1. James H. Dunlop NCDOT Congestion Management Section
Congestion Management Options to Improve Air Quality
James H. Dunlop NCDOT Congestion Management Section

2. Ideal Driving Conditions

3. Usual Driving Conditions

4. A place where two or more roads meet
Intersections
A place where two or more roads meet

5. Conventional Intersection Conflict Points

6. Intersection Congestion
What is the traffic control device that leads to more confusion, congestion and air pollution than any other?

7. Intersection Congestion
The Traffic Signal

8. Signalized Intersections
The Purpose of a Traffic Signal is to take the Right-of- Way assignment away from the main flow of traffic and assign it to lesser movements

10. Main Street Green Time Main Phase ~ 70% Green Main Phase ~ 50% Green

11. Signalized Intersections
Eight-Phase Signal

12. Intersections
Does every intersection need every movement served at the same location?

13. Alternative Intersection Design Concepts
Separate conflicting movements
Reduce conflicts
Remove signals where possible
Limit phases at signalized intersections
Provide better signal coordination

14. Alternative Intersection Design Concepts
Roundabouts
Superstreets
Quadrant Lefts
Jughandles
Offset “T” Intersections
Continuous Flow Intersection

15. Circular Intersections
3 Types of Circular Intersections
Traffic Circle
Columbus Circle – New York City
Market Square - Fayetteville 15

16. Circular Intersections
3 Types of Circular Intersections
Traffic Circle
Traffic Calming Intersection

17. Circular Intersections
3 Types of Circular Intersections
Traffic Circle
Traffic Calming Intersection
Modern Roundabout
Clemmons, Forsyth Co.
NC State, Raleigh

18. Roundabout vs. Traffic Circle Size
Traffic Circle - ~ 800’ Diameter
Roundabout – ~ 180’ Diameter

19. Roundabout vs. Traffic Circle Deflection
Traffic Circle – 90 degree entry
Roundabout – degree entry

20. Roundabout vs. Traffic Circle Entry Traffic Control
Traffic Circle - Stop
Roundabout - Yield

21. Why Roundabouts? Safest Intersection High Capacity / Low Delay
Good for All Modes of Traffic
Geometric Flexibility
Aesthetics

22. Roundabouts - Safety
There are 32 conflict points at a conventional intersection.
There are only 8 conflict points at a modern roundabout

23. Crash Reductions Following Installation of Roundabouts
Roundabouts - Safety
Crash Reductions Following Installation of Roundabouts
In the United States – 2007
Total Crashes 48%
Fatal/Injury Crashes in Rural Areas 78%
Fatal/Injury Crashes in Urban Areas 60%
In North Carolina from
Conversion From Stop Sign Control 41%
Conversion From Signal Control 74%
Sources:
Insurance Institute For Highway Safety
NCHRP Report 572 onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_572.pdf
NCDOT Safety Evaluation Group

24. Roundabouts - Capacity and Operation
Peak Hour Traffic – Usually at least as efficient (same overall delay to drivers) as traffic signals or all-way stops
Off Peak Traffic – Usually much more efficient than traffic signals.
Multi-lane roundabouts can handle as much traffic as a busy signalized intersection

25. Roundabouts – Multi-Modal
Roundabouts provide a safer crossing for pedestrians

26. Roundabouts – Multi-Modal
Roundabouts provide safer travel for cyclists
PHOTOGRAPHY SOURCE: Lee Rodegerdts 26

27. Roundabouts – Multi-Modal

28. Roundabouts – Multi-Modal
Buses do not have trouble negotiating the roundabout, and provide a good location for bus stops

29. Large Trucks
PHOTOGRAPHY SOURCE: Lee Rodegerdts

30. Emergency Vehicles
PHOTOGRAPHY SOURCE: Brian Walsh

31. Roundabouts – Geometric Flexibility

32. Roundabouts – Geometric Flexibility
Roundabouts can be designed as ovals and oblong shapes in order to achieve better movement separation and accommodate unique intersection geometry
Works well for offset T-type and multiple legged intersections
Could be an option for median divided facilities where controlling access is an issue

33. Roundabouts – Geometric Flexibility
Corridor Operation

34. Landscaping

35. Landscaping
Bloomington, IN

36. Houten, the Netherlands
Landscaping
Houten, the Netherlands

37. Roundabout Air Emissions
At a roundabout replacing a signalised junction, CO emissions - 29% NOx emissions - 21% fuel consumption - 28%
At a roundabout replacing yield regulated junctions, CO emissions + 4% NOx emissions + 6% fuel consumption + 3%
“The results indicate that the large reductions in emissions and fuel consumption at one rebuilt signalised junction can “compensate for” the increase produced by several yield-regulated junctions rebuilt as roundabouts.”
The effects of small roundabouts on emissions and fuel consumption: a case study
András Várhelyi, Department of Technology and Society, Lund University, Sweden 2001

38. Roundabout Air Emissions
Better fuel efficiency and air quality
Where roundabouts replace signals, idling decreases which reduces vehicle emissions and fuel consumption by 30 percent or more.
(Minnesota DOT)

39. NY State Study Roundabout vs. Signalized intersection

40. Intersection Costs
Average Roundabout construction costs about $400,000
Maintenance is minimal (mostly mowing any additional landscaping is done by others)
Signalized intersection costs are about $100,000
Signal maintenance costs are about $3,000-5,000 annually
Construction of turn lanes is about $75,000-$150,000

41. North Carolina Roundabouts
Inventory as of August 2010

42. Single Lane Roundabouts
Clemmons, Forsyth Co.

43. Single Lane Roundabouts
NC State, Raleigh

44. Multi Lane Roundabouts
Davidson, NC
Griffith Street and
Davidson Gateway Drive
Griffith Street and Jetton Street

45. Superstreets
A type of intersection in which minor cross-street traffic is prohibited from going straight through or left at a divided highway intersection.
Minor cross street traffic must turn right, but can then access a U-turn to proceed in the desired direction.
*Other configurations possible based on site specific conditions.

47. Economically Beneficial Environmentally Responsible
Why Superstreets?
Improved Safety
Less Travel Time
Economically Beneficial
Environmentally Responsible

48. Why Superstreets? Improved Safety
Reduced conflict points (especially crossing movements) leads to reduced crashes

49. Superstreet Conflict Points
Total Conflict Points = 14
Improved Safety

50. Superstreet Benefits and Capacities (Research Project 2009-06)
Safety impact by collision type for unsignalized superstreets, %
Collision Type
Crash Reduction %
Total
-46
Fatal and injury
-63
Angle and right turns
-75
Rear ends -1
Sideswipes
-13
Left turns
-59
Other
-15 50

51. Why Superstreets? Less Travel Time Reduced “wait time” or delay
Increased roadway capacity
Improved signal coordination

52. Superstreet Phasing

53. Superstreets

55. Superstreet- US 321 Hickory-Lenoir
2035 Full Network Delay Analysis (Traditional Build vs. Three-lane Superstreet Build) AM PM
Traditional
Superstreet
% Change
Vehicles Exited (veh / hr)
31,760
35,618
12.15%
31,358
34,601
10.34%
Vehicles Entered (veh / hr)
33,730
37,283
10.53%
34,039
36,494
7.21%
Travel Distance (mi)
76,355
86,120
12.79%
73,721
82,465
11.86%
Travel Time (hr)
10,121
6,628
-34.52%
10,245
7,051
-31.17%
Total Delay (hr)
8,488
4,755
-43.98%
8,671
5,250
-39.45%
Total Stops (number)
111,713
122,511
9.67%
120,421
119,534
-0.74%
Fuel Usage (gal)
44,308
39,617
-10.59%
44,001
39,781
-9.59%
Per Veh. Distance (mi)
2.4
2.42
0.57%
2.35
2.38
1.38%
Per Veh. Time (hr)
0.32
0.19
-41.61%
0.33
0.2
-37.62%
Per Veh. Delay (hr)
0.27
0.13
-50.05%
0.28
0.15
-45.13%
Per Veh. Stops (number)
3.52
3.44
-2.21%
3.84
3.45
-10.04%
Per Veh. Fuel (gal)
1.4
1.11
-20.27%
1.15
-18.06%

56. 2009 – Looking south above Evans Road, PM peak
US 281 (San Antonio TX)
2009 – Looking south above Evans Road, PM peak

58. US 281 Superstreet Comments
As traffic congestion on U.S. Highway 281 eases due to the completion of the superstreet project, construction of new commercial and retail developments along the far North Central San Antonio corridor is ramping up.
“We are close to 90 percent leased with no pad sites left,” Elliott remarked. “We've had quite a bit of interest because of the market, which is in a high growth area. And a lot of our tenants say they feel like business has increased since the superstreet was finished.”
San Antonio Express-News March 17, 2011

59. Economically Beneficial
Why Superstreets?
Economically Beneficial
Preserves the existing facility
Less expensive than an interchange
Provides good access to both sides of the main road for development

60. UPS Expects To Save $600 Million by Favoring Right Hand Turns

61. Environmentally Responsible
Why Superstreets?
Environmentally Responsible
Less time spent idling at a red light
Reduction in environmental pollutants
(exhaust fumes / fuel usage)
Less acreage impacted by construction
and permanent facility

64. Superstreet-US 15-501 Chapel Hill

65. Superstreets US 15-501 Chapel Hill

66. Offset “T” Intersections
Two 3-Phase Signals Operate Better than an 8-Phase

67. Alternative Intersection Concepts
Don’t Allow the “Simple” Fourth Leg

68. What is a Quadrant Roadway?
A network of adjacent intersections that work together to relieve congestion at a busy intersection
Goal is to relieve one congested traffic signal with three or more simpler, less congested traffic signals
“Simpler” = fewer “phases” at signal

69. NC 73 Quadrant Roadway

70. Capacity Analysis Results 2030 Design Year Peak Periods
2030 Primary Network Delay Analysis (Full Movement vs. Quadrant Left) AM PM
Full Movement
Quadrant Left
% Change
Vehicles Exited (veh / hr)
6,127
7,736
26.26%
7,425
9,087
22.38%
Vehicles Entered (veh / hr)
6,234
7,774
24.70%
7,557
9,231
22.15%
Travel Distance (mi)
2,985
3,595
20.45%
3,512
4,256
21.19%
Travel Time (hr)
1,128
273
-75.81%
1,566
654
-58.22%
Total Delay (hr)
1,044
169
-83.86%
1,464
527
-63.99%
Total Stops
11,310
9,785
-13.48%
15,851
14,378
-9.29%
Fuel Useage (gal)
358
186
-48.01%
473
291
-38.59%
Per Veh. Distance (mi)
0.49
0.61
25.00%
0.29
0.35
19.52%
Per Veh. Time (hr)
0.20
0.04
-82.79%
0.21
0.07
-65.86%
Per Veh. Delay (hr)
0.17
0.02
-87.21%
0.06
-70.58%
Per Veh. Stops
1.85
1.26
-31.48%
2.13
1.58
-25.88%
Per Veh. Fuel (gal)
-58.83%
0.03
-49.82%

71. Jughandles
Main Street – No Lefts

72. Ingress and Egress Movements at Same Time
Left In/Out Access
Ingress and Egress Movements at Same Time

73. Left Turns Move During Same Phase as Throughs
Continuous Flow (CFI)
Left Turns Move During Same Phase as Throughs

74. Side Street Left Turn at Same Time as Main Left
Continuous Flow (CFI)
Side Street Left Turn at Same Time as Main Left

75. Continuous Flow (CFI)