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 PDF Document
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.