Safety Data and Analysis in Developing Emphasis Area Plans

SECTION I - Introduction

In 1998, AASHTO approved its Strategic Highway Safety Plan, with a goal of reducing annual highway fatalities by 5,000 to 7,000. The plan includes strategies in 22 key emphasis areas that affect highway safety. NCHRP Project 17-18(3) is developing a series of guides to assist state and local agencies in reducing injuries and fatalities. Each guide is focused on one of the key emphasis areas (e.g., head-on collisions, unsignalized intersection collisions, collisions involving unlicensed drivers, collisions involving pedestrians). Each emphasis-area guide includes a brief introduction, a general description of the problem, the strategies/countermeasures to address the problem, and a model implementation process. The guides are published as individual volumes within NCHRP Report 500: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan (1—20), and copies can be obtained from the Transportation Research Board and downloaded from .

In addition to the individual emphasis area guides, NCHRP Report 501: Integrated Management Process to Reduce Highway Injuries and Fatalities Statewide provides an overall framework for coordinating a safety program. The integrated management process comprises the necessary steps for advancing from crash data to integrated action plans. The process includes methodologies to aid the practitioner in problem identification, resource optimization, and performance measurements.

A series of meetings with "lead states" was held in 2004— 2005 to test the first sets of NCHRP Report 500 volumes produced. The lead states used the guidance documents in the development of emphasis-area plans. Technical assistance was provided to those states during that process under the NCHRP 17-18(3) project. Issues raised by those states during that process led to the development of additional supplemental resources, including example plans for lane-departure and intersection crash issues. These plans contained detailed example data analysis procedures that the states could use in choosing strategies/countermeasures within an emphasis area and in targeting those treatments to roadway locations. Similar procedures for roadway-user and vehicle emphasis areas (e.g., older drivers, large trucks) were not developed at that time. It was subsequently decided that an additional guide would be produced to assist state and local users in locating and analyzing pertinent safety data in their planning effort for any of the 22 emphasis areas. The purpose of the "Data and Analysis Guide" is to provide guidance on the sources of safety data needed and on procedures for both choosing the best strategies/countermeasures within a given emphasis area and targeting those treatment strategies to either roadway locations or road-user subgroups.

There are many steps and procedures necessary to successfully plan and implement safety strategies within a given emphasis area. Many of these steps are related to developing the critical "safety team" of administrators, planners, program managers and analysts. These procedures are covered in detail in both the model implementation plans within each of the NCHRP Report 500 volumes, and within NCHRP Report 501 (18). While those procedures covered the entire safety-planning process, this "Data and Analysis Guide" is focused on the procedures and steps necessary in the datarelated efforts involved in emphasis-area planning. The procedures were developed to be applicable in jurisdictions that have extensive safety data files (e.g., crash, roadway inventory, intersection inventory, traffic) and limited safety data (i.e., crash data only), and both for situations in which the crash-related effectiveness of a specific countermeasure has been defined and situations where countermeasure effectiveness is unknown at this time. The guide addresses emphasis-area safety planning for situations in which relevant crash data are available to guide the planning process. Safety planning for situations in which no crash data are available is outside the scope of this guide. However, safety managers should be aware that there are important emphasis areas, including pedestrian and bicycle safety, for which safety plans often need to be developed without crash data or with very limited crash data. The guide does suggest data types that are potentially useful in safety plan development, as a supplement to crash data or when crash data are not available.

This guide addresses the development of safety plans for specific emphasis areas, but does not address the evaluation of the effectiveness of those plans after their implementation. For evaluation issues, the reader is referred to NCHRP Report 501(18) and to specific safety evaluation tools such as Safety Analyst.

The goals of this guide are the following.

• Specify a basic three-stage procedure to be used in developing an emphasis area plan: (1) choosing an area, (2) setting a goal, and (3) choosing among potential strategies within the given area and targeting their implementation to subpopulations of road users, vehicle types, or roadway locations.
• Define data-related procedures for roadway, road user, and vehicle-based emphasis areas that will assist the user in the third stage — choosing among potential treatment strategies and targeting the strategies.
• Define procedures which can be used with three levels of safety data and treatment effectiveness:
  • Known treatment effectiveness combined with linkable crash, roadway inventory and traffic data
  • Known treatment effectiveness and crash data only (e.g., no inventory data)
  • Unknown treatment effectiveness and crash data only
• Customize the procedures and data descriptions for different groups of emphasis areas (e.g., lane departure crashes, special road-user populations including older and younger drivers, pedestrians and bicyclists).

The following text will provide an overview of the proposed data analysis procedures to be covered in this guide. Descriptions of potential safety data files for use in these and other procedures will be presented in Section II of the guide. General details of the procedures will be presented in Section III. The procedures will then be customized for specific groups of emphasis areas in Sections IV—XI. Finally, information on improving existing databases will be presented in Section XII.

Introduction to Proposed Procedures

As indicated above, the development of a safetyimprovement plan is a multi-stage process. (For clarity, the term "stage" will be used to describe the major procedures required to develop the plan. The term "step" will then be used to describe individual steps/processes required to conduct a given major stage/procedure. Thus, there are "steps" within "stages.")

Stage 1. Define/Choose Issue(s)/Emphasis Areas
The safety planning team will first define or choose an issue (emphasis area) or set of issues that need to be addressed. Note that the AASHTO Strategic Highway Safety Plan and all of the supporting resources (e.g., NCHRP Report 501) intend that multiple issues should be addressed and multiple plans developed. The guide deals with addressing one issue at a time, but the procedures will be applied multiple times to address all issues of interest. As described later, the choice will most often be based on analysis or crash data which assist the user in determining which of the 22 issues/areas defined by AASHTO or additional jurisdiction-specific issues are most critical in his or her jurisdiction.

Stage 2. Set a Crash, Injury or Death Reduction Goal for That Issue
The emphasis-area team will then use a series of factors to define a reduction goal for death and injuries in each of the emphasis areas chosen. AASHTO has suggested that a "stretch goal" be established for both the overall safety program composed on a combination of emphasis areas, and within a given emphasis area. This "stretch goal" is one that is not likely to be met by existing safety efforts, or even a limited expansion of these efforts. The goal will push the jurisdiction to be innovative in defining new programs and procedures to achieve success. The agency may decide to define both a "stretch goal" and a series of reduced or lesser goals that can be met either within a given time period or with innovative, but realistic, efforts.

Stage 3. Define the Series of Treatments and the Target Subpopulation (Drivers, Highway Corridors, Intersections) for Each Treatment That Will Be Required to Meet Your Goal
The goal of this step is to develop a combination of treatment strategies and targets which will allow the user to meet the established goal. In general, this will require the following steps.

1. Define possible subpopulations (e.g., drivers, miles of specific highway types, intersection types in specific highway classes) for treatment.
2. Specify one or more proposed treatments for each target subpopulation.
3. If treatment effectiveness is known, determine if the number of targets (e.g., miles/drivers/intersections) that can be treated in each subpopulation will lead to reductions that meet the specified goal. If not, add additional treatments or new target populations (e.g., local roads if the original targets were on the state system).
4. If possible, determine whether the benefits derived from treating the target subpopulations exceed the costs. (Note that this assurance that the treatment is cost beneficial does not have to be a separate step. With processes presented later in this guide, it can be done during the definition of target subpopulations if "full data" are available and if treatment effectiveness is known. This benefit-cost calculation will not be possible for treatments without defined effectiveness levels.)
5. If a treatment for a specific subpopulation is not costeffective, consider other possible treatments with higher crash-reduction potential, consider alternative targets (e.g., local road systems if you are a state DOT), or consider ways to reduce the cost of the treatment implementation (e.g., combine roadway safety treatment with other non-safety work at chosen locations, piggy-back public information campaign onto scheduled enforcement activities).
6. If cost-effective, implement the treatment(s)!

Note that all these steps may have to be done interactively until a final solution is reached. In addition, they may not be done in the sequence shown here. For example, as noted above, the final definition of target subpopulations may be done before the determination of strategies, and may also be done concurrently with the determination of B/C ratios, depending on the methodology used. The following sections will provide more specific guidance concerning this overall procedure tailored to the different types of emphasis areas.