Appendix N: Coppid Beech Roundabout Report and Design Options

Appendix N: Coppid Beech Roundabout Report and
Design Options
Project number: 10395845
Dated: 29/07/2013
Revised:
COPPID BEECH ROUNDABOUT – TRAFFIC
ASSESSMENT
Wokingham Borough Council
12/02/2013
Quality Management
Issue/revision
Issue 1
Remarks
Draft for Client
Comment
Date
12 Feb 2013
Prepared by
James Powell
Revision 1
Revision 2
th
Signature
Checked by
Stephen Reed
Signature
Authorised by
Stephen Reed
Signature
Project number
Report number
File reference
Project number:
Dated: 12/02/2013
Revised:
2 | 29
Revision 3
COPPID BEECH ROUNDABOUT – TRAFFIC
ASSESSMENT
12/02/2013
Client
Ian Haller
Major Projects
Wokingham Borough Council
Shute End
Wokingham
Consultant
James Powell
Mountbatten House
Basingstoke
RG21 4HJ
UK
Tel: +44 (0)12 5631 8800
Fax: +44 (0)12 5631 8700
www.wspgroup.co.uk
Registered Address
WSP UK Limited
01383511
WSP House, 70 Chancery Lane, London, WC2A 1AF
WSP Contacts
Stephen Reed 07900152645
3 | 29
Table of Contents
Summary ........................................................................................... 5
Project Background ........................................................................... 6
Assessment ....................................................................................... 8
Flows ................................................................................................. 9
Concept Design ............................................................................... 17
Modelling Results ............................................................................ 20
Conclusions ..................................................................................... 27
Appendices...................................................................................... 28
Project number:
Dated: 12/02/2013
Revised:
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Summary
Coppid Beech Roundabout is a pinch point between Bracknell, Wokingham and Reading. It creates delays of
varying severity for traffic travelling to and from all of these Towns in both the AM and PM peaks. With strategic
developments designated in the local area, traffic utilising the junction is likely to increase significantly.
Modelling was undertaken using the WSTM Wokingham Strategic Traffic Model (WSTM) to forecast traffic
flows in various scenarios for development predictions, these flows are produced in Passenger Car Units
(PCUs). These test scenarios are set out in Chapter XX. The modelling showed that the traffic was forecast to
increase and that the current roundabout will have insufficient capacity to cope with future flows, given that it
already creates traffic delays.
Coppid Beech Roundabout is currently a 4 arm roundabout which is partially signalised on the Southbound sliproad of the A329(M), all other arms – B3408, A329(M) Northbound slip-road and A329 London Road – currently
operate under priority. Traffic signals are also provided on the northern side of the circulatory in advance of the
Southbound slip-road of the A329(M).
A solution was sought that would deliver a route interchange that had minimal delay, with capacity to cope with
future predicted flows. It needed to be within the existing highway boundary and have minimal impact on
existing services and ecology, whilst balancing slip-road and conflicting flows to prevent blocking back onto the
A329(M). As the current layout is a grade separated gyratory the scope of options for change was limited to
increasing lanes under priority control or full signalisation, whilst trying to utilise the existing carriageway layout
as much as possible to keep construction costs to a minimum. As priority junctions can move significantly less
traffic across a stopline than a signalised junction, it was decided that as there is a part signalisation already at
the junction that a fully signalised option would be the most appropriate approach. This would enable the
number of lanes to be kept to less than a priority alternative and give better control of queuing which could
cause blocking onto the A329(M).
It was decided that LinSig would be the best tool to model a fully signalised option. LinSig is a traffic signal
software program that uses signal timings, capacity measurements and flow data to analyse how a junction will
perform. It can be used to iteratively establish how many lanes will be required on a link to handle a given
volume of traffic and balance two opposing links accordingly by optimising the signal timings of each link.
After a review of the turning movements with the modelling team, LinSig models were created for the predicted
flow scenarios. Changes were made for each differing strategic infrastructure scenario for North Wokingham to
alter the number of lanes on the arms and circulatory of Coppid Beech to allow capacity for the forecast traffic
flows. The number of lanes was dictated by the peak of the tidal flows of AM and PM, so where some lanes
may not be required in the AM as the flow is low, these are required in the PM as the flow increases and vice
versa.
The LinSig modelling led to three separate layouts emerging to cope with the different strategic scenarios
tested. All of these layouts were created to provide capacity for the relevant strategic scenario flows, allowing
the junctions to perform well and giving a forward growth allowance of 10-15 years beyond 2026, dependent
upon realised growth rates. These layouts were then drafted into design drawings using AutoCAD.
The modelled scenario FNDR is thought the most likely to occur and the Design Layout 3 option will be taken
forward for full scheme costing. It provides capacity for the predicted growth in the area and also creates some
spare capacity for growth beyond 2026.
5 | 29
Project Background
The following information is provided as an investigation into the current working and potential improvements to
Coppid Beech Roundabout based on predicted outputs from the WSTM for Strategic Development Locations in
and around Wokingham.
The purpose of the work was investigate the capacity of the current layout at Coppid Beech Roundabout and to
conceive junction layout options with increased capacity to cope with predicted future traffic demands for 2026
B3, 2026 C3 and 2026 FNDR (Full Northern Distributor Road) options. The predicted flows for 2026 are based
on the WBC Core Strategy development and infrastructure provisions, extracted from the WSTM transport
model.
As can be seen in Figure 1, Coppid Beech Roundabout is a strategically located interchange between the
A329(M) NB for Reading, the A329 London Road for Wokingham to the West and the A329(M) SB and the
B3408 for Bracknell to the East.
Figure 1: Location Overview
Coppid Beech Roundabout
Project number:
Dated: 12/02/2013
Revised:
6 | 29
Figure 2: Coppid Beech Roundabout Overview
Figure 3: Satellite View of Current Layout
7 | 29
Assessment
A LinSig model was built to replicate the current junction layout. 2008 and 2012 survey flows were input into the
model, the results showed the roundabout to be overcapacity in the current partially signalised layout with one
arm signalised and three arms priority. This highlighted that any increase in flow would likely result in the
requirement for traffic signals and/or more lanes.
The 2026 predicted future year scenarios were examined and compared to the survey flows and showed a
significant increase in traffic on some arms. The decision was taken to examine signalised layouts at the
junction, as this can move more traffic across a stopline than a priority layout, so increasing the available
capacity whilst minimising the number of lanes required.
A FlowRound model was built to gain a perspective on the flow levels and turning movements for the future
year scenarios. This helped to inform choices on the number of lanes and the lane allocation that was required
to cope with the new flows.
Given the high level of traffic on all approaches a partially (three arm) signalised junction was not an option. A
fully signalised layout model was constructed in LinSig, the predicted future flows were again used to aid the
design for the number of lanes through the gyratory, the number of lanes on the approaches and the flare
lengths required to enable the junction to perform within guideline tolerances (85% Degree of Saturation). The
smallest permissible number of lanes was used, whilst maintaining the capacity on all approaches and
circulatory lanes.
Each scenario was subject to the same process of model optimisation and minimisation, before the final layout
was taken through to design drafting.
Project number:
Dated: 12/02/2013
Revised:
8 | 29
Flows
All flows are shown in PCUs (passenger car units).
9 | 29
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Dated: 12/02/2013
Revised:
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11 | 29
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Dated: 12/02/2013
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Project number:
Dated: 12/02/2013
Revised:
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15 | 29
Flow Comparison
The comparison between the survey 2012 traffic flows and the respective 2026 predicted scenario flows are
shown in table 1, all flows are in PCUs.
Table 1 – Flow Comparions 2012 – 2026 B3, C3, FNRR, C, C-2A and C-9A:
Project number:
Dated: 12/02/2013
Revised:
16 | 29
Concept Design
A concept design, based on OS backgrounds, was progressed for the optimal design layout identified for option
B3, C3 and FNRR (Full Northern Relief Road). All designs incorporate pedestrian and cyclist crossing facilities.
The concept design drawings GA/001, GA/002 and GA/003 can be found in APPENDIX I. Below are snapshots
of the layouts.
Design Layout (1):
Design Layout (1) is the option with the fewest changes to the current layout. It provides a minimum of 3 lanes
on the Southern and Western circulatory. Increases to the SB A329(M) off-slip to include a 3 lane flare and an
increase on the B3408 approach to include a 4 lane flare.
17 | 29
Design Layout (2):
Design Layout (2) provides a minimum of 4 lanes on the southern circulatory and 3 lanes on the Western circulatory. Increases to the SB A329(M) off-slip to include a 3 lane flare and an increase on the B3408 approach
to include a 4 lane flare. The Eastern approach from the A329 London Road also has a 4 lane flare.
Project number:
Dated: 12/02/2013
Revised:
18 | 29
Design Layout (3):
Design Layout (3) provides for a minimum of 4 lanes on the southern circulatory and 3 lanes on the Western
and Eastern circulatory. The Northern circulatory has 3 lanes. Increases to the SB A329(M) off-slip to include a
3 lane flare and an increase on the B3408 approach to include a 3 lane flare. The Eastern approach from the
A329 London Road has a 4 lane flare.
19 | 29
Modelling Results
Following the modelling design approach outlined previously, concept design drawings were completed for B3,
C3 and FNDR.
As can be seen from the results in Tables 3 to 8, all lanes remain within (or very close to) guideline DoS of
85%. All models were optimised to increase the approach lanes to close to or slightly over capacity to maintain
the smallest internal queue possible.
Whereas LinSig will optimise the cycle times and use the internal capacity to its maximum to decrease delay on
all lanes equally; the reduced internal queuing model is more representative to how the junction would operate
in reality.
All layouts perform well in the 2026 scenario that they have been optimised and designed for. Table 2 shows
the design layout used for the modelling and the PRC values for all scenarios in AM and PM.
Table 2 – PRC Values for Scenarios:
SCENARIO
B3
C3
FNRR
C
C – Option 2A
C – Option 9A
Project number:
Dated: 12/02/2013
Revised:
AM PRC(%)
4.6
3.6
6.7
6.6
3.7
1.8
PM PRC(%)
3.7
2.7
3.2
7.1
4.2
4.3
20 | 29
Design Layout
(1)
(2)
(3)
(2)
(3)
(2)
Table 3 – Scenario B3 Modelling Results:
Scenario B3
AM
PM
Lane Description
Deg Sat (%)
Mean Max
Queue (pcu)
Deg Sat (%)
Mean Max
Queue (pcu)
A329(M) SB Ahead Ahead2
85.5%
12.9
80.0%
11.9
A329(M) SB Ahead
59.8%
7.1
85.2%
13.5
B3408 WB Left Ahead
60.2%
6.9
69.0%
9.6
B3408 WB Ahead
86.1%
13.8
85.8%
17.4
A329(M) NB Ahead Ahead2
86.0%
13.7
85.2%
10.1
A329(M) NB Ahead
19.0%
2.0
44.4%
3.9
A329 London Road EB Left Ahead
84.7%
14.3
68.1%
8.3
A329 London Road EB Ahead
82.4%
13.3
86.8%
12.8
Gyratory EB Ahead
63.6%
6.2
54.5%
8.2
Gyratory EB Ahead Right
63.7%
6.1
58.2%
9.2
Gyratory SB Ahead
35.1%
3.6
51.0%
7.7
Gyratory SB Ahead Right
33.5%
5.6
59.2%
7.7
Gyratory WB Right
52.4%
6.8
41.8%
5.9
Gyratory WB Right Right2
51.0%
7.4
67.5%
9.6
Gyratory WB Right
46.0%
6.9
55.9%
8.0
Gyratory NB Ahead
64.2%
6.6
81.2%
8.5
Gyratory NB Ahead
69.5%
7.6
85.3%
9.8
Gyratory NB Right
16.1%
1.3
21.8%
4.2
PRC Over All Lanes
4.6%
3.7%
21 | 29
Table 4 – Scenario C3 Modelling Results:
Scenario C3
AM
PM
Lane Description
Deg Sat (%)
Mean Max
Queue (pcu)
Deg Sat (%)
Mean Max
Queue (pcu)
A329(M) SB Left Ahead
86.9%
12.2
85.0%
15.1
A329(M) SB Ahead
59.5%
6.3
60.7%
9.8
B3408 WB Left Ahead
61.8%
6.1
86.8%
17.0
B3408 WB Ahead
86.4%
11.7
86.7%
18.3
A329(M) NB Ahead Ahead2
85.8%
13.2
87.6%
11.9
A329(M) NB Ahead
2.2%
0.2
26.8%
2.4
A329 London Road EB Left
54.3%
6.6
50.9%
5.1
A329 London Road EB Ahead
83.8%
13.6
85.0%
12.4
Gyratory EB Ahead
71.5%
6.8
60.9%
5.2
Gyratory EB Ahead Right
71.8%
6.3
67.8%
5.5
Gyratory SB Ahead Right
37.2%
1.6
78.7%
17.6
Gyratory SB Right
29.1%
6.7
56.2%
11.5
Gyratory WB Right
37.2%
3.0
49.6%
9.7
Gyratory WB Right
33.2%
6.7
54.4%
13.3
Gyratory WB Right
46.5%
4.6
51.7%
8.0
Gyratory WB Right
45.8%
4.6
56.1%
8.8
Gyratory NB Ahead
82.4%
6.8
68.3%
7.7
Gyratory NB Ahead Right
83.1%
6.9
75.9%
9.8
Gyratory NB Right
2.7%
0.3
12.6%
0.8
PRC Over All Lanes
Project number:
Dated: 12/02/2013
Revised:
3.6%
2.7%
22 | 29
Table 5 – Scenario FNDR Modelling Results:
Scenario FNRR
AM
PM
Lane Description
Deg Sat (%)
Mean Max
Queue (pcu)
Deg Sat (%)
Mean Max
Queue (pcu)
A329(M) SB Left
67.8%
5.9
82.1%
9.4
A329(M) SB Left Ahead
67.6%
5.9
82.1%
9.4
A329(M) SB Ahead
81.4%
8.3
84.0%
10.1
B3408 WB Left Ahead
51.7%
3.8
87.2%
11.4
B3408 WB Ahead
70.3%
6.0
80.7%
9.3
B3408 WB Ahead
70.1%
6.0
80.6%
9.3
A329(M) NB Left
36.9%
3.1
52.4%
3.9
A329(M) NB Left Ahead
36.8%
3.0
52.3%
3.9
A329 London Road EB Left
82.4%
10.9
70.7%
6.0
A329 London Road EB Left Ahead
82.6%
11.0
70.7%
6.0
A329 London Road EB Ahead
82.1%
10.9
69.1%
5.9
A329 London Road EB Ahead
66.2%
7.1
65.8%
5.5
Gyratory EB Ahead
54.6%
0.6
52.8%
4.4
Gyratory EB Ahead Right
81.0%
2.7
49.9%
5.4
Gyratory EB Right
65.4%
2.2
47.5%
5.1
Gyratory SB Ahead
18.4%
2.0
36.2%
4.0
Gyratory SB Ahead Right
60.3%
6.2
77.6%
8.3
Gyratory SB Right
50.4%
0.0
75.8%
0.0
Gyratory WB Ahead
46.4%
3.3
83.7%
8.0
Gyratory WB Ahead
84.4%
7.1
63.8%
8.4
Gyratory WB Right
66.6%
5.1
64.2%
0.0
Gyratory WB Right
66.4%
5.0
64.1%
0.0
Gyratory NB Ahead
62.7%
0.0
61.7%
0.0
Gyratory NB Ahead
62.5%
0.0
61.6%
0.0
Gyratory NB Right
1.1%
0.1
8.8%
1.2
PRC Over All Lanes
6.7%
3.2%
23 | 29
Table 6 – Scenario C Modelling Results:
Scenario C
AM
PM
Lane Description
Deg Sat (%)
Mean Max Queue
(pcu)
Deg Sat (%)
Mean Max Queue
(pcu)
A329(M) SB Left Ahead
82.1%
9.7
82.5%
11.7
A329(M) SB Ahead
68.8%
7.0
72.7%
9.1
B3408 WB Left Ahead
56.4%
4.6
72.0%
7.0
B3408 WB Ahead
84.5%
9.6
84.0%
11.9
A329(M) NB Ahead Ahead2
81.9%
10.3
76.4%
6.6
A329(M) NB Ahead
5.0%
0.4
22.2%
1.4
A329 London Road EB Left
67.1%
7.6
56.6%
4.3
A329 London Road EB Ahead
83.1%
11.6
83.7%
8.4
Gyratory EB Ahead
71.0%
7.8
54.9%
6.8
Gyratory EB Ahead Right
72.4%
6.9
66.5%
7.7
Gyratory SB Ahead Right
31.9%
2.5
59.4%
6.7
Gyratory SB Right
34.4%
6.5
55.4%
5.0
Gyratory WB Right
26.0%
0.3
44.3%
6.4
Gyratory WB Right
38.9%
7.1
60.6%
5.9
Gyratory WB Right
42.7%
5.3
48.7%
10.6
Gyratory WB Right
41.8%
4.3
47.9%
10.7
Gyratory NB Ahead
79.2%
2.6
74.8%
5.4
Gyratory NB Ahead Right
79.4%
3.5
75.8%
5.5
Gyratory NB Right
5.9%
0.6
11.3%
1.3
PRC Over All Lanes
Project number:
Dated: 12/02/2013
Revised:
6.6%
7.1%
24 | 29
Table 7 – Scenario C Option 2A Modelling Results:
Scenario C Option 2A
AM
PM
Lane Description
Deg Sat (%)
Mean Max Queue
(pcu)
Deg Sat (%)
Mean Max Queue
(pcu)
A329(M) SB Left Ahead
84.7%
12.3
83.2%
13.0
A329(M) SB Ahead
69.9%
8.6
72.1%
9.8
B3408 WB Left Ahead
66.3%
6.7
72.4%
7.6
B3408 WB Ahead
84.2%
10.9
82.2%
13.0
A329(M) NB Ahead
86.3%
9.6
85.5%
8.0
A329(M) NB Ahead Ahead2
86.5%
9.7
85.9%
8.2
A329 London Road EB Left Ahead
86.8%
18.0
86.4%
10.5
A329 London Road EB Ahead
79.3%
14.6
84.2%
11.0
Gyratory EB Ahead
47.0%
5.4
54.6%
8.0
Gyratory EB Ahead Right
70.0%
7.9
63.3%
9.5
Gyratory EB Right
64.4%
6.5
42.8%
6.2
Gyratory SB Ahead
10.3%
0.8
34.1%
6.6
Gyratory SB Ahead Right
58.2%
6.9
62.5%
7.0
Gyratory SB Right
31.0%
8.6
55.0%
6.0
Gyratory WB Right
29.3%
8.8
42.7%
1.3
Gyratory WB Right
28.6%
0.8
60.3%
1.9
Gyratory WB Right
30.4%
9.0
46.9%
7.9
Gyratory WB Right
29.5%
8.9
42.7%
7.2
Gyratory NB Ahead
73.5%
3.9
74.8%
5.4
Gyratory NB Ahead Right
74.2%
4.1
79.8%
6.6
PRC Over All Lanes
3.7%
4.2%
25 | 29
Table 8 – Scenario C Option 9A Modelling Results (LAR):
Scenario C Option 9A
AM
PM
Lane Description
Deg Sat (%)
Mean Max Queue
(pcu)
Deg Sat (%)
Mean Max Queue
(pcu)
A329(M) SB Left Ahead
85.8%
11.8
85.6%
15.1
A329(M) SB Ahead
56.0%
5.8
72.0%
11.3
B3408 WB Left Ahead
44.0%
3.2
72.4%
8.7
B3408 WB Ahead
81.0%
9.9
86.0%
15.4
A329(M) NB Ahead Ahead2
79.7%
11.2
86.3%
12.2
A329(M) NB Ahead
5.4%
0.5
20.0%
1.9
A329 London Road EB Left
49.0%
5.8
46.6%
4.8
A329 London Road EB Ahead
88.4%
15.8
85.3%
13.1
Gyratory EB Ahead
75.6%
7.1
56.7%
5.1
Gyratory EB Ahead Right
77.8%
7.8
63.5%
5.8
Gyratory SB Ahead Right
50.8%
2.7
70.2%
9.9
Gyratory SB Right
27.4%
6.3
50.5%
7.6
Gyratory WB Right
26.1%
2.4
42.0%
4.6
Gyratory WB Right
44.0%
6.9
62.3%
9.6
Gyratory WB Right
43.7%
4.0
50.4%
11.4
Gyratory WB Right
42.9%
4.0
48.7%
10.5
Gyratory NB Ahead
77.3%
5.3
67.1%
6.7
Gyratory NB Ahead Right
77.8%
5.4
73.4%
8.2
Gyratory NB Right
6.6%
0.7
4.6%
0.9
PRC Over All Lanes
Project number:
Dated: 12/02/2013
Revised:
1.8%
4.3%
26 | 29
Conclusions
After detailed modelling of current and future scenarios, suitable designs were completed for the junctions that
would cope with 2026 future year predicted traffic growth for their respective scenarios.
The completed modelling shows that the junctions all perform within or very close to the guideline 85% Degree
of Saturation (DoS) for all lanes. The models have been optimised to allow for minimal internal queuing whilst
keeping the approach lanes utilised. The practical reserve capacity (PRC) in all of the designed junctions is
suitable for the predicted growth and allows for a 10 – 15 year design life of the junctions, dependent upon realised growth rates.
The modelled scenario FNDR is the most likely to occur and as such the Design Layout 3 option will be taken
forward for costing. It provides capacity for the predicted growth in the area and also creates spare capacity for
growth beyond 2026.
27 | 29
Appendices
APPENDIX A
Layout 1: GA/001
Layout 2: GA/002
Layout 3: GA/003
Project number:
Dated: 12/02/2013
Revised:
28 | 29
c WSP Group Ltd
Key:Road
Shared Cycleway/Footway
Grassed areas
c WSP Group Ltd
Key:Road
Shared Cycleway/Footway
Grassed areas
c WSP Group Ltd
WSP UK Limited
Mountbatten House
Basingstoke
RG21 4HJ
UK
Tel: +44 (0)12 5631 8800
Fax: +44 (0)12 5631 8700
www.wspgroup.co.uk