Before-and-After Field Investigation of the Effects on Pollutant Emissions of Replacing a Signal-Controlled Road Intersection with a Roundabout

Table 1

Summary of selected studies comparing vehicular emissions at intersections under different types of control (numbers in first column correspond to cited references) [4].

Reference	Method for estimation of emissions	Pollutants considered	Main findings
[6, 7]	Emission factors for observed speeds and accelerations	CO,	Emissions for small RBT are lower than for SIG and slightly higher than for UNSIG.
[8]	Instrumented vehicle	CO, CO2,	Results are dependent on local conditions and time of day; emissions tend to be generally lower for RBT than for SIG and higher for RBT than for UNSIG.
[9]	aaSIDRA 2.0 software	CO, CO2, HC,	Emissions are reduced following conversion of stop-controlled intersections to RBTs.
[10]	aaSIDRA 2.1 software	CO, CO2, HC,	Emissions of all considered pollutants are lower for RBT than for AWSC. They are also lower for RBT than for SIG, but only up to a threshold of total intersection demand volume.
[11]	VISSIM software	CO, , VOC	Converting TWSC into RBT can reduce vehicle emissions under most traffic volume scenarios.
[12]	INTEGRATION and VISSIM software; VT-Micro and CMEM emission models	CO, CO2, HC,	Emissions of all considered pollutants are higher for RBT than for SIG and TWSC.
[13]	Paramics software; MOVES and CMEM emission models	CO,	Emissions of considered pollutants are higher for RBT than for SIG under both light and congested traffic conditions.
[14]	Instrumented vehicle	CO, CO2, HC,	Emissions for RBT are often higher than for SIG and AWSC. Strong effect of driver behavior on emissions.
[15]	INTEGRATION software	CO, CO2, HC,	Emissions of CO, HC, and are generally lower for RBT than for SIG and UNSIG; results for CO2 are dependent on overall demand and turning ratios.
[16]	S-Paramics and AIRE software	, PM10, Total Carbon	Emissions for RBT are slightly lower than for SIG.
[17]	Vehicle-specific power and observed speed trajectories	CO, CO2, HC,	Results of comparison of emissions for RBT and SIG depend on demand-to-capacity ratio and on quality of signal progression.
[18]	VISSIM software; vehicle-specific power and EMEP-EEA emissions methodologies	CO, CO2, HC, , PM	For a sequence of intersections along an arterial, emissions are lower for RBT than for SIG and higher for RBT than for TWSC.

RBT: roundabout; SIG: signal-controlled intersection; UNSIG: unsignalized intersection; AWSC: all-way stop-controlled intersection; TWSC: two-way stop-controlled intersection; EMEP-EEA: European Monitoring and Evaluation Programme–European Environment Agency.