The geometric design of a modern roundabout is an iterative process which aims for a balance between design objectives such as safety, capacity, costs of construction, and maintenance requirements, as well as environmental and aesthetic impacts. Among roundabouts, turbo-roundabouts represent an alternative model, which provides a spiraling traffic flow and requires drivers to choose their direction before entering the intersection, limiting lane changing, and driving speed since raised lane dividers mark entry, circulating, and exit lanes. Turbo-roundabouts are now used worldwide in view of the benefits in traffic safety, and their construction has induced a great variety of experiences. Since only a few studies were based on field data or have calibrated specific models for turbo-roundabouts, academics and practitioners have been using microscopic traffic simulation to predict turbo-roundabout performance.

The goal of this special issue is to verify the effect of geometric parameters and traffic-related determinants on the performance of turbo-roundabouts and to provide a collection of scientific improvements focusing on analysis, design, and operation of turbo-roundabouts. Even though turbo-roundabouts have been well accepted, their impact on the safety, capacity, and environmental emission modeling has not been sufficiently studied, and many challenges and research themes are still open, including how to choose between turbo-roundabouts and modern roundabouts in the context of a system-wide resource allocation process; how to develop a capacity model where patterns of conflict at entries with one and two conflicting traffic streams coexist; which is the most appropriate type of turbo-roundabouts according to the main characteristics of the traffic demand; how to examine conditions under which a safety and performance analysis at turbo-roundabouts could be independent of the software used; and how to assess the future changes to traffic flow characteristics that may derive from automated vehicles; and how to implement computational strategies to increase efficiency in intelligent infrastructure management.

This special issue welcomes original research and review articles addressing all aspects of turbo-roundabout design geared toward solving the questions above.

Potential topics include but are not limited to the following:

• Planning and design of turbo-roundabouts in multimodal transport networks under various environmental constraints
• Effect of geometric parameters on turbo-roundabout performance
• Driver behavior analysis during turbo-roundabout crossing
• Analysis of traffic safety performance of turbo-roundabouts and sustainability in transit and traffic operations
• Entry-lane capacity modeling and simulation through optimization
• Estimation of safety performance using historical crash data, surrogate measures of safety, and traffic conflicts
• Closed-form models for estimating efficiency of turbo-roundabouts
• Design treatments for heavy vehicles at turbo-roundabouts
• Comparison of safety levels of turbo-roundabouts with different values of geometric parameters and their optimization
• Contributions for calibration and validation of capacity, safety, and emission prediction models for turbo-roundabouts
• Safety and vulnerability of road users