BACKGROUND

Self-explaining roads (SERs), also known as self-enforcing roads, use the design of the roadway itself to achieve the goals of a proactive and equitable Safe System Approach. SERs, designed to be recognizable, distinguishable, interpretable, and safe, can be effective in terms of managing speed, thereby reducing the occurrence of fatal and serious injury crashes. Two fundamental criteria a SER must meet are homogeneity (sameness) within and heterogeneity (differences) between roadway classifications and contexts to increase predictability within the road environment.

Roadway characteristics and competing stakeholder demands often undermine the application of design and operational characteristics and features, partially because the impacts of those features are not well understood, communicated, or implemented in the context of improving safety for all road users. A SER reinforces the desired functions of a facility by emphasizing visual differences between roadway categories that are often categorized by multimodal considerations and speed [e.g., 0-25 miles per hour (mph), 25-40 mph, 40+ mph].

Defining safe speeds and setting credible speed limits have a long history, with many studies exploring the impact of specific features on driver speed profiles, including the most recent ones such as NCHRP Research Report 966: Posted Speed Limit Setting Procedure and Tool: User Guide (2021) and FHWA-HRT-17-098 Self-Enforcing Roadway, A Guidance Report (2018). The vast but unconsolidated literature on speed lacks a format easily applicable by professionals in safety, planning, design, and operations.

This research is necessary to bridge the gap between the SER concept and its implementation in different functional classes and contexts, and identify the critical SER features so that practitioners can be more intentional and cognizant of the impacts of their decisions on all road users. Specifically, the final product of the project is expected to include recommendations that support active transportation and can be applied during the various phases of project development. These phases include geometric design, active transportation facilities, roadside design, land use, and traffic control devices, resulting in operating speeds that closely match target speeds.

OBJECTIVE

The objective of this research is to develop a guide for applying the SER concept to transportation planning, design, and operations to improve multimodal user safety, especially for vulnerable road users (VRUs) on nonfreeway arterial and collector systems in urban and suburban areas.