The Identification of Infrastructure Characteristics Influencing Travel Speeds on Single-carriageway Roads to Promote Self-explaining Roads

Road design characteristics should deliver a clear message to drivers on the appropriate speeds. This approach is known in the literature as "self-explaining roads" (SER). In Israel, new guidelines for setting speeds on the road network were introduced aiming at a balance between the target and actual travel speeds on various road types and, thus, supporting the SER concept. However, engineering tools are needed to implement the new approach. The purpose of this study was to explore the relationship between travel speeds and road infrastructure characteristics, on single-carriageway roads, aiming to identify the features influencing the travel speeds' selection by Israeli drivers. Statistical relations between road characteristics and speed indicators were explored using multivariate classification methods and regression models. The design speeds were reconstructed based on the infrastructure characteristics, and analyzed in relation to the travel speeds. Among the road characteristics most influencing the travel speeds were found: shoulder width and the recovery-zone width, where lower values of both characteristics were associated with lower speeds; junction density and road curvature, where higher presence of these characteristics had a moderating effect on speeds. It was concluded that changing shoulder width, recovery-zone width or junction density may be applied for promoting the SER concept and may affect travel speeds, yet a fine-tuning of existing design guidelines is required.