Reduced Environmental Impacts
By reducing vehicular delay through increased capacity and efficiency, the community will improve air quality through lowered emissions.
Driving through a typical intersection usually includes a complete stop, idling, then acceleration to proceed through the intersection.
With a roundabout, the stop may be eliminated, which reduces the fuel needed to re-accelerate.
The potential reduction in fuel consumption can increase in air quality. A KSU study found a significant reduction in emissions in before and after measurements.
|Measures of Effectiveness||Before||After||% Change|
|Source: Impact of Modern Roundabouts on Vehicular Emissions|
|Carbon Monoxide (CO) Kg/hr||10.79||7.26||-33%|
|Carbon dioxide (CO2) Kg/hr||237.30||127.59||-46%|
|Oxides of Nitrogen (NOx) Kg/hr||0.348||0.225||-35%|
|Hydrocarbons (HC) Kg/hr||.446||0.21||-53%|
The US Department of Transportation's Congestion Mitigation and Air Quality (CMAQ) Improvement Program provides funding for transportation projects aimed at reducing emissions levels. If a community is in air quality attainment, then those funds may be used for any project; if not, then those funds and others are directed to only projects related to bettering the air quality. Roundabouts help the community retain its project choice flexibility.