Revolutionise roundabout design

Revolutionise Roundabout Design for Local Road NetworkCycling Friendly Infrastructure on Bike Boulevard2015 AITPM National Conference

Bill Zhang, Tonkin ConsultingZhimin Ma, Department of Planning, Transport & Infrastructure, South Australia

An Overview• Background•Objectives•Methodology• Problem Identification• Literature Review•Design Philosophies•Concept Development•Challenges•Recommendations

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Background• Boom in cyclist volumes

in recent years as South Australians are now increasingly making the decision to adopt the sustainable, healthier and cheaper alternative for their every day commute

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Background• Key challenges for road authorities

to construct, retrofit and maintain infrastructure to accommodate to ensure the safe and efficient travel for cyclists and other road users• High percentages of injury crashes

involving cyclists at roundabouts within local road network

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Objectives• Investigate cost effective

options to promote cyclists safety at existing local area roundabout intersections• Adopting the safe systems

approach to road safety Towards Zero Together - Safer Roads

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Methodology

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The Problem• In South Australia,

41% of overall Cyclist Injury Crashes at intersections are occurred at roundabouts between 2008 - 2012

• 43% of all injury crashes at local roundabouts involved cyclists

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Literature ReviewKey Findings• Vehicle Entry Speeds is A

KEY FACTOR

• Cyclist Lateral Tracking to the left

• Bike Lanes inside Roundabouts are Ineffective

Austroads Research Report, May 2014• Assessment of the effectiveness

of On-road Bicycle Lanes at Roundabouts in Australia and NZ

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Design Philosophies• Entry Speeds - Reduce to below 30km/h• Horizontal Geometry Design • Radial (Continental European) vs • Tangential

• Vertical Geometric Treatment • Raised Platforms, • Speed humps prior to entry curve

• Reduce Cyclist Lateral Tracking to the left• Encourage Cyclists to command lane• Increase Cyclist visibility (to be seen)

Radial Tangential

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Concept Development• Tighter entry curvature and design

envelop of the radial approach makes it possible to obtain equitable speeds between all users

• Cyclists should be encouraged to claim the entry and circulating lane to eliminate the risk of side swipes and makes themselves more noticeable to drivers

• Concepts to create an slower operating environment around the target location

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Site Selection & Analysis – Beulah Rd / Sydenham Rd

• Beulah Rd – Popular Commuting Cyclist Route

• 10 Cyclist Injury Crashes in the last 5 years – 62.5% cyclist crashes

• All Injury crashes are Right Angle• Cars at fault 100% of time

(reported)• Speeds – 85th percentile = 35km/h

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Option 1 – Radial Entries

• Increase entry curvature• Reduce design envelope• Modification to splitter and

kerbside protuberances• Reduce entry widths• Preferable to use semi-

mountable central island

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Option 2 – Radial Entries + Oval Central Island

• Kerbside protuberances and splitter islands are as Option 1• Central island elongated East to

West to slow vehicles approaching from North & South

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Square-about Reverse CurveOther Options Investigated

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Exit ProtuberancesPerceptual Countermeasures

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Central Parking/Landscaping Turbo Roundabout

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Challenges

• Testing the new roundabout concept – evaluation of safety benefits• Community acceptance – potential impact on existing on-street

parking, access to driveways• Integration with surrounding infrastructure and amenity• Cyclist merging with other traffic at approaches• Constructability – no full road closure during construction• Construction and maintenance cost

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Recommendations

• Safety outcome• Cost effective solution• Reduce Entry Speeds• Reduce Cyclist Lateral Tracking• Limited Construction Footprint and

Time

Option 1 - Radial Entry Design will provide the following benefits:

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Future Steps• Stakeholders and local councils

are supportive of the innovative roundabout concept

• A trial of the radial roundabout concept on Norwood-Magill Bicycle Boulevard, involves modification of four existing local street roundabouts

• Construction works commenced in May 2015 and completed by the end of June 2015

• Post-construction evaluations, including a 6-month & a 12-month after completion of construction, will be undertaken to assess impact on road safety, operational performance and driver behaviour at the trial sites

Trials of Radial Roundabout Design on Bike Boulevard

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Modification of Tangential Roundabout to Radial

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Modification of Tangential Roundabout to Radial

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Modification of Traffic Islands

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Thank you

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