1 Channelization and Turn Bays

2 Island Channelization flush, paved, and delineated with markings – or unpaved and delineated with pavement edge and markings raised … use lighting raised rural … also delineate and slope curbs Size: large enough to command attention Must delineate a path that is natural and convenient for the driver

3 Island Channelization Must have sufficient approach sight distance to islands Curb radii – appropriate for necessary island size (25 m or 75 feet at least) see exhibits 9-41 and 9-42 if used at series of rural intersections, keep geometry consistent see exhibit 9-35 for common use

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6 Consider left turn lane if advancing volume/percent left combination exceeds these values. For left turn volume > 300 VPH, consider dual left turn lane.

7 Channelization – Functional Objectives Limit Conflict Points (i.e., prohibit certain movements, non-overlap of opposing LTs), esp. in vicinity of intersection functional area (see figures) Limit Conflict Area Complexity (i.e., eliminate legs, add turn lanes, islands) Limit Conflict Frequency (i.e., add turn lanes, use right angles) Limit Conflict Severity (i.e., small angles, adequate turn bay length/curb radii for speed differential issues)

8 Principles of Channelization 1. Undesirable/wrong-way movements should be discouraged 2. Vehicle paths clearly defined 3. Desirable/safe speeds encouraged 4. Separation of conflict points if possible 5. Cross at right angles, merge at flat angles 6. High priority traffic facilitated 7. Desired traffic control schemes facilitated 8. Remove slow, stopped, or decelerating vehicles from traffic stream 9. Provide safe refuge for peds and others

9 Intersection Islands Definition – “a defined area between traffic lanes for control of vehicle movements or pedestrian refuge” Types/functions: Directional – “to control and direct movement” and “to guide motorists into the proper channel for their intended route”

10 Divisional – “to divide opposing traffic flow”, and “to alert the driver to the crossroad ahead and regular traffic through the intersection” Refuge – “to aid and protect pedestrians and bicyclists crossing the roadway”

11 Intersection Turn Bays New Construction Warrants (functional approach): all unstopped approaches on primary, high speed rural highway intersections with other primary roadways, see fig Other approaches where through, left, and opposing volumes justify “Where space permits, left-turn lanes should be considered when left-turn volumes exceed 100 vph…” (Green Book)

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13 Rehabilitation Warrants: Typically installed where there is a safety issues with vehicles turning left Guides for need – See figure 4-12 and Exhibit 9-75 Lane width: 12 ft. (new) and 11 ft. or greater for rehab, see figure 4-5

14 40mph

15 50mph

16 Length required

17 Design

18 Design

19 Design

20 1. Left Turn Bay Length: a) PRT & 10 MPH reduction occurs upstream of bay (more in congested, urban conditions) see fig b) accommodate deceleration from D.S. – 10 mph to stop, see table 5-8 c) Unsignalized, accommodate 2 minutes of demand, at least 2 cars (or 1 car and 1 truck if truck% > 10), see figure 5-15 or 4-18 d) Signalized, accommodate twice the expected average storage needed – depends on cycle and phasing, see figure 5-14 e) Right turn bay length depends on corner radius, see fig. 4-24

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27 Turn Bay Components (see fig 4-14) 1. Approach taper 2. Bay Taper 3. Full lane Length 4. Departure Taper 5. Shadow width

28 Some Turn Lane Details 1. Transitions are often symmetrical reverse curves or straight line (see Exhibit 9-95) – curves at each end are desirable - Lengths and radii given in the same figure 2. For tapers: see figure Green Book: 8:1 to 15:1 tapers for high speed highways … urban use 100’ for single and 150’ for dual left turn lane

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31 Striping through Intersection: Difficult to See

32 Curb Radius Parking Lot

33 Island for No Left Turn

34 Right Turn Bay Curve

35 Left Turn Bay Taper

36 Left Turn Separated

37 Left Turn Bay (No Transition)

38 Left Turn Bay Pavement Markings

39 Curb Radius Curb Cut

40 Turn Lane Pedestrian Refuge

41 Curb Cut

42 RR Crossing

43 RR Crossing Raised Median

44 Right Turn Island

45 Island Pedestrian Refuge

46 Median End Treatment

47 Left Turn Bay Curve, Right Turn Bay Taper

48 Left Turn Bay Circular Transition

49 Median to Discourage U-Turns

50 3 Leg Intersection

51 Median End (Keep Right)

52 Median End Delineation

53 Median in front of Lowes

54 Intersection Approach Lincoln Way at Elwood

55 Intersection Approach 4 th at Elwood Drive

56 Median: Elwood Dr. at Airport Rd.

57 Points of Conflict Traffic conflicts occur where the path of traffic movement crosses.

58 T-Intersection or Driveway Side Street Two Lane Undivided Street

59 T-Intersection or Driveway Side Street Two Lane Undivided Street

60 4-Way Intersection or Driveway 2 lane streets Note: Add 4 conflicts to each for four lane roadways 40 conflicts with Four Lane on major street

61 Limit Conflicts - Objectives Limit Conflict points Limit Conflict Area Complexity Limit Conflict Frequency Limit Conflict Severity

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65 T-Intersection or Driveway After #1 Two lane roadway with raised median closed, no left-turn

66 4-Way Intersection or Driveway After #1 Added median close eliminates left-turn conflicts

67 T-Intersection or Driveway After #2 Two lane roadway with raised median (left turn egress only from intersection or driveway)

68 4-Way Intersection or Driveway After #2 Two lane roadway with raised median (left turn egress only from intersection or driveway)

69 T-Intersection or Driveway After #3 Two lane roadway with raised median (left turn ingress only into driveway)

70 4-Way Intersection or Driveway After #3 Two lane roadway with raised median (left turn ingress only into intersection or driveway)

71 Two Way Left Turn Lanes at Intersection or Driveway: Two way left turn lanes (TWLTL) (3 lane roadway) Reduces rear-end accidents and allows merging traffic to store in TWLTL

72 Pedestrian Refuge Island at Intersection for TWLTL

73 Urban Intersection

74 Urban Channelized Intersection-

75 Raised Median: Clive

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