Article Transportation Research Record 2018, Vol. 2672(25) 21–34 Ó National Academy of Sciences: Transportation Research Board 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0361198118774667 journals.sagepub.com/home/trr The Potential of Metering Roundabouts: Influence in Transportation Externalities Paulo Fernandes 1 , Joa ˜o Teixeira 1 , Claudio Guarnaccia 2 , Jorge M. Bandeira 1 , Eloı ´sa Macedo 1 , and Margarida C. Coelho 1 Abstract Roundabouts are increasingly being used on busy arterial streets for traffic calming purposes. However, if one roundabout leg is near a distribution hub, for example, parking areas of shopping centers, the entry traffic volumes will be particularly high in peak hours. This paper investigated a partial-metering-based strategy to reduce traffic-related costs in a corridor. Specifically, the resulting traffic performance, energy, environmental, and exposure impacts associated with access roundabouts were studied in an urban commercial area, namely: (a) to characterize corridor operations in terms of link-specific travel time, fuel consumption, carbon dioxide and nitrogen oxides emissions, and noise costs; (b) to propose an optimization model to mini- mize these outputs; and (c) to demonstrate the model applicability under different traffic demand and directional splits com- binations. Traffic, noise, and vehicle dynamics data were collected from a corridor with roundabouts and signalized intersections near a commercial area of Guimara ˜es, Portugal. Microscopic traffic and emission modeling platforms were used to model traffic operations and estimate pollutant emissions, respectively. Traffic noise was estimated with a semi-dynamical model. Link-based cost functions were developed based on the integrated modeling structure. Lastly, a sequential quadratic programming-type approach was applied to find optimal timing settings. The benefit of the partial-metering system, in terms of costs, could be up to 13% with observed traffic volumes. The efficiencyof the proposed system increased as entering traf- fic at the metered approaches increased (~7% less costs). The findings enable quantification of metering benefits near shop- ping areas. Previous studies have demonstrated the commercial, healthy environment, and safety benefits of replacing sig- nalized corridors with functionally interdependent roundabouts near commercial locations (1, 2). Consequently, some authorities have adopted round- abouts in series along corridors (3, 4), some of these located near business and commercial areas. Nevertheless, some evidence suggests roundabouts may reach saturation under moderate traffic volumes (5). Unbalanced flows among legs may not be a problem when the overall demand level is low. However, if one leg of a roundabout provides access to parking areas of shopping mall, the entry volumes of the corresponding approach will be high. This fact may increase delay on the next approaches, resulting in unnecessarily long queues and congestion (6). Among possible solutions, such as changing round- about design, implementing other forms of intersection, or installing metering signals, the latter strategy is the most cost-effective measure (5). Metering signals regulate flow into the circulating area of roundabouts from one approach and thereby create larger gaps for downstream entries, thus alleviating vehicle delays on roundabout legs (7). Full-time and partial-time metering strategies can be adopted. Roundabouts with full leg-by-leg con- trol are not suitable for these cases as approaches must split in few seconds after signals are implemented (8). In turn, partial metering can control a specific roundabout leg (7) during heavy demand periods and optimize delay for other legs. Design guidelines available for transportation plan- ners to implement metering signal systems at round- abouts are lacking. Applications of metered roundabouts have been mostly conducted in Australia, the United Kingdom, and in the United States (7). Typically, traffic lights are installed on roundabout approaches, but a second stop line to control left-turning traffic can be adopted (9). In this context, Fahmy 1 Department Mechanical Engineering/Centre for Mechanical Technology and Automation (TEMA), University of Aveiro, Aveiro, Portugal 2 Department of Civil Engineering, University of Salerno, Fisciano (SA), Italy Corresponding Author: Address correspondence to Paulo Fernandes: paulo.fernandes@ua.pt