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
A6 traffic Southbound
A6 traffic Northbound
Cycling and local traffic to/from station
Union St Roundabout
Town Centre
Railway Station
Bus 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
Clapham Rd
Roff Avenue
Tavistock Street
Union St roundabout
Names of roads
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
10 years costs
Injuries
Savings
£ Savings
Traffic
impact
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 offroad
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 Turboroundabout
2
14
6
10
1,111
200
1,311
No
12m central
island radius
44m ICD
0m
10m
30m
Roff Avenue/Tavistock Street/Clapham Road/Union Street Roundabout
Option submitted to DfT
Raised dividers
2 lane entries
2 circulating lanes
where needed
Raised dividers
Spiral lanes
Zebras and cycle
crossings
Compact style – entry,
circulating, exit deflection
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
Extended kerbs with
vertical posts
Build outs on central island
How the “virtual dividers” work
Following lane results in 3 similar
radii of curve
Straightlining results in tighter
radius of curve at extended kerbs
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
2007
Car
Lgv
Ogv1
Ogv2
Bus
Mc
Pc
2012
2014
0
5000
10000
15000
20000
25000
30000
Peak time capacity
2007 PM
2012 PM
Car
Lgv
Ogv1
Ogv2
Bus
Mc
Pc
2014 PM
2007 AM
2012 AM
2014 AM
0
500
1000
1500
2000
2500
3000
AM Peak time Queuing
(Roff Avenue metres)
160
140
2007
2012
2014
120
100
80
60
40
20
0
07:00
07:10
07:20
07:30
07:40
07:50
08:00
08:10
08:20
08:30
08:40
08:50
Speed surveys
(circulatory carriageway free flow mph)
25
4mph
Before
After
20
A
8mph
15
B
10
5
6mph
0
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
-5
mph
Typical cycle speed
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
2500
2000
Zebra/Pelican
Without help
1500
1000
500
0
2012
2012
2012
Adults Children Cyclists
2014
2014
2014
Adults Children Cyclists
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?
Union St Roundabout
Turbostyle
Source Brilon 2008
“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
Patrick Lingwood
Patrick.lingwood@bedford.gov.uk