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FHWA Highway Safety Programs

II. Applying the HSM in Planning

Planning is the first stage of the project development process. It is the stage in which broader community visions and goals are related to the transportation system and multimodal transportation network is evaluated to identify priorities, projects, programs, and/or policies to address long-term (i.e., 20 years) system needs. The broad range of potential needs can relate to such issues as enhancement of mobility and accessibility, policy recommendations, pedestrian and bicycle connectivity programs and projects, signal system coordination, transit improvements, freight systems, coordination of land use, intelligent transportation system improvements, safety needs, or parking system management.

Systems planning ranges from the initial definition of a community vision to the actual monitoring of the performance of the projects that have been implemented. The primary purpose of systems planning is to provide the information necessary and needed by decision-makers to make choices about investment in the transportation system consistent with a community’s vision. (NCHRP 541: Consideration of Environmental Factors in Transportation Systems Planning, page 9.) System planning often starts with policy-level documents leading to modal plans and programs. The modal plans and programs can be mode-specific (e.g., freight, transit, nonmotorized, and highway) and documented in one comprehensive plan or by separate plans that focus on select topic areas. The planning process should consider the interaction among different modes in developing a multimodal system plan. The mode-specific and multimodal plans culminate in a prioritized list of projects for the 20-year horizon of the plan. In some cases, the long-range plans will also identify the need for additional refined analysis in a specific corridor or subarea within the community.

Quantitative performance measures in safety commonly include crash frequency, fatal and serious injury crashes, or percent changes in crash frequency or severity. Safety performance (e.g., crash frequency or crash severity) of alternative transportation networks under consideration can be estimated and compared to each other to evaluate safety conditions under different scenarios. The differences in safety performance between the various transportation networks should then be considered as one of the decision factors along with the differences in traffic operations (e.g., level of service), environmental impacts (e.g., air quality), or neighborhood livability (e.g., pedestrian access to transit).

This section discusses how agencies can use tools in the HSM to evaluate safety performance and support the integration of safety explicitly in long-range transportation plans and more specifically in corridor studies. State departments of transportation have safety analysis business units that may be able to provide support to local agencies in acquiring the data and/or conducting safety analysis.

1. Integrating Highway Safety Manual Analysis Methods into a Long-Range Transportation Plan

Federal legislation has increasingly emphasized the importance of safety in transportation planning. The intent is not just to identify safety-specific projects, but to explicitly consider the impact of planning decisions on crash frequency and severity. For example, if an agency is considering an access management policy on all arterial roadways throughout the community, the change in crash frequency or severity can be a consideration in the decision-making process in addition to potential traffic operations and/or economic impacts. Part D of the HSM provides crash modification factors (CMF) quantifying the effects of changing driveway density on urban and suburban arterials. Or if a community is considering a “roundabout first” policy, CMFs related to roundabouts and the effects of changing intersection traffic control to a roundabout are provided in the manual.

If a community is undertaking a long-range planning process to identify 20-year transportation system needs, one of the early activities is to evaluate existing transportation conditions related to mobility and accessibility, pedestrian and bicycle connectivity, and transit service. Part B of the HSM provides network screening methods to identify sites with potential for safety improvement. These sites can be evaluated to identify specific improvements and subsequently prioritized alongside other sites with particular capacity, operational, or connectivity needs. The agency can then use the results from this process to develop a prioritized list of sites for project programming and forward some of these projects into the regional planning process.

PlanSafe software, developed through NCHRP research estimates the future safety performance of different transportation networks at the transportation analysis zone (TAZ) level. While not part of the HSM, this software can be used as part of the future network evaluation stage of a long-range transportation planning project.

2. Integrating the Highway Safety Manual into Corridor Planning

As an outcome of the long-range planning process, an agency may undertake a refined corridor-specific plan. In this type of project, the effort may be focused on evaluating alternative cross-sections, functional classifications, access management concepts, use of a context-sensitive solutions approach for a specific corridor. For example, it may be that a community’s long-range plan identified the need for additional roadway capacity in a corridor without specific details on the proposed facility. The corridor-specific plan would examine additional considerations related to the corridor cross-section and interaction with adjoining land uses and stakeholders needs. Options for medians (including type and location), number of lanes, and/or provision of on-street parking are among the issues that may be considered in this process.

The HSM predictive method can be used to estimate the changes in crash frequency of many of these geometric features for different facility types. Alternatively, an agency can estimate the influence of the type and frequency of intersections, driveways, parking, or median types on the crash frequency for an urban or suburban arterial. Such information may be useful in assessing the effects of different land use plans for a subarea, each requiring a different road network characteristic.

Further, a variety crash modification factors (CMFs) from Part D of the Highway Safety Manual could be applied to the corridor to estimate the change in crash frequency on the corridor under possible alternative development concepts.

3. Tools to Support Application of the HSM in Planning

Tools to Support HSM Application in the Long-Range System Planning Process

AASHTOWare SafetyAnalyst is a tool that can be used to perform planning-level screening. SafetyAnalyst allows the user to select from a variety of safety performance measures and screening methods (listed in Chapter 4, Part B of the HSM) to identify sites or corridors with potential for safety improvement. The agency can use this tool to screen the transportation network or part of the network, where the minimum required data are available for the analysis. For more information, visit the SafetyAnalyst web site. Other agency-specific or commercial software may be available or under development to incorporate some or all of the performance measures and screening methods in the HSM.

FHWA developed a case study showing how Ohio DOT is using AASHTOWare SafetyAnalyst to assist with all steps of their safety management system, including network screening, diagnosis, countermeasure selection, economic appraisal, prioritization, and countermeasure evaluation. More case studies can be found on the HSM web site (FHWA 2012).

The FHWA Safety Performance Measure Primer is also available as a resource to help identify additional performance measures.

PlanSafe is a software tool that was developed through NCHRP. While macro-level safety prediction approaches (such as PlanSafe) are not included in the first edition of the HSM, agencies can use PlanSafe to compare differences in crash frequency or severity across different future development and network scenarios. More information about this tool is available at the TRB web site. An updated version of the software is anticipated in the summer of 2012.

Tools to Support HSM Application in Corridor Planning

Spreadsheets are available to perform basic HSM predictive analysis. This includes the spreadsheets developed as part of the NCHRP 17 38 HSM Training Materials project for training purposes. The Alabama Department of Transportation (ALDOT) and Virginia Department of Transportation (VDOT) released a set of spreadsheets that extends the functionality and ease of use of the NCHRP 17 38 spreadsheets. These spreadsheet tools are available from the TRB Highway Safety Performance Committee web site. Other states, such as Illinois and Washington developed state-specific spreadsheet tools that can be used for corridor planning.

The FHWA CMF Clearinghouse is an on-line, free database of treatments and crash modification factors. The user can query specific treatments (also known as countermeasures) in the on-line database of over 4,000 CMFs. It includes all CMFs published in the HSM as well as those published since the HSM was released. The FHWA updates the Clearinghouse regularly.

Most state departments of transportation have some type of safety analysis and/or crash data analysis unit. This group will manage statewide safety programs such as the state Strategic Highway Safety Plan. The group may also manage safe routes to schools, safety belts, commercial vehicle, or impaired driving programs. Most states will also have traffic records/data analysis units that work with state crash data records. The staff in data analysis units and the safety analysis units can be called upon to support local efforts to integrate safety into planning.

4. Example Application: Long-Range Transportation Plan

The following scenario presents an example of how a MPO would apply the HSM in a long-range transportation plan. The example application introduces a hypothetical scenario to demonstrate an application of the HSM as part of a set of example discussions in subsequent sections. The examples in this guide are not provided to demonstrate how to perform the analysis but rather demonstrate how applying the HSM may be integrated into existing planning, design, and evaluation processes.

An MPO is developing their regional transportation plan. The local agency is conducting the needs assessment phase of the project. In addition to the pedestrian, bicycle, and congestion assessment, the MPO has conducted a network screening analysis on the major roadway systems (freeways and arterials) to identify particular corridors with potential for safety improvement. The MPO selected two performance measures from the HSM: equivalent property-damage only (EPDO), and excess expected crash frequency. Using the peak searching method, the analysis identified roadway segments where reported crashes exceeded the expected number of crashes based on the characteristics of the roadway and the safety performance function associated with that roadway type. This method took into account the variation in crash data from year to year. The agency identified several corridors that may benefit from investment and prioritized the corridors. Exhibit 3 summarizes the results. They identified the corridor on Route A, from milepost 5.6 to 8.1, as the corridor with the highest potential for safety improvement based on EPDO and excess expected crash frequency with forecasted future travel demand. The corridor will be studied further as part of the next stage in the regional planning process.

Exhibit 3. Example Application of the HSM in System Planning

Corridor Description

EPDO Score
(PDO crashes per year)

Excess Expected Average Crash Frequency
(fatal and injury crashes per year)

Route A, milepost 5.6 to 8.1

92

45

Route E, milepost 0 to 1.3

38

35

Route C, milepost 72.1 to 90.0

41

28