Union Street roundabout Turbo-style roundabouts the future?

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

Patrick.lingwood@bedford.gov.uk

“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