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
3 Types of Circular Intersections l Traffic Circle Circular Intersections Columbus Circle – New York City Market Square - Fayetteville
3 Types of Circular Intersections Traffic Circle l Traffic Calming Intersection Circular Intersections
3 Types of Circular Intersections Traffic Circle Traffic Calming Intersection l Modern Roundabout Clemmons, Forsyth Co.NC State, Raleigh Circular Intersections
Roundabout vs. Traffic Circle Size Traffic Circle - ~ 800’ Diameter Roundabout – ~ 180’ Diameter
Roundabout vs. Traffic Circle Deflection Roundabout – 45-60 degree entry Traffic Circle – 90 degree entry
Traffic Circle - Stop Roundabout - Yield Roundabout vs. Traffic Circle Entry 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 Crashes48% Fatal/Injury Crashes in Rural Areas78% 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.orgwww.highwaysafety.org NCHRP Report 572onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_572.pdfonlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_572.pdf NCDOT Safety Evaluation Groupwww.ncdot.org/doh/preconstruct/traffic/safety/Reports/completed.htmlwww.ncdot.org/doh/preconstruct/traffic/safety/Reports/completed.html Roundabouts - Safety Crash 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
l Roundabouts can be designed as ovals and oblong shapes in order to achieve better movement separation and accommodate unique intersection geometry l Works well for offset T-type and multiple legged intersections l Could be an option for median divided facilities where controlling access is an issue Roundabouts – Geometric Flexibility
At a roundabout replacing a signalised junction, CO emissions - 29% NO x emissions - 21% fuel consumption - 28% At a roundabout replacing yield regulated junctions, CO emissions + 4% NO x 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 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) 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
Multi Lane Roundabouts Griffith Street and Davidson Gateway Drive Griffith Street and Jetton 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
Superstreet Benefits and Capacities (Research Project 2009-06) Collision TypeCrash Reduction % Total-46 Fatal and injury-63 Angle and right turns-75 Rear ends 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?
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?
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?
2030 Primary Network Delay Analysis (Full Movement vs. Quadrant Left) AMPM Full MovementQuadrant Left% ChangeFull MovementQuadrant Left% Change Vehicles Exited (veh / hr)6,1277,73626.26%7,4259,08722.38% Vehicles Entered (veh / hr)6,2347,77424.70%7,5579,23122.15% Travel Distance (mi)2,9853,59520.45%3,5124,25621.19% Travel Time (hr)1,128273-75.81%1,566654-58.22% Total Delay (hr)1,044169-83.86%1,464527-63.99% Total Stops11,3109,785-13.48%15,85114,378-9.29% Fuel Useage (gal)358186-48.01%473291-38.59% Per Veh. Distance (mi)0.490.6125.00%0.290.3519.52% Per Veh. Time (hr)0.200.04-82.79%0.210.07-65.86% Per Veh. Delay (hr)0.170.02-87.21%0.200.06-70.58% Per Veh. Stops1.851.26-31.48%2.131.58-25.88% Per Veh. Fuel (gal)0.060.02-58.83%0.060.03-49.82% Capacity Analysis Results 2030 Design Year Peak Periods