Background

The U.S. Department of Transportation (USDOT) has designated improved pedestrian and bicyclist safety as a top priority. The Federal Highway Administration (FHWA) and other federal agencies routinely work with state and local agencies to provide technical resources, develop analytical approaches, and highlight best practices to improve the safety and connectivity of bicycling and walking networks. Part of this effort has been to promote a data-driven approach to identifying and mitigating safety problems. Various data sets and analytic approaches have been developed to improve the quality and analysis of pedestrian and bicyclist crash data.

Pedestrian and bicyclist exposure to risk is often mentioned as a missing piece of the puzzle. The lack of readily-available pedestrian and bicyclist exposure data often make it difficult to accurately identify and then prioritize high-crash (or high-risk) locations or interpret year-to-year trends in citywide, state, or national crash statistics. Even when pedestrian or bicyclist exposure data are used, inconsistency can be present in the formulation and calculation of exposure measures between regions. Exposure has been defined based on direct counts, population, hours of travel, miles of travel, and others. Having different exposure measures and definitions make direct comparisons difficult, if not impossible. If pedestrian and bicyclist safety analyses were to use a consistent exposure measure (such as the number of street crossings or the number of pedestrian or bicyclist trips), then direct comparisons among studies and analyses would be much easier and meaningful.

Pedestrian and bicyclist exposure is also a critical element in better understanding pedestrian and bicyclist crash causation. For example, exposure is a key variable in developing pedestrian and bicyclist safety performance functions, which are used to identify those factors that best predict when and where crashes are likely to occur. If exposure is not included, then the effects of other factors may be biased or overstated due to the omission of a key variable (exposure).

In early 2016, FWHA published the Final Rule on the Highway Safety Improvement Program (HSIP) and Safety Performance Management Measures (www.fhwa.dot.gov/safety/legislative-safety-programs/spm). The Final Rule does require that state DOTs and metropolitan planning organizations (MPOs) report five safety management performance measures, one of which is the number of non-motorized fatalities and non-motorized serious injuries. Since two of the motorized safety performance measures include exposure (i.e., 100 million vehicle miles traveled), there was consideration about whether to include exposure in the non-motorized measure. However, several comments on the Draft Rule expressed concern about the lack of suitable non-motorized exposure data, and therefore the Final Rule does not include exposure in the non-motorized safety performance measure.

Overall Project Objectives

In May 2016, the FHWA’s Office of Safety initiated this project to develop a standardized approach to estimate pedestrian and bicyclist exposure to risk in the form of a Scalable Risk Assessment Methodology (ScRAM). This approach will make it easier to assess pedestrian and bicyclist exposure to risk and inform project priorities and funding decisions, and will include several methods according to the scale of the needed exposure estimate.  The project objectives are three-fold:

1. Synthesize and document existing resources that agencies can use to assess pedestrian and bicyclist exposure to risk.
2. Develop scalable risk assessment methods for practitioners to use to calculate pedestrian and bicyclist exposure to risk that can be applied to a facility, corridor, network/system, or regional level. The risk assessment methods are likely to include separate but parallel modules for estimating pedestrian and bicyclist exposure.
3. Widely promote the use of these risk assessment methods through outreach, training, and technical assistance.

Task 3 Objectives

This report documents the findings of Task 3, which sought to review and synthesize the variety of methods used to estimate and evaluate exposure in pedestrian and bicyclist safety analyses (i.e., first objective in bullet list above). Later tasks in this project will develop and promote the risk and exposure assessment methods (i.e., second and third objectives in bullet list above). This report differentiates between exposure on a network or regional basis and exposure on specific transportation facilities (e.g., a street crossing or mid-block link).

Report Overview

This report includes the following chapters:

• Chapter 1. Introduction: Summarizes the need for risk exposure measures and outlines the overall project objectives and the specific objective of Task 3.

• Chapter 2. Definitions and Concepts: Outlines basic definitions and concepts for risk and exposure, and then discusses these terms in the context of pedestrian and bicyclist safety analysis.

• Chapter 3. Exposure Analysis at Areawide Levels: Summarizes the use of exposure measures at areawide levels, and describes the data sources and methods that could be used for exposure measures at these more aggregate analysis levels.

• Chapter 4. Exposure Analysis on Specific Transportation Facilities: Summarizes the use of exposure measures on specific transportation facilities (e.g., street crossings, street segments) and describes the data sources and methods that could be used for exposure measures at these more granular analysis levels.

• Chapter 5. Risk Factors Other Than Exposure: Outlines the variety of risk factors (other than exposure) that affect pedestrian and bicyclist safety.

• Chapter 6. Conclusions: Develops and summarizes conclusions based on the findings of the synthesis of practice and literature review.