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Comparison of Safety Performance Models for Urban Roundabouts in Italy and other Countries

TRB Transportation Research Board of the National Academies
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In Italy, almost half of all road crashes occur at intersections, mostly in urban areas. However in recent years the widespread conversion of signalized intersections to roundabouts has brought many advantages in terms of safety. To assess safety benefits of this kind of intersection, transportation professionals need the powerful statistical tool known as the Safety Performance Function (SPF). To date there has been no reported application of this tool to assess the relative safety performance of Italian urban roundabouts. Thanks to the availability of data sets from the Municipalities of Novara and Trento (Northern Italy), SPFs were estimated with the negative binomial error distribution, and their transferability between cities was evaluated with the recalibration procedure being implemented in the Highway Safety Manual. In particular, the evaluation of the models was done with the Cumulative Residuals (CURE) method. To assess how the Italian situation might be used to learn lessons from differences in crash experience for similar intersections elsewhere, a comparison with roundabout models from other countries is also provided

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