THE TRAFFIC CAPACITY OF ROUNDABOUTS

A study has been made of the entry capacities of conventional and offside priority roundabouts at eighty-six public road sites, and a unified formula for capacity prediction developed. The traffic flow entering a roundabout from a saturated approach was found to be linearly dependent on the circulating flow crossing the entry. The most important factors influencing the capacity are the entry width and flare. The entry angle and radius have small but significant effects. The inscribed circle diameter, used as a simple measure of overall size, is more effective as a predictive variable for the capacity than the category distinction between conventional and offside priority roundabouts, and for capacity prediction there is no need to retain this distinction. In addition to normal capacity prediction, methods have been developed which allow: (I) the predictive equation to be corrected to take account of local operating conditions at overloaded existing sites; and (II) the equation to be used specifically to predict the effects of changes in the entry geometry of existing sites. (Author/TRRL)

• Corporate Authors:

  Transport and Road Research Laboratory (TRRL)

  Wokingham, Berkshire  United Kingdom 
• Authors:
  • KIMBER, R M
• Publication Date: 1980

Media Info

• Features: Figures; References; Tables;
• Pagination: 43 p.

Subject/Index Terms

• TRT Terms: Access roads; Beltways; Building entrances; Equations; Forecasting; Geometric design; Highway capacity; Intersection elements; Layout; Mathematical models; Offside; Roundabouts; Traffic congestion; Traffic flow
• Uncontrolled Terms: Entrances
• Old TRIS Terms: Entrances (Other than doors)
• ITRD Terms: 435: Access road; 643: Capacity (road, footway); 632: Congestion (traffic); 426: Entrance; 132: Forecast; 2885: Layout; 6473: Mathematical model; 9053: On the left; 438: Roundabout; 671: Traffic flow
• Subject Areas: Design; Highways; Operations and Traffic Management; Planning and Forecasting; I21: Planning of Transport Infrastructure; I71: Traffic Theory; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 00324338
• Record Type: Publication
• Source Agency: Transport Research Laboratory
• Report/Paper Numbers: TRRL LR942 Monograph
• Files: ITRD, TRIS, ATRI
• Created Date: Sep 16 1981 12:00AM