union street roundabout turbo-style roundabouts the future?
TRANSCRIPT
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Union Street roundabout
Turbo-style roundabouts – the
future?
Patrick Lingwood
Walking and Cycling Officer
Bedford Borough Council
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Presentation outline• Local importance and problems we faced
• The evolution of the design – Dutch Turbo-roundabout
– What it is and how it works
• Crisis and redesign – Objections
– Redesign principles
• Picture gallery
• Did it work?– Traffic capacity and queuing
– Traffic Speed
– Use of Zebras
• The importance of the design
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Union Street roundabout
Union St Roundabout
Railway Station
Town Centre
Bus Station
A6 traffic Southbound
A6 traffic Northbound Cycling and local traffic to/from station
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Union St Roundabout
Railway station
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2010 Post code plots of children
cycling to Biddenham Upper School
Union St Roundabout
Biddenham Upper School
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Pedestrian and Traffic Flows
Busy multifunctional roundabout - flows per day
(7am -7pm)
– 25,000 motorised vehicles
• 1000 lorries
• 500 buses
• 150 PTWs
– 550 cyclists
• 350 on-road and 200 off-road
– 3000 pedestrians
• 400 children
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Union St roundabout
Names of roads
Clapham Rd
Roff Avenue
Tavistock Street
Union Street
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Union St Roundabout
Railway station
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DfT cyclist safety grant
• 2002 and 2012 36 casualties (8 serious)
• 12 Cyclists: • 8 (1 serious) involved cyclists circulating
• 1 serious a cyclist crossing at the arms
• 24 others• 8 Pedestrians (3 serious) crossing at arms
• 5 PTWs: (1 serious)
• 13 Car drivers/passengers (2 serious)
• The 10 year cost of accidents £1,823,000
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Bicycle flows and accidents
350 on road & 200 off road
Scale 1pt = 10
On-road Off-road
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Evolution of design
DfT Cyclist Safety Bid
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3 Objectives
• Safety:
– Reduce all injury accidents
– especially to cyclists and pedestrians
• Sustainability:
– Encourage walking and cycling
• Traffic:
– no significant impact on capacity or queuing
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Designs evaluated
Options
compared
Injuries Savings £ Savings Traffic
impact
10 years costs KSI Slight KSI Slight KSI Slight £0
1 Do Nothing 8 24 0 0 -1481 -342 -1,823 Base
2 Compact on
road
1 14 7 10 1,296 200 1,438 Yes
3 Compact off-
road
3 15 5 9 926 214 1,140 Yes
4 Circulatory
annular
5 22 3 2 556 28 584 No
5 Spiral annular 2 14 6 10 1,111 200 1,059 Yes
6 Signalised 2 14 6 10 1,111 200 1,311 Yes
7 Turbo-
roundabout
2 14 6 10 1,111 200 1,311 No
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Roff Avenue/Tavistock Street/Clapham Road/Union Street Roundabout
0m 10m 30m
12m central
island radius
44m ICD
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Option submitted to DfT
Raised dividers
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2 lane entries
Zebras and cycle
crossings
2 circulating lanes
where needed
Compact style – entry,
circulating, exit deflection
Raised dividers
Spiral lanes
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Dutch findings:
Capacity and safety
• Capacity
– Higher capacity than single lane compact roundabout
• Safety
– 40-70% safer than alternative junctions and safer than equivalent 2 lane (Dutch) concentric roundabouts
• spiral lanes with fewer conflict points
• slower speeds enforced by geometry
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Crisis and Redesign
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“Raised Dividers” Controversy
• Objections by MAG (Motorcycle Action
Group)
• Meetings with DfT and Sustrans
• Redesign
– Same principles
• speed reduction and spiral roundabout
• “raised dividers” replaced by “virtual dividers”
• opportunity to improve the design
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Raised dividers removed
Build outs on central island
Extended kerbs with
vertical posts
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How the “virtual dividers” work
Straightlining results in tighter
radius of curve at extended kerbs
Following lane results in 3 similar
radii of curve
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Picture Gallery
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Did it work?
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Data collection
• Data was collected at the roundabout at 3 times (7am – 7pm weekdays):
• 2007: (Compact) – when the roundabout was operating as a single lane
compact roundabout because of extended road works on gas mains
• 2012: (Before) – when the roundabout was operating with typical unmarked
wide 2 lane circulating carriageway
• 2014 (After) – when the roundabout had been changed to a turbo-style
roundabout with separated lanes and Zebra crossings on all arms
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All day traffic capacity
0 5000 10000 15000 20000 25000 30000
2014
2012
2007 Car
Lgv
Ogv1
Ogv2
Bus
Mc
Pc
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Peak time capacity
0 500 1000 1500 2000 2500 3000
2014 AM
2012 AM
2007 AM
2014 PM
2012 PM
2007 PM
Car
Lgv
Ogv1
Ogv2
Bus
Mc
Pc
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AM Peak time Queuing (Roff Avenue metres)
0
20
40
60
80
100
120
140
160
07:00 07:10 07:20 07:30 07:40 07:50 08:00 08:10 08:20 08:30 08:40 08:50
2007
2012
2014
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Speed surveys (circulatory carriageway free flow mph)
-5
0
5
10
15
20
25
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
mph
Before
After
Typical cycle speed
4mph
8mph
A
B
6mph
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Benefits of slower speeds
• More comfortable on-road cycling– Small difference between cyclist and vehicle
speed
• Safer (cycling) Zebra crossing– drivers more aware and willing to stop
• Easier to get on roundabout– lower gap acceptance
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Crossing at the Zebras
0
500
1000
1500
2000
2500
2012
Adults
2012
Children
2012
Cyclists
2014
Adults
2014
Children
2014
Cyclists
Zebra/Pelican
Without help
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Conclusion
• So far, it all looks hopeful
• Safety and capacity advantages of
Dutch turbo-roundabouts
• Virtual dividers make it easier to retrofit
• Potential design for other busy urban
roundabouts?
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Source Brilon 2008
Union St Roundabout
Turbo-
style
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Patrick Lingwood
“A scene of smooth tranquillity – it is
so much easier to cross the roads
with the pedestrian crossings and the
sense of intimidation has gone for
car and van drivers, too” – Graeme Hay BMF