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General Information on Roundabouts

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Unsignalised roundabouts provide a safe and efficient form of intersection control.  They have been used extensively in the Australia and Europe, and are being increasingly popular in the USA (where the term "modern roundabout" used).  This page provides information about modern roundabouts with an emphasis on capacity and level of service analysis methods.

Refer to the following publication for comprehensive information on roundabouts (available from the TRB and AUSTROADS websites):


TRB (2010). Roundabouts: An Informational Guide. NCHRP Report 672. Transportation Research Board, Washington, DC, USA.

TRB (2010). Highway Capacity Manual (HCM 2010). Transportation Research Board, National Research Council, Washington, DC, USA.

TRB (2016a). Highway Capacity Manual 6th Edition - A Guide for Multimodal Analysis. Transportation Research Board, National Research Council, Washington, DC, USA.

TRB (2016b). Roundabout Practices. A Synthesis of Highway Practice, NCHRP SYNTHESIS 488.  Transportation Research Board, Washington, DC, USA.

AUSTROADS - AGRD04B-15 (2015).  Guide to Road Design Part 4B: Roundabouts.  Association of Australian State Road and Transport Authorities, Sydney, Australia.


Roundabout Capacity Methods and Software

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Articles on Roundabouts

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Numerous articles on roundabouts can be found on our main Articles page.  Other articles reporting use of SIDRA INTERSECTION software for roundabouts and various other publications and web links are given in this page.

Improved Multi-lane Roundabout Designs for Cyclists.
CAMPBELL, D, JURISICH, I. and DUNN, R. Land Transport New Zealand Research Report 287. (11MB).

Pedestrian Safety in Strip Shopping Centres.
MIDSON, K. 3rd International Road Safety Conference, Perth, Australia.

RTA NSW Roundabouts Guide
A useful document on the use of multi-lane roundabouts.

Assessing the Clearwater Beach Entryway Roundabout.
SIDES. K. ITE 70th Annual Meeting Compendium 2000.  (790KB).

The Clearwater Beach Entryway Roundabout is on the island of Clearwater Beach, a project sited at the junction of the island's street network and the causeway carrying traffic from the mainland. Seasonal traffic volume varies from 30,000-58,500 vehicles per day. The beach district is a tourist destination, congested with drivers and pedestrians of all ages, bicyclists, rollerbladers and skate-boarders.  This impressive 6-leg 2-lane roundabout replaced nine existing intersections, three of which were signalized. Metering signals are used at this roundabout. 

Establishing Roundabout Guidelines for a State DOT.
KINZEL, C.S.  ITE 72nd  Annual Meeting Compendium 2002.

With the increasing popularity of roundabouts as a traffic control option, many State and local transportation agencies are in the process of developing guidelines and policies for the use of roundabouts within their respective jurisdictions. The purpose of this paper is to explore the process used, and the issues encountered, by the Missouri Department of Transportation in developing its statewide roundabout guide.  The paper states that "After much discussion, the committee decided that an initial check of roundabout capacity should be made using HCM procedures, but that SIDRA would be the required software for detailed operational analysis. The SIDRA software's increasing prevalence of use in the United States, and the committee's comfort level with a gap-acceptance-based analysis approach, were key factors in this decision."

Evaluation of Roundabout Performance Using SIDRA
Sisiopiku, V.P.  and OH, H.
ASCE Journal of Transportation Engineering 127 (2), 2001, pp 143-150.

Compares the performance of roundabouts with four leg intersections under yield control, two- and four-way stop control, and signal control for various traffic conditions using the SIDRA package.

Safety, delay, and capacity of single-lane roundabouts in the United States
Transportation Research Record 1646, pp 63-70. 1998.

A study of field-measured delays at single-lane roundabouts in the USA with those predicted by SIDRA concluded that "SIDRA can accurately predict delay for American single-lane roundabouts". 

Roundabouts:  The Round Solution Does not Always Fit the Square Problem
ITE District 6 Annual Conference, Las Vegas NV, 1999.

The purpose of this paper is to demonstrate that while roundabouts can offer solutions to traditional traffic engineering problems in some cases, they should not be proposed as the appropriate solution to all problems. Similar to any other potential traffic engineering solution, a variety of factors must be evaluated when considering roundabouts.

Roundabout Interchanges-So What Is The Real LOS?
ITE District 6 Annual Compendium 2002.

This paper presents the results of the various analysis procedures including SIDRA, HCM and micro-simulation under the same set of traffic volumes and parameters and the variation in results when a roundabout pair is evaluated as a system (roundabout interchange).

Roundabout studies in Kansas
RUSSELL, E. R., LUTTRELL, G. and and RYS, M.
Paper presented at the 4th Transportation Specialty Conference of the Canadian Society for Civil Engineering, Montreal, 2002.

Public Opinion and Traffic Flow Impacts of Newly Installed Modern Roundabouts in the United States
ITE Journal 72 (9), Sep 2002, pp 30-32,37.

The purpose of this study was to examine public opinion regarding roundabouts before and after construction in several US communities and to evaluate their impact on traffic flow. The results suggest that public support for roundabouts will build as drivers experience and adapt to this highly beneficial form of traffic control.

A Comparison of a Roundabout to Two-way Stop Controlled Intersections with Low and High Traffic Volumes.
ITE 70th Annual Meeting Compendium 2000.

A Kansas State University research team conducted a field study of the operation of the roundabout.  Comparison to similar traffic flows at stop controlled intersections were made. Using the measured field conditions as a starting point, the SIDRA computer model was used to evaluate a range of traffic conditions. SIDRA was used to replicate field conditions to test the roundabout and comparable two-way stop intersection operation at increasing traffic levels. Also see: Modeling Traffic Flows and Conflicts at Roundabouts

The Effects of Roundabouts on Pedestrian Safety
Prepared for the Southern transportation Centre, 2002. 

New Zealand Economic Evaluation Manual
Land Transport NZ's Economic evaluation manual is the industry's standard for the economic evaluation of roading projects and is used by approved organisations for project economic evaluation. The Manual sets out procedures and values to be used for the calculation of benefits such as savings in travel time, increased trip reliability, changes in vehicle operating costs, reduced accident costs, as well as benefits from increased road user comfort, reduced driver frustration and impacts on the environment and non-road users.

A formulation to evaluate capacity and delay of multilane roundabouts in the United States for implementation into a travel forecasting model.
Master of Science  in Engineering Thesis, The University of Wisconsin-Milwaukee, 2001.

Reintroducing roundabouts as a junction control device in Thailand
Taneerananon, P. and Intavichien, S.
Proc. of  the Eastern Asia Society for Transportation Studies, Vol. 3 No. 2, Oct 2001, pp 353-361.

Unbalanced traffic volumes at roundabouts
Fourth International Symposium on Highway Capacity, Transportation Research Circular E-C018, Transportation Research Board, 2000, pp 446-458.

Calibrating and validating traffic simulation models for unconventional arterial intersection designs
BOONE, J. L. and HUMMER, J. E.
Research Record 1500, Transportation Research Board, 1995, pp 184-192.

Unconventional traffic control alternatives including an application of the modern roundabout were examined using TRAF-NETSIM and SIDRA.  The validation effort showed that the TRAF-NETSIM and SIDRA results compared reasonably well to field measurements.

Modern roundabouts, global warming and emissions reductions: Status of research and opportunities for North America. 
Paper presented at the Canadian Transportation Research Forum, 36th Annual Conference, Vancouver, British Columbia, Canada, 2001.

Two decades of intersection modeling, software development and research, establish that substantial fuel savings at busy intersections can be gained by employing roundabouts rather than traffic signals.  Reduced fuel consumption and by extension pollution emissions are demonstrated through analysis of empirical data and modeling reported from existing US roundabouts and those under development.  

Analysis of pollutant emissions and concentrations at urban intersections
ITE 63rd Annual Meeting Compendium 1993.

Pollutant emissions were estimated using SIDRA for signal control and roundabout options at an intersection in Thessaloniki. Results indicated that emissions were higher under traffic signal control.

Other Useful Publications and Links on Roundabouts

Traffic Analysis Software Tools
Transportation Research Board Circular E-CO14, 2000.

Roundabouts: An Informational Guide
Publication No. FHWA-RD-00-067.  US Department of Transportation, Federal Highway Administration, McLean, Virginia, USA. 2000.

RTA NSW Roundabouts Guide

Pavement Marking of Roundabouts. 
Document No. TTT-029.  Traffic Technology Branch, Roads and Traffic Authority of New South Wales, Sydney, Australia.  1995.

Roundabouts - Geometric Design Method. 
Document No. TTT-033.  Traffic Technology Branch, Roads and Traffic Authority of New South Wales, Sydney, Australia.  1995. 

Roundabouts. Guide to Traffic Engineering Practice, Part 6.  AUSTROADS (Association of Australian State Road and Transport Authorities), Sydney, Australia.

Roundabout Photos

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Bend & Clearwater Roundabout Photos

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Australian Roundabout Photos

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