1. At-Grade Intersection

2. Types of Intersection Maneuvers
Source: FHWA Roundabout Guide

3. 32 4-way Intersection conflict points  High speed impacts
 High angle impacts
SAFETY
This a 4-way intersection, just like all the ones you drove through coming here today.
The lines are the paths cars take
The dots are CONFLICT POINTS where paths cross and cars collide
Most of the dots are in the middle
<CLICK>. There are total of 32 conflict points
<CLICK>. That’s also where the high-speed,
<CLICK>. high-angle crashes occur, which are the most lethal

4. Motor Vehicle conflicts
Roundabout 8
conflict points
75% reduction in
Motor Vehicle conflicts
 Low speed impacts
SAFETY
This is a roundabout.
The circulating lane
The path of entering cars
<CLICK>
There are only 8 CONFLICT POINTS
<CLICK>. That’s 75% reduction in conflict points
No other design produces such a large reduction in conflict points
<CLICK>. All conflicts are LOW SPEED impacts, due to the slow speeds of Roundabout
<CLICK>. All conflicts are LOW ANGLE merge impacts, due to the geometrics of Roundabout
 Low angle impacts

5. BEFORE
AFTER

11. Intersection Control Hierarchy
No Control (Basic Rule)
Yield Sign
Stop Sign – normal control method
All-Way Stop
Roundabout
Traffic Signal
Grade Separation

12. Traffic Signals Advantages Orderly movement of traffic
Reduces certain types of crashes
Interrupts heavy flows for minor movements
Promotes driver confidence
Provides gap for minor movements
When properly designed and located

13. Traffic Signals Disadvantages
Increases total delay, especially off-peak
Increases fuel consumption
Increases crashes
Induces road users to less appropriate routes
Unnecessary delay if not properly located
Bad timing, bad engineer!

14. GRADE SEPARATION
High flows
Minimal delays
Expensive

15. At-Grade Railway Crossings
Horizontal alignment
Intersection at right angle on a tangent section
No other nearby intersections
Vertical alignment
Intersection as level as possible
Adequate view of crossing
Vertical profile should prevent vehicles with low clearance from being caught on the track (see below)

22. Traffic Lane

23. Auxiliary Lanes

24. Auxiliary Lanes Auxiliary lanes:
remove accelerating or decelerating vehicles from the through lanes
store turning vehicles
increase road capacity
Types of acceleration or deceleration lanes
parallel lanes
directional lanes (tapers)

25. Auxiliary Lanes Tapers
MEDIAN
MEDIAN

26. Lane Shift

32. Offset Left-Turn Lanes

33. Offset Left-Turn Lanes

34. Continuous Left-Turn Lanes

35. Minimum Design for U-Turns Exhibit 9-92

38. Objectives of Channelization and Design Elements to Achieve Them

46. Design of Channelizationq

47. Design of Channelization

48. Design of Channelization

49. Design of Channelization

50. Design of Channelization

51. Design of Channelization (Type 1)

52. Design of Channelization (Type 1)

53. Design of Channelization

54. Design of Channelization (Type 2)

55. Design of Channelization (Type 2)

56. Design of Channelization

57. Design of Channelization (Type 3)

58. Design of Channelization (Type 3)

59. Design of Channelization

60. Design of Channelization (Type 4)

61. Design of Channelization (Type 4)

62. Design of Channelization

63. Design of Channelization

64. Traffic Island

69. Simultaneous Left-Turn Lanes
Exhibit 9-99

70. Corner Cut

76. Appendix

83. Sight Obstruction
Hidden Vehicle

84. Auxiliary Lanes

85. Continuous Left-Turn Lanesm

86. Offset Left-Turn Lanes

87. Traffic Island