00756242

Component

https://doi.org/10.3141/1646-08

http://scholar.google.com...dden&publication_year=1998

Roundabouts are a form of at-grade intersection control that is used frequently around the world and is becoming popular in the United States. Roundabouts are being used to replace two-way and all-way stop-controlled intersections and traffic signals in the United States. Roundabouts have also been used recently in Vail, Colorado, to improve an existing stop-controlled freeway interchange system. In this study, five single-lane roundabouts are studied to assess their safety and operational performance. All five sites were stop-controlled before roundabouts were installed, and overall the sites experienced a reduction in accident frequencies, rates, and also control delay. Aside from a review of safety and delay data before and after installation of the roundabouts, this study includes a comparison of field-measured control delay with that predicted by SIDRA, an analytically based software package that can analyze at-grade sign- and signal-controlled intersections as well as roundabouts. This study will help agencies better understand their ability to predict delay at American roundabouts. Finally, findings are presented regarding the accuracy of the roundabout capacity model contained in the 1997 update to Chapter 10 of the "Highway Capacity Manual". Because of the lack of roundabout entries that are operating at capacity in the United States, an approximation of potential capacity based on available gaps in the circulating stream was made. These findings indicate that the manual may be optimistic in its prediction of capacity for single-lane roundabouts in the United States; however, it should be noted that the lack of roundabout entries operating under capacity in the United States only allows for an approximation of field capacity to be made at this time.

This paper appears in Transportation Research Record No. 1646, Highway Capacity Issues 1998.

English

p. 63-70

1998

Transportation Research Record

0309065186

Figures (4) ; Photos (3) ; References (10) ; Tables (5)

Accuracy; Alternatives analysis; Before and after studies; Crash rates; Field studies; Forecasting; Highway capacity; Operations; Safety; Single lane traffic; Software; Traffic circles; Traffic delays

Highway Capacity Manual

Field data; Operational analysis

Administration and Management; Highways; Operations and Traffic Management; Safety and Human Factors; I71: Traffic Theory

TRIS, TRB, ATRI

Nov 18 1998 12:00AM

• ACCURACY AND PERFORMANCE OF IMPROVED SPEED-FLOW CURVES
• ANALYSIS OF TWO LEFT-TURN EQUATIONS FROM THE "HIGHWAY CAPACITY MANUAL"
• BACKGROUND FOR HCM SECTION ON ANALYSIS OF PERFORMANCE OF ROUNDABOUTS
• DETERMINING IMPACT OF ROAD LIGHTING ON MOTORWAY CAPACITY
• EFFECT OF BICYCLES ON CAPACITY OF SIGNALIZED INTERSECTIONS
• EFFECT OF PEDESTRIANS ON CAPACITY OF SIGNALIZED INTERSECTIONS
• ESTIMATION OF PERCENTAGE OF DELAYED VEHICLES BASED ON TRAFFIC VARIABLES FOR RURAL HIGHWAYS
• EXTENSION AND APPLICATION OF PROSSER-DUNNE MODEL TO TRAFFIC OPERATION ANALYSIS OF OVERSATURATED, CLOSELY SPACED SIGNALIZED INTERSECTIONS
• FIELD MEASUREMENT OF SIGNALIZED INTERSECTION DELAY FOR 1997 UPDATE OF THE "HIGHWAY CAPACITY MANUAL"
• GAP ACCEPTANCE CAPACITY FOR RIGHT TURNS AT SIGNALIZED INTERSECTIONS
• NEW ESTIMATION TECHNIQUE FOR VEHICLE-TYPE-SPECIFIC HEADWAY DISTRIBUTIONS
• PHASE CAPACITY CHARACTERISTICS FOR SIGNALIZED INTERCHANGE AND INTERSECTION APPROACHES
• QUEUEING AT CONGESTED INTERSECTIONS
• SIMPLE, GENERALIZED METHOD FOR ANALYSIS OF TRAFFIC QUEUE UPSTREAM OF A BOTTLENECK
• SIMULATION STUDIES OF TRAFFIC OPERATIONS AT OVERSATURATED, CLOSELY SPACED SIGNALIZED INTERSECTIONS