Editing Roundabout (section)

==== Capacity modelling ====
Many countries have researched roundabout capacity. The software can help calculate capacity, delay and queues. Packages include [[ARCADY]], Rodel, Highway Capacity Software and [[Sidra Intersection]]. ARCADY and Rodel are based on the Transport Research Laboratory mathematical model. The TRL approach is derived from empirical models based on geometric parameters and observed driver behaviour with regard to lane choice. Sidra Intersection software includes roundabout capacity models developed in Australia and the US.

Research on Australian roundabouts was conducted in the 1980s at the Australian Road Research Board (ARRB).<ref>{{cite book|url=http://www.arrb.com.au/Information-services/Publications.aspx|title=Effectiveness Audit of ARRB Intersection Capacity Research|location=Research Report ARR 242. ARRB Transport Research Ltd, Vermont South, Australia|author=Taylor, M.P., Barton, E.V., Bliss, J. and O'Brien, A.P. (1993)|url-status=dead|archive-url=https://web.archive.org/web/20160227020155/https://arrb.com.au/Information-services/Publications.aspx|archive-date=27 February 2016}}</ref> Its analytical capacity and performance models differ from the TRL model significantly, following a lane-based gap-acceptance theory including geometric parameters.

Research on U.S. roundabouts sponsored by the [[Transportation Research Board]] (TRB) and [[Federal Highway Administration]] (FHWA) culminated in a capacity model that was included in the ''[[Highway Capacity Manual]]'' (HCM) Edition 6<ref>{{cite book|url=http://www.trb.org/publications/hcm6e.aspx|title=Highway Capacity Manual, Sixth Edition: A Guide for Multimodal Mobility Analysis|author=TRB (2016)|location= Transportation Research Board, National Research Council, Washington, DC, US}}</ref> and the ''TRB-FHWA Roundabout Informational Guide'' ([[NCHRP]] Report 672).<ref>{{cite book|url=http://www.trb.org/Main/Blurbs/164470.aspx|title=Roundabouts: An Informational Guide |author=TRB|date=2010 |location=NCHRP Report 672. Transportation Research Board, National Research Council, Washington, D.C., US, in cooperation with US Department of Transportation, Federal Highway Administration|doi=10.17226/22914 |isbn=978-0-309-15511-3 }}</ref> The HCM Edition 6 model is based on lane-based gap-acceptance theory. A recent NCHRP survey of US state transport agencies found that [[Sidra Intersection]] is the most widely used software tool in the US for roundabout analysis.<ref>{{cite book|url=https://www.nap.edu/catalog/23477/roundabout-practices|title=''Roundabout Practice, A Synthesis of Highway Practice''|publisher=  Transportation Research Board|year=2016|location=National Cooperative Highway Research Program, NCHRP SYNTHESIS 488. Washington DC, US.|doi=10.17226/23477|isbn=978-0-309-27208-7 |last1=Pochowski |first1=Alek |last2=Paul |first2=Andy |last3=Rodegerdts |first3=Lee A. }}</ref>