1. ROUNDABOUT CHARACTERISTICS TTE 6815

2. DEFINITIONS TRAFFIC CIRCLE: u Any intersection designed around a central island ROUNDABOUT: u A traffic circle with certain prescribed characteristics

5. ROUNADBOUT BENEFITS n Community enhancement n Traffic Calming n Safety n Reduced delay at lower volumes n Improved left turn treatment n Complex intersections

6. CURRENT ISSUES n Ped/bicycle treatment n High capacity applications n Residential street applications n Visibility requirements n Design details n Cost of implementation

7. ROUNDABOUT CHARACTERISTICS n Yield on entry

8. ROUNDABOUT CHARACTERISTICS n Yield on entry

10. ROUNDABOUT CHARACTERISTICS n Entry deflection for speed control

11. ROUNDABOUT CHARACTERISTICS n Yield on entry n No internal control n Entry deflection for speed control Deflection Min Radius = 100 m Min Radius = 100 m

12. ROUNDABOUT CHARACTERISTICS n No parking on circulating roadway

13. ROUNDABOUT CHARACTERISTICS n No parking on circulating roadway

14. ROUNDABOUT CHARACTERISTICS n No pedestrians on center island

15. ROUNDABOUT CHARACTERISTICS n Counter clockwise circulation

16. ROUNDABOUT CHARACTERISTICS n Counter clockwise circulation

17. ROUNDABOUT CHARACTERISTICS n Counter clockwise circulation

18. ROUNDABOUT CHARACTERISTICS n Counter clockwise circulation

19. ROUNDABOUT CHARACTERISTICS n Must accommodate design vehicle

23. ROUNDABOUT CHARACTERISTICS n Splitter islands

24. ROUNDABOUT CHARACTERISTICS n Splitter islands

25. ROUNDABOUT CHARACTERISTICS n Splitter islands

26. ROUNDABOUT CHARACTERISTICS n Pedestrians cross one car length back from the entry point

27. ROUNDABOUT CHARACTERISTICS n Pedestrians cross one car length back from the entry point

28. ROUNDABOUT CHARACTERISTICS n Pedestrians cross one car length back from the entry point

29. ROUNDABOUT CHARACTERISTICS n Deflection by physical features

30. ROUNDABOUT CHARACTERISTICS n Deflection by physical features

31. ROUNDABOUT CHARACTERISTICS n Deflection by physical features

32. OTHER REQUIREMENTS n Easily identified in the road system. n Layout must be clearly visible and must encourage drivers to enter slowly. n Adequate lighting is necessary.

33. A SIMPLE YIELD CONTROLLED JUNCTION n Because a roundabout is a series of yield-controlled junctions, this provides a good place to start.

34. n Press F7 to see these graphics of the intersection layout.

35. TRAFFIC VOLUMES n 60 % EB n 40% NB n Start with … u 300 EB u 200 NB

36. FIRST SIDRA RUN n Set up the basic parameters and intersection configuration n Enter traffic volumes n Enter flow scale limit at 250% n Run SIDRA n Observe performance measures

37. VOLUME GROWTH FACTOR n 100% TO 250 % n Capacity reached at 242% u 726 vph EB u 484 vph NB u NB Delay = 42 sec/veh

38. VOLUME GROWTH FACTOR v/c Ratio

39. VOLUME GROWTH FACTOR v/c Ratio Delay

40. VOLUME GROWTH FACTOR Capacity

41. VOLUME GROWTH FACTOR Capacity Spare Capacity

42. n CAPACITY: 484 n V/C RATIO :.40 n DELAY: 41.7 s/v n STOP RATE: 2.7 n 95% BACK OF QUEUE: 26.1 veh

43. TRAFFIC VOLUMES n 60 % EB n 40% NB n Now Try… u 675 EB u 450 NB n About 85% v/c

44. SECOND SIDRA RUN n Enter new volumes n Disable flow scale n Run SIDRA n Observe performance measures

45. n NB Delay: 19.2 sec/veh MOVEMENT CAPACITY AND PERFORMANCE SUMMARY --------------------------------------------- Mov’t Arv Total Deg. Aver. Eff. 95% Flow Cap. Satn Delay Stop B.O.Q ---------------------------------------------- EBT 675 1800 0.375 0.0 0.00 0.0 --------------------------------------------- NBR 450 530 0.849* 19.2 1.97 15.5

46. NEXT... n Let’s make up a roundabout composed of four of these junctions n Entering Volume 450 vph n Circulating Volume 675 vph

48. HOW?... n Each LT is included in the circulating volume at 2 junctions n Each Thru movt is included at 1 junction n RT’s do not appear anywhere

49. SO... n 450 vph on each approach n 60% Left (270 vph) n 30% Thru (135 vph) n 10% Right (45 vph)

50. CIRCULATING VOLUME 270 x 2 = 540 135 x 1 =135 === Total675

53. THIRD SIDRA RUN n Set up the roundabout configuration n Enter new volumes n Run SIDRA n Compare the performance with a single YIELD junction

54. COMPARISON n YIELD V/C =.85 Del = 19.2 s/v n ROUNDABOUT V/C =.64 Del = 9.3 s/v

55. ROUNDABOUT GAP ACCEPTANCE PARAMETERS ------------------------- Turn Critical Follow Gap Up (s) Headway ------------------------- Left 4.43 2.49 Thru 4.43 2.49 Right 4.43 2.49 -------------------------

56. STOP & YIELD CONTROL GAP ACCEPTANCE PARAMETERS Crit. Fol.up Min. % Exit Flow Gap Hdway Deps Opposing Left turns : 7.0 3.40 1.0 50 Through : 6.5 3.30 1.0 50 Right turns: 5.5 2.60 1.0 50 Opposed turns from priority road: 5.5 2.60 1.0 0

57. FOURTH SIDRA RUN n Return to YIELD example n Change gap acceptance characteristics n Run SIDRA n Observe performance measures

58. YIELD control with roundabout gap acceptance parameters n V/C Ratio =.646 n Delay = 7.6 s/v

60. FIFTH SIDRA RUN n Change island diameter to 4 meters and rerun SIDRA n Change island diameter to 100 meters and rerun SIDRA n Compare performance measures

61. EFFECT OF CENTRAL ISLAND DIAMETER 4 METERS n C. G. = 4.72 n F.O.H = 2.65 n V/C =.696 n Del = 11.6 100 METERS 4.14 sec 2.32 sec.575 7.4 sec/veh