The US Department of Transportation (USDOT) and the Federal Highway Administration (FHWA) has released some information regarding the roundabout. Here are some of the highlights. Most accidents occur at channelized, high speed, right angle intersections. Roundabouts remove left hand turns, which are the most dangerous traffic maneuver, deflecting and slowing speeds in a circular manner, resulting in a 90% reduction in fatalities and a 35% reduction in all crashes. Roundabouts move a higher volume of traffic than a standard traffic signal (see Myth Busters link below). Economically speaking roundabout often have a higher installation cost but lower maintenance cost over the lifetime of the infrastructure. Environmentally roundabouts are "greener" with reduced emissions from reduced idling times. Roundabouts are able to accommodate large delivery trucks and emergency services with "truck aprons".
Concerning nonmotorized users roundabout are safer for pedestrians because they only need to cross one direction of traffic, and often fewer lanes, and they have a "splitter" or pedestrian island refuge. Cyclists may choose to dismount and use the roundabout as a pedestrian or in a vehicular fashion. Helena has existing roundabouts on the outskirts such as the South Helena Interchange that have proved successful, with a future one in the planning process at Lincoln Road and Green meadow. The Green America's Capitals plan suggested a roundabout as a solution a "Mini-Malfunction Junction". This option would use the existing right-of-way, so additional lanes would not be required. Have the citizens Helena come around on this safer, more efficient, and environmental alternative to the standard traffic signal?
Additional examples of roundabout in Montana include the recently installed roundabout in Great Falls at the Montana Department of Transportation Headquarters. Also the the series of roundabout on Shiloh Ave in Billing leading to the airport.
USDOT FHWA Us Department of Transportation Federal Highway Administration short film
Modern Roundabouts: A Safe Choice
http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10023/transcript/audio_no_speaker/
http://www.youtube.com/watch?v=uhHzly_6lWM
Additional resource
Myth Busters: 4 Way Stop vs. the Roundabout
http://www.youtube.com/watch?v=OvoFjirrgYA
