities to implement the HSM. The following is an overview of how implementing the HSM can influence program and project delivery. As training progresses and policies are changed, eventually actual project applications will gradually become the norm for the agency’s delivery process. Strategies and insights for successful project delivery implementation are included in each section.

Program Development

The Federal Aid Highway Program includes a portion of every state’s allocation specifically set aside for safety improvements. Within each state program, these funds are subject to a formal prioritization process that takes into account crash history and exposure. The HSM can enhance the effectiveness of that prioritization process, as well as providing data to support the allocation of additional state and Federal funding to address safety needs.

The HSM offers improvements over many agencies’ historic approaches to the Highway Safety Improvement Program (HSIP). For example, HSM methods and concepts from Part B were incorporated within the Illinois DOT’s process for developing their “Five Percent Report” to the FHWA. Over time, the HSM-based methods were refined and found so valuable that the report replaced Illinois DOT’s old methodology for identifying safety projects. Illinois DOT District staff was at first encouraged to use the data and methods in Parts B and D, and eventually required to use them to have their HSIP projects funded. DOT developed a benefit/cost tool with CMFs to staff. The tool, using HSM values for CMFs, supports consistency in approach and a high degree of confidence.

EXHIBIT 4. The Project Development Process and Opportunities to Implement the HSM

Exhibit 4: Graphic: A circle represents the five phases of a typical project development process and opportunities to implement the Highway Safety Manual.

A lesson learned from this exercise involves the use of consistent approaches to CMF applications at the state program level. The published HSM is dated to 2007. FHWA’s CMF Clearinghouse is kept current with published CMF research. The Clearinghouse may contain multiple CMF studies with differing values for the same treatment or countermeasure. State managers need to recognize and address the issue of who decides which CMF is appropriate, what constitutes a minimum level of technical acceptability to the agency and how to keep the agency’s list of approved CMFs current as more are added to the Clearinghouse.

Another decision and action to take includes how crashes and their outcomes will be valued. The HSM offers the “willingness to pay” approach to valuing crashes and severity, but there are other methods used (including a different valuation used in AASHTO’s RSAP program for roadside design). Again, a common and consistent approach should be determined and then communicated as part of program development guidance and documentation.

Project Development

The HSM also offers opportunities to influence how agencies develop individual projects. Early in project development, key decisions are made that influence how the project will be completed. These include defining project scoping, project purpose and need, project objectives, and from all of these, which “track” the project will follow. In later stages, as the project takes shape, detailed studies establish the basic footprint and attributes of the project.

Actual implementation of the HSM within projects should be planned in cooperation with Districts and project managers. As an example, Florida DOT instituted a pilot program with its Districts, in which specific projects typical of the District’s work were identified and HSM methods tested. District involvement in the identification of projects and assistance of the HSM team in data gathering, coding, and interpretation of the results produced understanding and buy-in to the process and tools. Implementing agencies may consider working with one or two Districts with strong champions and interest, establish the process, and then extend it to other Districts.

Project Scoping and Design Criteria

At project initiation, agencies conduct a project scoping exercise. This includes all offices concerned with any aspect of the project, as well as external partners such as the FHWA. Project objectives, project limits, and coordination activities are discussed and established.

Project scoping decisions and establishment of design criteria can have a significant influence on the cost, physical feasibility, and ultimate value of a project. Direct incorporation of HSM-based analyses as part of agency scoping offers significant cost-saving potential without degrading overall safety performance.

Many projects involve an existing facility. For such projects that are not envisioned to include major lane or capacity additions, the safety performance of the existing facility can play an important role in defining the scope of the project.

Scoping Using the Two Dimensions of Safety

Existing highways, intersections, and streets will have crash records, traffic volume data and known geometric features. Agencies that have implemented the HSM will have predictive methods that can provide insights on how the existing safety performance (substantive safety) is relative to a threshold representative of other sites with similar characteristics. The threshold, established by the agency with reference to the HSM methods, quantifies the anticipated average performance of a typical site to identify potential for improvement. The comparison answers a basic question – Is this site/project performing as or better than expected in terms of the number and severity of crashes (Yes or No)?

The second dimension of safety, its nominal safety, is straightforward to understand. Given the design characteristics of the facility, does it meet current design criteria and standards of the agency or not? (Or perhaps more precisely, to what extent and for what geometric features is the location either “nominally acceptable” or not?). Armed with these simple answers an agency could as a matter of project development policy implement a performance-based design decision approach across the two dimensions of safety.

There are many reconstruction projects in which one or more geometric features do not meet current criteria and standards. This case is very typical of roads designed and constructed more than 30 years ago when design standards were much different. If the existing safety performance record meets or exceeds (is better than) the agency’s threshold of acceptability, the agency may reasonably and confidently scope the project as a 3R project, retaining the basic geometry and thus avoiding incurring of potentially substantial construction costs as well as avoiding or mitigating environmental conflicts and additional right-of-way acquisition. The key insight is that applying HSM knowledge can prevent costly investments made in the name of safety when no actual benefit or return from such investments should be expected.

Purpose and Need

The identification of the fundamental reason for the project – its “purpose and need” is among the most important project drivers. This should be a performance-based determination, whether the problem is pavement or bridge condition, delay, travel time or level of service, or safety. Clearly, the HSM offers the best means of establishing a science-based and hence defensible approach to defining whether the performance of the facility merits “safety” being mentioned as part of its purpose and need.

Project Planning, Alignment, and Alternative Studies

HSM methods and concepts have clear application to development of project alternatives. Indeed, the forerunner of the HSM, FHWA’s Interactive Highway Safety Design Model, which executes through software the predictive methods in Part C of the HSM, is an interactive tool to be used during the design process to iterate and understand implications of design decisions in the same way that cost analysis and estimation tools are used to understand differences in quantities and construction costs. Applications apply not only to projects involving the same highway type, but also studies in which a different type is envisioned. The best example of these is conversion of an existing two-lane highway to a multilane facility. Such projects often involve multiple alignments and can include different cross sections.

One insight gained through training sessions of state DOT staff is that the manner in which Part C can be used may vary. In fact, many designers may never actually use the HSM to calculate the anticipated long-term safety performance of a site such as the one being designed (predicted average crash frequency) or the long-term performance of an existing site (expected average crash frequency). But merely using the HSM Part C as a reference, designers can easily gain insights on the relative safety performance of design alternatives they typically consider, and adjust their thinking about how to make good design decisions.

The training of designers has focused, for the most part, on the importance of nominal safety. Many designers have been taught that adherence to nominal safety directly translates into substantive safety performance. The following list presents general understanding by designers unfamiliar with the highway substantive safety knowledge base in the HSM:

Managers can encourage designers to learn and apply the HSM knowledge base even if they will not actually apply the predictive methods. In doing so, the quality of their work will be greatly enhanced. The ability of a designer to consider substantive safety is strongly dependent on a sound understanding of HSM concepts and the science of safety captured in Part C of the HSM (predictive method) and positive guidance principles described in Chapter 2 of the HSM. The National Highway Institute has a number of courses that has more of a road design focus:

Also, AASHTO produced a three-hour webinar on Flexibility in Design that provides background on the relationship of design criteria to performance and offers insights on design decision-making in reconstruction.

Application of the HSM in day-to-day activities should follow training as soon as possible. Direction and technical assistance may be necessary during these initial efforts to use the HSM.

The extent to which the HSM can be immediately used following training to inform the design process depends on several factors. With state-specific calibration factors or state-specific SPFs already available, designers can quantify actual long-term expected safety performance of a facility, considering both the number and severity of crashes.

Several states are currently in the process of calibrating HSM Safety Performance Functions (SPF) and the development of state or region-specific SPFs. During this development period, designers can still use the HSM Part C to assess relative differences among alternatives within the same facility type and control type. However, the output from an HSM SPF cannot be used or described as an actual prediction, as it lacks the necessary calibration factor. Calibration of the HSM SPFs is necessary for full predictive capability because the SPFs in the HSM are based on the data from a subset of states. Differences in crash data quality, roadway inventory data, traffic volume counts and estimations, minimum crash reporting thresholds, topography and weather conditions are but some of the factors that vary among states that may impact the number and severity of crashes.

Managers will need to weigh the advantages and disadvantages of promoting the immediate use of the HSM and the timing of delivery of training for staff in states with SPF or calibration development efforts that may take some time. Rather than hold off on training or any use of the HSM, the identification of implementation opportunities before the training would be useful. The training can then include some discussion of the particular approach that the agency will take in terms of implementation of the HSM in the project development process.

Design and Context Sensitive Solutions

In many projects, conflicts can occur between what a designer may perceive as the best design (i.e., one that is nominally safe) and what may be achievable due to environmental constraints or conditions, public acceptability and availability of right-of-way. Context Sensitive Solutions as outlined by AASHTO and NCHRP Report 480 addresses these four critical success factors:

Virtually all aspects of project development have evolved to state in which DOTs can provide quantitative, high-quality data on the performance of an alternative, with the exception until now of safety performance. Indeed, the extent of safety analysis frequently applied to contentious or difficult projects is the nominal safety model. With HSM methods and approaches, agencies can better fill in the missing piece and not only make better decisions but have the basis for explaining and defending their decisions.

The final step in the initial planning part of the project development process is identification of a preferred design alternative. This is typically done when design is about 30 percent complete, i.e., when the alignment and cross section are established. The HSM can then be used to perform predictions of safety performance compared to other alternatives, or to a “no-build” option.

Preliminary and Final Engineering

As the selected concept is detailed, changes may occur. Other major design decisions such as maintenance of traffic plans are developed. During preliminary engineering the design documentation is prepared and approvals sought. It is during this stage that design exceptions may be fully outlined, studied, and approved.

Design exceptions – the use of a design value outside the established criteria for the project, are a common and indeed routine part of project development. A design exception represents an acceptance that the design will not be “nominally safe.” Some designers and some agencies resist design exceptions either because of tort liability fears or their genuine belief that safety performance (substantive safety) will be compromised.

The HSM offers concepts and methods for design engineers to understand the implications of their actions and thus improve decision-making. Insights evident in applying the predictive methods and CMFs, include the following:

Designers attuned to the nominal safety model but not to the contents of the HSM may have a mindset that any change of a standard design parameter would result in a significant change in the safety performance of the facility. For example, a reduction in lane width from 12 feet to 11 feet may thought to be reducing safety performance substantially in an abrupt and immediate manner, i.e., the change makes the facility unsafe and 12 feet made the facility safe. Actual or substantive safety performance is, however, does not represent such an absolute change in safety but rather a gradual change in safety. It is important to keep in mind that such a relationship with substantive safety may not even exist. Designers who have learned about substantive safety, and marginal or incremental changes in safety performance suggested by CMFs and predictive models, will understand the change in safety is likely gradual and be able to act accordingly. Several states that started with the implementation of the HSM reported that the HSM adds value to the evaluation of design exceptions and the documentation process.

Besides allowing designers to quantify the impact of design exceptions, the HSM also offers the opportunity to quantify potential safety performance benefits of mitigation strategies at locations where design exceptions are considered. The FHWA Mitigation Strategies for Design Exceptions (FHWA 2007) offers a resource to design managers.

Operations and Maintenance

The HSM includes information to inform those charged with operating and maintaining the system. Full knowledge and application of the HSM contents in this area may lead agencies to rethink or revise their operating strategies. Examples may include incorporating quantitative safety consideration when timing of signals (provision for protected only left-turn phasing), considering access management strategies, decides when to allow or prohibit of on-street parking, and even maintenance in adverse weather conditions: snow removal strategies.

Managers studying the HSM may find that the 1st edition of the HSM is limited in offering quantitative safety information for all operations and maintenance activities. As with the first edition of the Highway Capacity Manual (HCM), the expectation is that over time, the HSM will be updated to reflect the growing body of research on the impact of maintenance and operational effects on crash frequency and crash severity.

Page last modified on October 15, 2014
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