modern roundabouts: safety & mobility wrapped in a pretty package
DESCRIPTION
http://www.ohm-advisors.com - Mad about Modern Roundabouts: Coupling Safety and Mobility. This presentation delivers a primer on roundabouts, the differences between roundabouts, traffic circles and rotaries, and the important rules of roundabouts.TRANSCRIPT
Jim Marcinkowski, PE
ASCE, APWA & SWE
Redding, California
May 17, 2010
Short History of Driving in Circles Some Roundabout Basics Safety Users (How To)
Pedestrians Bicycles Drivers
Mobility (Congestion) Before/After Comparisons Aesthetics
No Controls
Take Your Turn
Follow Rules of Road
Right of Way Rule (Yield to Right)
STOP Signs
Police Control
Traffic Signals
Special Turn Lanes & Signals
Vehicle & Pedestrian Detection
Coordinated Signal Systems
Shape Controls
MovementView of Columbus circle, Circa 1915 (Courtesy: New York Department of Planning)
Circles, Small and Large Really Big, High Speed Circles Are Called Rotaries
Yield-To-Right
Circulating traffic yield to the entering vehicles.
Meanwhile in England…
Yield-To-Left
Entering vehicles yield to the circulating traffic.
Roads Are The Most Dangerous
Public Facilities
On The Face Of The Earth
In the U.S., about 800 people are killed each week.
TRAFFIC SIGNALSARE NOT SAFETY DEVICES
32 Vehicle/Vehicle
24 Vehicle/Pedestrian
8 Vehicle / Vehicle
8 Vehicle / Pedestrian
Allcrashes
All injury crashes
Serious injury & fatal crashes
Week by Week reporting of accidents (Feb, 2008)
- no accidents reported since 12/12/07 (source: West Bloomfield Township)
NO INJURY ACCIDENTS
Minor Damage Majority of Citations
Failure to Yield Unsafe Lane Change
(17+ seconds curb to curb) (<4 seconds each crossing)
Typical Intersection = 60’ vs.Roundabout = 13’ x 2
Goals of Roundabouts: Yield on entry Slow, consistent speeds entering/ thru/ exiting
Size as small as practical Path deflection on entry
Limits the number of vehicle to vehicle & vehicle to pedestrian conflicts
Narrated by
Paul W. Smith
Expression of both: Capacity Driver perception
Ranges from ‘A’ (best) to ‘F’ (worst)
Primarily based on measure of average delay
Best demonstrated through a review of a case study:
US-23/THOMPSON ROAD
Tight Diamond Rural interchange Thompson Road – 2 lanes
2 lane bridge over US-23
US-23 – 4 lanes On/off ramps – Single lane w/stop control
Rural Interchange w/ Improvements
Widen Thompson Road to five lanes including bridge Widen ramps for right and left turn lanes Install traffic signals Construction cost = $7 m Need additional land
NOT SELECTED…
Roundabouts at Ramps
Do Not Widen Thompson Rd Do Not Widen Ramps Install Single-lane Roundabout at each ramp termini Construction Cost = $ 2.5 M No additional land needed
2003
C F C A24.1 1934.4 31.8 3.3
1934.4 seconds = 32 + minutes
No Change
Add
Turning
Lanes &
Signal
Single Lane Roundabout
Thompson Rd at US-23 NB Off-Ramp p.m. Period
Level Of Service (LOS)Average Delay (Sec./ Veh.)
2025
One-Way STOP
2003
C F C A24.1 1934.4 31.8 3.3
Thompson Rd at US-23 NB Off-Ramp p.m. Period
2025
One-Way STOP
Level Of Service (LOS)
No Change
Add
Turning
Lanes &
Signal
Single Lane Roundabout
Average Delay (Sec./ Veh.)
2003
C F C A24.1 1934.4 31.8 3.3
Thompson Rd at US-23 NB Off-Ramp p.m. Period
2025
Level Of Service (LOS)Average Delay (Sec./ Veh.)
One-Way STOP
No Change
Add
Turning
Lanes &
Signal
Single Lane Roundabout
Roundabouts At Ramps
Selected as the recommended alternative Best LOS Lowest delay Lowest cost
Half mile strip commercial area. 20,000 ADT
No access management = numerous turning conflicts
Existing pavement width = 80’ - “sea of pavement”
Two traffic signals w/third needed
New shopping center was being proposed.
Reduce speed through the section Improve safety Improve access for businesses and
residential neighborhoods Create pedestrian friendly
environment Improve aesthetics
Reduce speed through the section Reduction of 85th percentile speed from 48 mph
to 33 mph Reduction in average delay time, i.e., it takes
less time to drive this segment of road even with a 15 mph reduction in speed
Improve safety Crash rate reduced 88% even with
increased traffic flows from new development
Reduced severity of accidents Reduce # of injuries.
Before rate = 10/year
After rate = 1/5 years
Improve access for businesses and residential neighborhoods
Over first five years after construction - 60% growth in sales tax revenue for this corridor. Nearly flat sales tax revenue growth for the rest of Golden, CO over same time period
Elimination of large traffic queues from parking lots
Create pedestrian friendly environment
Improve aesthetics
Defined roundabout Use / location Benefits
Safety Traffic calming Capacity Environmental
Emissions - Stormwater Aesthetics
Reduces the number & severity of crashes. Reduces the number of conflict points. Increases capacity, usually w/ fewer approach lanes. Minimizes ROW needed. Can be closely spaced (to structures, traffic signals or
other Rdbts). Adapts to unusual geometry.
May not be suitable for locations: Imbalanced traffic flows, Poor stopping sight distance, Steep grades (>5%) w/ heavy truck traffic, Close to railroad crossings, Within system of coordinated traffic signals.
Existing congestion problems Known safety problems Balanced entering traffic volumes, or High percentage turning movements
Roundabouts: An Information Guide, FHWA 2000 NCHRP 3-78 IMPROVING ACCESS TO ROUNDABOUTS AND
CHANNELIZED TURN LANES FOR THE VISUALLY IMPAIRED
www.roundaboutsusa.com www.ksu.edu/roundabouts/ www.alaskaroundabouts.com www.roundabout.kittelson.com West Bloomfield Township RCOC Dan Hartman – [email protected] Northeast Roundabouts
A Coupling of Safety and Mobility
QUESTIONS?
Initial Costs To Build Surface area paved Staging construction Traffic signs Pavement markings Traffic & pedestrian signals Street lighting
Annual Costs To Operate Electrical & Communication Relamping Depreciating equipment Pavement markings Crash damage to equipment Emergency service providers
responses to crashes
8 Roundabouts in West Bloomfield Township / Farmington Hills – Joint MDOT, RCOC, City & Twp.
