Environmental impact of modern roundabouts

In United States (US) vehicular emissions have increased considerably over the years and have attracted the attention of environmental and transportation researchers. Traditional intersections force vehicular traffic to slow down and stop in varying patterns and contribute to the increase in vehicular emissions. Modern roundabouts in US have enhanced the performance and safety of many intersections. There are numerous studies conducted by IIHS and various researchers, which support this fact. These modern roundabouts are not only capable of improving traffic flow but they can as well cut down vehicular emissions and fuel consumption by reducing the vehicle idle time at intersections and thereby creating a positive impact on the environment. The primary focus of this research was to study the impact of modern roundabouts in cutting down vehicular emissions. Six sites with different traffic volume ranges, where a modern roundabout has replaced stop-controlled intersection, have been chosen for the study. The operation of the roadways at the intersection was videotaped and the traffic flow data was extracted from these tapes and analyzed using SIDRA (signalized and un-signalized intersection design and research aid) software. The version used was aaSIDRA 2.0. The software produces many Measures of Effectiveness (MOEs) of which four were chosen for analyzing the environmental impact of roundabouts. The chosen four outputs give rate of emission of HC, CO, NOX and CO2 in (kg/h). All the MOEs were statistically compared to determine which intersection control performed better. After comparing all the MOEs at all locations for the before and after traffic volumes, it was found that the modern roundabout performed better than the existing intersection control (i.e. stop signs) in cutting down vehicular emissions therefore creating a positive impact on the environment. The research concludes that a modern roundabout can be used as a viable alternative to cut down vehicular emissions, making intersections more environmentally friendly. (C) 2007 Elsevier B.V. All rights reserved.