union street roundabout turbo-style roundabouts the future?
TRANSCRIPT
Union Street roundabout
Turbo-style roundabouts – the
future?
Patrick Lingwood
Walking and Cycling Officer
Bedford Borough Council
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
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
Union St Roundabout
Railway station
2010 Post code plots of children
cycling to Biddenham Upper School
Union St Roundabout
Biddenham Upper School
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
Union St roundabout
Names of roads
Clapham Rd
Roff Avenue
Tavistock Street
Union Street
Union St Roundabout
Railway station
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
Bicycle flows and accidents
350 on road & 200 off road
Scale 1pt = 10
On-road Off-road
Evolution of design
DfT Cyclist Safety Bid
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
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
Roff Avenue/Tavistock Street/Clapham Road/Union Street Roundabout
0m 10m 30m
12m central
island radius
44m ICD
Option submitted to DfT
Raised dividers
2 lane entries
Zebras and cycle
crossings
2 circulating lanes
where needed
Compact style – entry,
circulating, exit deflection
Raised dividers
Spiral lanes
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
Crisis and Redesign
“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
Raised dividers removed
Build outs on central island
Extended kerbs with
vertical posts
How the “virtual dividers” work
Straightlining results in tighter
radius of curve at extended kerbs
Following lane results in 3 similar
radii of curve
Picture Gallery
Did it work?
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
All day traffic capacity
0 5000 10000 15000 20000 25000 30000
2014
2012
2007 Car
Lgv
Ogv1
Ogv2
Bus
Mc
Pc
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
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
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
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
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
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?
Source Brilon 2008
Union St Roundabout
Turbo-
style
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