Abstract
Background:Roundabouts eliminate some of the most complex and dangerous aspects of traditional at-grade road intersections. In recent times, novel two-level roundabout layouts have been proposed (i.e. target-roundabout and four-flyover roundabout). Nevertheless, no research on underground roundabouts is available. This paper analyzed the underground roundabout planned in the city of Trento (Italy).Objective:The paper examines an underground roundabout in an urban context, planned with the purpose of alleviating traffic congestion in the city of Trento (Italy). Four different layouts have been studied.Methods and Results:This study was conducted with the help of traffic microsimulation in the AIMSUN environment. The traffic model was calibrated using GEH index. The simulated queues are significantly close to the real queues measured in the year 2020.Conclusion:Underground roundabout can reduce queues, travel times, fuel consumption, air pollutant emissionsetc. This particular type of roundabout could be used in urban contexts with a traffic demand and congestion problems comparable to those of the present study.
Highlights
The main advantage of roundabout intersections is due to the particular geometry that helps to decrease the frequency and severity of collisions by reducing the number of potential conflict points and constraining users to adopt moderate speeds [1 - 4].Many researchers observed a noteworthy decrease in accidents after transforming existing signalized and YIELD or stop-controlled intersections into roundabouts; only for example: Persaud [5] observed that the decrease in all accidents was 40% and the reduction in injury accidents was 80%; Troutbeck [6] observed a 74% reduction in injury accidents following the transformation of 73 roundabouts in Victoria, Australia.Roundabouts slow the speed of traffic streams and eliminate some of the most complex and dangerous aspects of conventional at-grade road intersections
This paper addresses the issue of underground roundabouts that are used only in some countries around the world (e.g. Norway and Switzerland, (Fig. 1)
It is noted that the introduction in the road network of the underground roundabout (Scenarios 3 and 4) with the right-turn bypass lane allows a significant density reduction, and traffic mean speed increases, compared to existing road configuration (Scenario 0)
Summary
Roundabouts slow the speed of traffic streams and eliminate some of the most complex and dangerous aspects of conventional at-grade road intersections. The operational speeds at multi-lane roundabouts are generally higher than those of single-lane roundabouts [7]. In this type of intersections, correct signs and pavement markings help to reduce speeds and crashes [3]. In the planning and designing phases, the safety performance of roundabouts can be estimated by Crash. Roundabouts eliminate some of the most complex and dangerous aspects of traditional at-grade road intersections. No research on underground roundabouts is available. This paper analyzed the underground roundabout planned in the city of Trento (Italy)
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