The first modern, single lane roundabout on an arterial in Missoula opened in August, 2009.   Compared to signals, the severity of crashes has been very low.  It is estimated that 1,000 tons of CO2 have been saved (2009-2018), due to less idling of motor vehicles when compared to a stop light.  MIST is advocating that the geometry of the roundabout be modified for tighter turns.  This change would reduce speeds, thus improving both capacity and safety.