James H. DunlopNCDOT

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

What is the traffic control device that leads to more confusion,

congestion and air pollution than any other?

Intersection Congestion

The Traffic Signal

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

Signal Timing - Eight PhaseSignal Timing - Three PhaseSignal Timing - Two Phase

Main Street Green Time

Main Phase ~ 70% Green

Main Phase ~ 50% Green

Main Phase ~ 33% Green

Signalized Intersections

Eight-Phase Signal

Intersections

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

Alternative Intersection Design Concepts

Separate conflicting movements

Reduce conflicts

Remove signals where possible

Limit phases at signalized intersections

Provide better signal coordination

Roundabouts

Superstreets

Quadrant Lefts

Jughandles

Offset “T” Intersections

Continuous Flow Intersection

Alternative Intersection Design Concepts

3 Types of Circular Intersections

Traffic Circle

Circular Intersections

Columbus Circle – New York City

Market Square - Fayetteville

3 Types of Circular Intersections

Traffic Circle

Traffic Calming Intersection

Circular Intersections

3 Types of Circular Intersections

Traffic Circle

Traffic Calming Intersection Modern Roundabout

Clemmons, Forsyth Co. NC State, Raleigh

Circular Intersections

Roundabout vs. Traffic CircleSize

Traffic Circle - ~ 800’ Diameter

Roundabout – ~ 180’ Diameter

Roundabout vs. Traffic CircleDeflection

Roundabout – 45-60 degree entry

Traffic Circle – 90 degree entry

Traffic Circle - Stop

Roundabout - Yield

Roundabout vs. Traffic CircleEntry Traffic Control

Why Roundabouts? Safest Intersection

High Capacity / Low Delay

Good for All Modes of Traffic

Geometric Flexibility

Aesthetics

There are 32 conflict points at a conventional intersection.

There are only 8 conflict points at a modern roundabout

Roundabouts - Safety

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 1999-2006

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

Sources:Insurance Institute For Highway Safety www.highwaysafety.orgNCHRP Report 572 onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_572.pdfNCDOT Safety Evaluation Group www.ncdot.org/doh/preconstruct/traffic/safety/Reports/completed.html

Roundabouts - SafetyCrash Reductions Following Installation of Roundabouts

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

Roundabouts -

Capacity and Operation

Roundabouts provide a safer crossing for pedestrians

Roundabouts – Multi-Modal

PHOTOGRAPHY SOURCE: Lee Rodegerdts

Roundabouts – Multi-Modal

Roundabouts provide safer travel for cyclists

Roundabouts – Multi-Modal

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

Roundabouts – Multi-Modal

PHOTOGRAPHY SOURCE: Lee Rodegerdts

Large Trucks

PHOTOGRAPHY SOURCE: Brian Walsh

Emergency Vehicles

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

Roundabouts – Geometric Flexibility

Corridor Operation

Roundabouts – Geometric Flexibility

Landscaping

Landscaping

Bloomington, IN

Landscaping

Houten, the Netherlands

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 studyAndrás Várhelyi, Department of Technology and Society, Lund University, Sweden 2001

Roundabout Air Emissions

Better fuel efficiency and air qualityWhere 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)

Roundabout Air Emissions

NY State Study Roundabout vs. Signalized intersection

• 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

Intersection Costs

North Carolina Roundabouts

Inventory as of August 2010

Clemmons, Forsyth Co.

Single Lane Roundabouts

NC State, Raleigh

Single Lane Roundabouts

Multi Lane Roundabouts

Griffith Street and Davidson Gateway Drive

Griffith Street andJetton Street

Davidson, NC

• 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.

Superstreets

Improved SafetyLess Travel Time

Economically BeneficialEnvironmentally Responsible

Why Superstreets?

Reduced conflict points (especially crossing movements)

leads to reduced crashes

Improved Safety

Why Superstreets?

Improved Safety

Total Conflict Points = 14

Superstreet Conflict Points

Superstreet Benefits and Capacities(Research Project 2009-06)

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

Safety impact by collision type for unsignalized superstreets, %

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

Less Travel Time

Why Superstreets?

Superstreet Phasing

Superstreets

2035 Full Network Delay Analysis (Traditional Build vs. Three-lane Superstreet Build)  AM PM  Traditional Superstreet % Change Traditional Superstreet % ChangeVehicles 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% 1.4 1.15 -18.06%

Superstreet-US 321 Hickory-Lenoir

2009 – Looking south above Evans Road, PM peak

US 281 (San Antonio TX)

http://www.pape-dawson.com/index.php

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.”

US 281 Superstreet Comments

San Antonio Express-News March 17, 2011

• Preserves the existing facility• Less expensive than an interchange• Provides good access to both sides of the

main road for development

Economically Beneficial

Why Superstreets?

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

• Less time spent idling at a red light• Reduction in environmental pollutants (exhaust fumes / fuel usage)

• Less acreage impacted by construction

and permanent facility

Environmentally Responsible

Why Superstreets?

Superstreet-US 15-501 Chapel Hill

"No Build" 23,998.16            Reduction %

Proposed 21,734.94            2,263.22 9.4%

Superstreet 18,595.24            5,402.93 22.5%

"No Build" 28,597.17            Reduction

Proposed 27,476.82            1,120.35 3.9%

Superstreet 25,468.64            3,128.53 10.9%

"No Build" 251,438.44         Reduction

Proposed 237,039.35         14,399.08 5.7%

Superstreet 209,440.20         41,998.24 16.7%

Estimated Annual Emissions** (kg)

VOC

NO x

CO

SuperstreetsUS 15-501 Chapel Hill

Offset “T” Intersections

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

Alternative Intersection Concepts

Don’t Allow the “Simple” Fourth Leg

• 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

What is a Quadrant Roadway?

NC 73 Quadrant Roadway

2030 Primary Network Delay Analysis (Full Movement vs. Quadrant Left)  AM PM

  Full Movement Quadrant Left % Change 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% 0.20 0.06 -70.58%

Per Veh. Stops 1.85 1.26 -31.48% 2.13 1.58 -25.88%Per Veh. Fuel (gal) 0.06 0.02 -58.83% 0.06 0.03 -49.82%

Capacity Analysis Results2030 Design Year Peak Periods

Jughandles

Main Street – No Lefts

Left In/Out Access

Ingress and Egress Movements at Same Time

Continuous Flow (CFI)

Left Turns Move During Same Phase as Throughs

Continuous Flow (CFI)

Side Street Left Turn at Same Time as Main Left

Continuous Flow (CFI)