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Characterizing the Relationship between Carbon Dioxide Emissions and Vehicle Operating Modes on Roundabouts -A Pilot Test in a Single Lane Entry Roundabout

Shaojie Liu, Qing Li, Fengxiang Qiao, Jianbang Du and Lei Yu

Roundabouts were initially installed to improve traffic flow and safety. However, the reduction may be not only limited to the idling duration. This research attempts to characterize the relationship between CO₂ emissions and vehicle’s operating modes on a roundabout. An on-board emission pilot test was conducted on a one-lane-entry roundabout with four legs between Westcott Street and Washington Avenue in Houston, Texas, during peak and nonpeak hours of two consecutive weekdays. The test vehicle was a two-year old gasoline vehicle, which was equipped with a Portable Emission Measurements System (PEMS) to detect real-time exhaust emission rates from the tailpipe and estimate fuel consumption rates. A Global Positioning System (GPS) with magnetic force was placed on the roof of the vehicle to record vehicle’s dynamic geolocation, while an On-board diagnostic (OBD) II port was connected to the test vehicle collected real-time vehicle operation information, such as speeds. Results showed that 35 km/h approaching speed could minimize the CO₂ emissions. Hard acceleration can lead to a spike in the CO₂ emissions, while speeding by frequent small acceleration is beneficial to control the emissions. The longer route within the roundabout is in favor of fewer CO₂ emissions. The vsp between 0 and 9 kw/ton and speed between 1.6 km/h and 40.2 km/h (1-25 mph) are identified as the typical feature of the vehicle operations on the roundabout.