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James H. Dunlop NCDOT Congestion Management Section. Congestion Management Options to Improve Air Quality. Ideal Driving Conditions. Usual Driving Conditions. Intersections. A place where two or more roads meet. Conventional Intersection Conflict Points. Intersection Congestion.

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james h dunlop ncdot congestion management section
James H. DunlopNCDOTCongestion Management Section

Congestion Management Optionsto Improve Air Quality

slide4

Intersections

A place where two or more roads meet

slide6

Intersection Congestion

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

slide7

Intersection Congestion

The Traffic Signal

slide8

SignalizedIntersections

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

slide10

Main Street Green Time

Main Phase ~ 70% Green

Main Phase ~ 50% Green

Main Phase ~ 33% Green

slide11

Signalized Intersections

Eight-Phase Signal

slide12

Intersections

Does every intersection need every movement served at the same location?

slide13

Alternative Intersection Design Concepts

  • Separate conflicting movements
  • Reduce conflicts
  • Remove signals where possible
  • Limit phases at signalized intersections
  • Provide better signal coordination
slide14

Alternative Intersection Design Concepts

  • Roundabouts
  • Superstreets
  • Quadrant Lefts
  • Jughandles
  • Offset “T” Intersections
  • Continuous Flow Intersection
slide15
Circular Intersections

3 Types of Circular Intersections

  • Traffic Circle

Columbus Circle – New York City

Market Square - Fayetteville

slide16

Circular Intersections

3 Types of Circular Intersections

  • Traffic Circle
  • Traffic Calming Intersection
slide17

Circular Intersections

3 Types of Circular Intersections

  • Traffic Circle
  • Traffic Calming Intersection
  • Modern Roundabout

Clemmons, Forsyth Co.

NC State, Raleigh

slide18
Roundabout vs. Traffic CircleSize

Traffic Circle - ~ 800’ Diameter

Roundabout – ~ 180’ Diameter

slide19
Roundabout vs. Traffic CircleDeflection

Traffic Circle – 90 degree entry

Roundabout – 45-60 degree entry

slide20

Roundabout vs. Traffic CircleEntry Traffic Control

Traffic Circle - Stop

Roundabout - Yield

slide21

Why Roundabouts?

  • Safest Intersection
  • High Capacity / Low Delay
  • Good for All Modes of Traffic
  • Geometric Flexibility
  • Aesthetics
slide22

Roundabouts - Safety

There are 32 conflict points at a conventional intersection.

There are only 8 conflict points at a modern roundabout

slide23

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 Areas60%

In North Carolina from 1999-2006

      • Conversion From Stop Sign Control 41%
      • Conversion From Signal Control 74%

Sources:

Insurance Institute For Highway Safetywww.highwaysafety.org

NCHRP Report 572 onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_572.pdf

NCDOT Safety Evaluation Groupwww.ncdot.org/doh/preconstruct/traffic/safety/Reports/completed.html

slide24

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
slide25

Roundabouts – Multi-Modal

  • Roundabouts provide a safer crossing for pedestrians
slide26

Roundabouts – Multi-Modal

  • Roundabouts provide safer travel for cyclists

PHOTOGRAPHY SOURCE: Lee Rodegerdts

slide28

Roundabouts – Multi-Modal

  • Buses do not have trouble negotiating the roundabout, and provide a good location for bus stops
slide29

Large Trucks

PHOTOGRAPHY SOURCE: Lee Rodegerdts

slide30

Emergency Vehicles

PHOTOGRAPHY SOURCE: Brian Walsh

slide32

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
slide35
Landscaping

Bloomington, IN

slide36
Landscaping

Houten, the Netherlands

slide37

Roundabout Air Emissions

At a roundabout replacing a signalised junction, CO emissions - 29% NOxemissions - 21% fuel consumption - 28%

At a roundabout replacing yield regulated junctions, CO emissions + 4% NOxemissions + 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

AndrásVárhelyi, Department of Technology and Society, Lund University, Sweden 2001

slide38

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.

http://www.dot.state.mn.us/roundabouts/

(Minnesota DOT)

slide40

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
slide41

North Carolina Roundabouts

Inventory as of August 2010

slide42
Single Lane Roundabouts

Clemmons, Forsyth Co.

slide43
Single Lane Roundabouts

NC State, Raleigh

slide44

Griffith Street and

Davidson Gateway Drive

Griffith Street andJetton Street

Davidson, NC

Multi Lane Roundabouts

slide45

Superstreets

  • Minor cross street traffic must turn right, but can then access a U-turn to proceed in the desired direction.
  • A type of intersection in which minor cross-street traffic is prohibited from going straight through or left at a divided highway intersection.

*Other configurations possible based on site specific conditions.

slide47
Improved Safety

Less Travel Time

Economically Beneficial

Environmentally Responsible

Why Superstreets?

slide48

Why Superstreets?

Improved Safety

Reduced conflict points (especially crossing movements) leads to reduced crashes

slide49

Superstreet Conflict Points

Total Conflict Points = 14

Improved Safety

superstreet benefits and capacities research project 2009 06
Superstreet Benefits and Capacities(Research Project 2009-06)

Safety impact by collision type for unsignalized superstreets, %

slide51

Why Superstreets?

Less Travel Time

  • Reduced “wait time” or delay
  • Increased roadway capacity
  • Improved signal coordination
slide56

US 281 (San Antonio TX)

2009 – Looking south above Evans Road, PM peak

slide58

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

slide59

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
slide61

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
slide66

Offset “T” Intersections

Two 3-Phase Signals Operate Better than an 8-Phase

slide67

Alternative Intersection Concepts

Don’t Allow the “Simple” Fourth Leg

slide68

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 ormore simpler, less congested traffic signals
  • “Simpler” = fewer “phases” at signal
slide71

Jughandles

Main Street – No Lefts

slide72

Left In/Out Access

Ingress and Egress Movements at Same Time

slide73

Continuous Flow (CFI)

Left Turns Move During Same Phase as Throughs

slide74

Continuous Flow (CFI)

Side Street Left Turn at Same Time as Main Left