Treatment Effects and Design Guidance for High- to Low-Speed Transition Zones for Rural Highways

This paper presents the results of a study to develop improved design guidance for high- to low-speed transition zones on rural highways. The primary steps of the research included a literature review and state-of-practice review on speed reduction treatments used in transition zones and observational field studies of several transition zone treatments in the United States. The principal findings from the observation field studies are that roundabouts and transverse pavement markings increase the rate of compliance of vehicles traveling at or below the speed limit at the end of a transition zone by 15% and 20%, respectively, as compared with no treatment. Roundabouts increase the rate of compliance of vehicles traveling within 5 mph (8 km/h) of the speed limit at the end of a transition zone by 11%, compared with no treatment. The findings support previous research that indicates the need to provide additional measures through the community to maintain speed reduction downstream of the transition zone through the community. This paper also addresses several issues to be considered in the design of high- to low-speed transition zones, including definitions and site characteristics of the geographical limits or boundaries of the transition zone study area; a methodology for assessing whether a high- to low-speed transition zone has speed limit compliance or safety issues to support the need for, and the selection of, an appropriate treatment to address the issues; and guiding principles and design concepts to be considered in the design of a transition zone.