# Photovoltaic Roundabouts for Enhancement of Self-Sufficiency and Resiliency
###### Abstract  
Roundabouts have become a common type of intersection design in many countries. The area of the center island can be used to install a photovoltaic system to power local loads such as lighting systems. The objective of this study is to evaluate the degree of self-sufficiency that a roundabout can achieve depending on the availability of the area for the installation of a photovoltaic system and the energy demand for lighting. The methodology is divided into five steps aimed at calculating the parameters required to characterize the roundabouts from the point of view of the electricity that can be generated by the photovoltaic systems installed, and then to evaluate the energy consumption required to operate the different system solutions for lighting. The mini roundabouts are not considered as a location for the photovoltaic system; in fact, the minimum diameter must be between 29 and 34 m. Considering the available irradiance in Italy, systems with monocrystalline silicon modules are sufficient to ensure energy self-sufficiency at diameters of 24 m or more. Systems with polycrystalline silicon modules are suitable to ensure energy self-sufficiency at diameters of 25/26 m or more. Photovoltaic (PV) technology continues to make progress in increasing efficiency, such as bifacial PV modules. This means that even smaller roundabouts could be eligible for a PV system sized to meet local electricity needs. photovoltaic technology; monocrystalline silicon; polycrystalline silicon; energy demand; electricity productivity; street illumination; roundabout design +
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Lighting is perhaps of greater interest for the modern roundabout than for any other type of highway intersection because it has unique design features, such as raised splitter islands with flared ends at the exits/entrances to the circulatory roadway and a raised center island with a radius large enough to divert traffic from the approaches into the roundabout. These features are important to reduce speeds and prevent or significantly reduce fatal and serious crashes at roundabouts. However, when travelling at night, these features must be visible, or they can become a potential source of danger to motorists. In addition, because the deflection of the roadway into the roundabout lane, a vehicle's headlight beam is often tangential to the roundabout lane and does not illuminate objects and/or colliding movements from the left side of the vehicle. This means that drivers are often looking into the darkness when entering the roundabout. Therefore, the overall safety of a roundabout at night can be improved by dedicated street lighting [17, 18]. Lighting of a roundabout can be accomplished by installing lighting poles in the center island or at the edge of the intersection. Lighting at the edge of the roundabout provides the best visibility of key areas and visibility of circulating vehicles to vehicles approaching the roundabout. In addition, vertical lighting levels in crosswalks can only be achieved if approach lighting is used. Therefore, roundabouts with central island lighting may require additional approach lighting or may be combined with outdoor lighting to achieve the vertical lighting level. Figure 1 shows the significant differences in center island and circulatory roadway lighting between central and perimeter lighting. Both illumination designs include approach lighting. Worldwide, there are several normative references that regulate the illuminance for roundabouts. Most European countries have adopted the European Union standard, EN 13201 (hereafter EN), in its entirety or with some modifications, as the basis for lighting their roundabouts. Consisting of four parts, EN has been adopted by the European Committee for Standardization since 2003 (Modus 2012) and contains both warnings and standards for roadway and intersection lighting. Table 1 summarizes the European Standard (EN 13201-2:2016) recommended illuminance levels for roundabouts located in continuously illuminated roads [19].