Transport Plan for Thetford - Highway Interventions February 2011 Norfolk County Council
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Transport Plan for Thetford
Highway Interventions
February 2011
Norfolk County CouncilTransport Plan for
233902 BSE NOR 5-1 C
Thetford
C:\DOCUME~1\jol05796\OTLocal\PIMSLI~1\Workbin\57A697FC.R.O\Hig
hway Interventions Rep 5-1C.doc
21 February 2011
Highway Interventions
February 2011
Norfolk County Council
County Hall, Martineau Lane, Norwich, Norfolk NR1 2SG
Mott MacDonald, 7th Floor, County Hall, Martineau Lane, Norwich NR1 2US, United Kingdom
T +44(0) 1603 767 530 F +44(0) 1603 226 760, W www.mottmac.comTransport Plan for Thetford
Highway Interventions
Issue and revision record
Revision Date Originator Checker Approver Description
A March 2010 A Smith CN Jolley CR Aston First Draft for Initial Comments
Revised draft with changed
B November 2010 A Smith CN Jolley GA Kelly
parameters
C February 2011 G Smith CN Jolley GA Kelly Final. Intervention costing and
drawings added. Additional
clarifications.
This document is issued for the party which commissioned it We accept no responsibility for the consequences of this
and for specific purposes connected with the above-captioned document being relied upon by any other party, or being used
project only. It should not be relied upon by any other party or for any other purpose, or containing any error or omission
used for any other purpose. which is due to an error or omission in data supplied to us by
other parties
This document contains confidential information and proprietary
intellectual property. It should not be shown to other parties
without consent from us and from the party which
commissioned it.
Mott MacDonald, 7th Floor, County Hall, Martineau Lane, Norwich NR1 2US, United Kingdom
T +44(0) 1603 767 530 F +44(0) 1603 226 760, W www.mottmac.comTransport Plan for Thetford Highway Interventions Content Chapter Title Page Executive Summary i 1. Introduction 1 1.1 Purpose of this Report _______________________________________________________________ 1 1.2 Report Structure ____________________________________________________________________ 1 2. Baseline Traffic Data 2 2.1 Introduction________________________________________________________________________ 2 2.2 Traffic Surveys _____________________________________________________________________ 2 2.2.1 Automatic Number Plate Recognition Surveys (ANPR) and Manual Classified Counts (MCC) ________ 2 2.2.2 Cordon Automatic Traffic Counts (ATC) __________________________________________________ 3 2.2.3 Road Side Interview Surveys (RSI) _____________________________________________________ 3 2.3 Peak Hours________________________________________________________________________ 3 3. Base Scenario 4 3.1 Introduction________________________________________________________________________ 4 3.2 Assessment Methodology ____________________________________________________________ 4 4. TEMPRO Growth Factor 7 4.1 Trip Growth Assumptions _____________________________________________________________ 7 5. Link Capacities 11 5.1 Introduction_______________________________________________________________________ 11 5.2 Assumed Link End Capacities for Thetford ______________________________________________ 11 6. Do-Minimum Scenario 12 6.1 Introduction_______________________________________________________________________ 12 6.2 Trip Rate Calculations ______________________________________________________________ 12 6.2.1 Residential Trip Rates ______________________________________________________________ 12 6.2.2 Employment Trips – Mode Share ______________________________________________________ 14 6.3 SUE Residential Generated Traffic ____________________________________________________ 14 6.3.1 Traffic Flows ______________________________________________________________________ 14 6.3.2 Distribution on the Network __________________________________________________________ 15 6.3.3 Non-Journey to Work Vehicle Trips ____________________________________________________ 16 6.4 TAAP Employment Generated Traffic __________________________________________________ 17 6.4.1 Distribution on the Network __________________________________________________________ 20 6.5 2026 Traffic Distribution _____________________________________________________________ 23 6.5.1 HGV Traffic Growth Assumptions______________________________________________________ 24 7. Do-Something Scenario 27 7.1 Introduction_______________________________________________________________________ 27 7.2 Reduced Containment within the SUE and Soft Measures __________________________________ 27 7.3 Link Capacity _____________________________________________________________________ 30 7.3.1 Development without Soft Measures ___________________________________________________ 30 233902/BSE/NOR/5-1/C 21 February 2011
Transport Plan for Thetford Highway Interventions 7.3.2 Development with Soft Measures ______________________________________________________ 31 7.4 Physical Measures _________________________________________________________________ 31 7.4.1 Internal Junctions __________________________________________________________________ 31 7.4.2 Internal Links _____________________________________________________________________ 31 7.4.3 A11 Junctions_____________________________________________________________________ 32 7.5 Assessment Scenarios ______________________________________________________________ 32 8. A11 Junction Assessments 33 8.1.1 Roundabout – A11 with London Road __________________________________________________ 33 8.1.2 Roundabout – A11 with A134 Brandon Road_____________________________________________ 34 8.1.3 Roundabout – A11 with Mundford Road_________________________________________________ 36 8.1.4 Slip Roads – A11 with Croxton Road ___________________________________________________ 37 8.1.5 Roundabout – A11 with Norwich Road__________________________________________________ 39 8.2 Summary of A11 Junction Assessment Work_____________________________________________ 40 9. Internal Junction Assessments 42 9.1.1 Priority Junction – Mundford Road with Croxton Road______________________________________ 42 9.1.2 Signalised Junction – Brandon Road, Bury Road and London Road ___________________________ 43 9.1.3 Roundabout – Norwich Road, Mundford Road and Hurth Way _______________________________ 44 9.1.4 Roundabout – Hurth Way, A1066, A1088 Thetford Road and Castle Street _____________________ 45 9.2 Summary of Internal Junction Assessments______________________________________________ 46 10. Intervention Costing 47 11. Summary and Conclusions 48 11.1 Summary ________________________________________________________________________ 48 11.2 Conclusion _______________________________________________________________________ 49 Appendices 50 Appendix A. Plan showing Traffic Survey Sites _____________________________________________________ 51 Appendix B. Indicative Plans of Junction Mitigation Interventions _______________________________________ 53 Appendix C. Summary of Junction Assessment values _______________________________________________ 65 Appendix D. Trip Generation Summary ___________________________________________________________ 67 D.1. Thetford SUE Residential Vehicle Trip Generation ________________________________________ 68 D.2. Thetford Area Action Plan (TAAP) Employment Sites Vehicle Trip Generation ___________________ 69 D.3. Total SUE and TAAP traffic that would be removed from A11 after applications of Smarter Choices __ 69 Tables Table 4.1: TEMPRO Growth Factors_____________________________________________________________ 7 Table 4.2: Regional Spatial Strategy Data ________________________________________________________ 7 Table 4.3: TEMPRO Growth Factors for Car Drivers (Average Weekday – Thetford) 2009 - 2021______________ 7 Table 4.4: Average Weekday Trips by Car Drivers (future year minus base year) __________________________ 8 Table 5.1: Hourly One-way Link End Capacities for Thetford Urban Trunk Roads _________________________ 11 Table 6.1: Thetford ATC Trip Rates per Site for Peak Periods (per unit) ________________________________ 12 Table 6.2: Comparison of Peak Period Trip Rates between TRICS and ATC data (per unit) _________________ 13 Table 6.3: Difference between ATC and TRICS Trip Rates for Peak Periods (per unit) _____________________ 13 Table 6.4: Comparison of Housing Density between ATC Sites and TRICS Site __________________________ 13 233902/BSE/NOR/5-1/C 21 February 2011
Transport Plan for Thetford
Highway Interventions
Table 6.5: Comparison of Housing Type and Price Range (Source: www.rightmove.co.uk/house-prices.html) ___ 13
Table 6.6: Redistribution of Cycling and Walking Trips to derive Car Driver Trips _________________________ 14
Table 6.7: Journey to Work Data – External Destination/Origin Proportions ______________________________ 15
Table 6.8: Residential Generated Traffic Peak Period Trips (journeys to work) ___________________________ 16
Table 6.9: Residential Generated Traffic Peak Period Trips (non-journeys to work) ________________________ 16
Table 6.10: Distribution of non-journeys to work ____________________________________________________ 16
Table 6.11: TRICS Trip Rate for Peak Periods (per unit) _____________________________________________ 17
Table 6.12: Total Employment Trips for Peak Periods for 2,000 jobs ____________________________________ 17
Table 6.13: Distribution of Employment Generated Traffic AM Peak Period _______________________________ 20
Table 6.14: Distribution of Employment Generated Traffic PM Peak Period _______________________________ 20
Table 8.1: ARCADY Output A11 / A1075 (London Road) Roundabout 2026 _____________________________ 33
Table 8.2: ARCADY Output A11 / B1107 (Brandon Road) Roundabout 2026 ____________________________ 35
Table 8.3: ARCADY Output for A11 / Mundford Road Junction 2026 ___________________________________ 36
Table 8.4: PICADY Output for A11 Slip / Croxton Road North Junction 2026_____________________________ 37
Table 8.5: PICADY Output for A11 Slip / Croxton Road South Junction 2026 ____________________________ 38
Table 8.6: ARCADY Output for A11 / Norwich Road Junction 2026 ____________________________________ 39
Table 9.1: PICADY / LINSIG Output for Mundford Road / Croxton Road Junction 2026_____________________ 42
Table 9.2: LINSIG Output Brandon Road, Bury Road and London Road 2026 Base Scenario _______________ 43
Table 9.3: ARCADY Output for Norwich Road / Mundford Road / Hurth Way Junction 2026 _________________ 44
Table 9.4: ARCADY Output for Hurth Way / A1066 / A1088 and Castle Street Junction 2026 ________________ 45
Table 10.1: Cost Estimates ____________________________________________________________________ 47
Table D.1: Before Application of Smarter Choices Reductions ________________________________________ 68
Table D.2: After Application of Smarter Choices reductions __________________________________________ 68
Table D.3: Before Application of Smarter Choices Reductions ________________________________________ 69
Table D.4: After Application of Smarter Choices Reductions__________________________________________ 69
Table D.5: Total Traffic via A11 before Application of Smarter Choices Reductions ________________________ 69
Table D.6: Total Traffic via A11 After Application of Smarter Choices Reductions _________________________ 69
Table D.7: Total Traffic Removed from A11_______________________________________________________ 70
Figures
Figure 3.1: 2009 Base Scenario – Turning Movement Diagram AM Peak Hour_____________________________ 5
Figure 3.2: 2009 Base Scenario – Turning Movement Diagram PM Peak Hour_____________________________ 6
Figure 4.1: 2026 Base Scenario – Turning Movement Diagram AM Peak Hour_____________________________ 9
Figure 4.2: 2026 Base Scenario – Turning Movement Diagram PM Peak Hour____________________________ 10
Figure 6.1: Residential Generated Traffic Flows AM Peak Hour (All Trip Purposes) ________________________ 18
Figure 6.2: Residential Generated Traffic Flows PM Peak Hour (All Trip Purposes) ________________________ 19
Figure 6.3: External Trips Generated by Employment Sites within Thetford AM Peak Hour – Turning Movement
Diagram showing Arrivals and Departures to SUE, TEP and Town ____________________________ 21
Figure 6.4: External Trips Generated by Employment Sites within Thetford PM Peak Hour – Turning Movement
Diagram showing Arrivals and Departures to SUE, TEP and Town ____________________________ 22
Figure 6.5: 2026 Peak Hour Growth Factor Calculations _____________________________________________ 23
Figure 6.6: Turning Movement Diagram 2026 AM Peak Hour Baseline with SUE Development Generated Traffic
Flows (All Trip Purposes) with Link Capacity _____________________________________________ 25
Figure 6.7: Turning Movement Diagram 2026 PM Peak Hour Baseline with SUE Development Generated Traffic
Flows (All Trip Purposes) with Link Capacity _____________________________________________ 26
Figure 7.1: Turning Movement Diagram 2026 AM Peak Hour Baseline with SUE Development Generated Traffic
Flows and Soft Measures (Includes All Trips from the SUE) with Link Capacities _________________ 28
Figure 7.2: Turning Movement Diagram 2026 PM Peak Hour Baseline with SUE Development Generated Traffic
Flows and Soft Measures (Includes All Trips from the SUE) with Link Capacities _________________ 29
233902/BSE/NOR/5-1/C 21 February 2011Transport Plan for Thetford Highway Interventions 233902/BSE/NOR/5-1/C 21 February 2011
Transport Plan for Thetford
Highway Interventions
Executive Summary
Thetford has achieved Growth Point Status, and so is targeted to experience
considerable growth over the period to 2026. Meeting the growth targets will involve
supporting infrastructure. In order to accommodate this growth in a sustainable manner
and as part of the development of the Thetford Area Action Plan and the Moving Thetford
Forward initiative, a Transport Plan for Thetford is being developed.
As part of this Transport Plan for Thetford, this report has been prepared to provide an
overview of the highway capacity work and the assumptions made and assessments
carried out are set out in this report.
Assessments have been carried out to assess the impacts of the proposed TAAP on
existing junctions and internal links within Thetford area and at five A11 junctions.
Overall it is concluded that the proposed TAAP will have an impact on the operation of
the local highway network, however the work has shown that the majority of junctions are
forecast to be operating over their theoretical capacity without development generated
traffic.
A VISSIM model has been produced for 5km of the A11 at Thetford to provide further
traffic assessments at the five junctions with the A11. The results of the VISSIM
modelling are provided in Mott MacDonald ‘A11 VISSIM Scenario Modelling Report’,
which should be read in conjunction with this report.
This Report concludes that:
Improvements to two links, Mundford Road and Norwich Road, are recommended to
increase capacity and reduce congestion on the network;
Junction improvements are required at Bury Road / London Road, Croxton Road /
Mundford Road junction and Norwich Road / Hurth Way junction; and
Junction improvements are required at all five points of contact with the A11. Although
localised junction assessments using ARCADY or PICADY show that some of these
junctions would operate below capacity with the ‘Low Level Network Mitigation’
proposals, further assessments using VISSIM predict that signalisation would be
required.
233902/BSE/NOR/5-1/C 21 February 2011
C:\DOCUME~1\jol05796\OTLocal\PIMSLI~1\Workbin\57A697FC.R.O\Highway Interventions Rep 5-1C.doc
iTransport Plan for Thetford
Highway Interventions
1. Introduction
1.1 Purpose of this Report
This report has been prepared by Mott MacDonald to provide an overview of the highway capacity work
that has been undertaken as part of the Transport Plan for Thetford.
This report provides details of traffic survey and Base Scenario assumptions. It also provides a description
of the capacity assessments that have been undertaken in relation to future growth in the town, associated
with the Thetford Area Action Plan (TAAP). The forecast effects of the TAAP on traffic flows within the
town and on the A11 have been analysed using operational capacity assessments at a total of 9 junctions.
A series of mitigation measures and interventions have been developed and tested in order to
accommodate the likely increase in traffic flows.
Mott MacDonald has produced a VISSIM model for the 5km length of the A11, the Thetford bypass. The
results of the VISSIM modelling are provided in a separate report, which should be read in conjunction with
this report.
1.2 Report Structure
The remainder of this report is structured as follows;
Section 2 provides an overview of the baseline traffic data, including details of the surveys carried out;
Section 3 summarises the assumed existing traffic and the surrounding highway network considered for
the Base Scenario;
Section 4 demonstrates how baseline traffic data has been growthed to the TAAP target year of 2026
using TEMPRO;
Section 5 provides an introduction to the link capacity assessment work that has been undertaken;
Section 6 describes how development generated traffic associated with the TAAP growth has been
generated and details how this traffic has been distributed on the highway network for the Do-Minimum
Scenario;
Section 7 provides details of the Do-Something Scenario and outlines the results of link capacity
assessment work that has been undertaken;
Section 8 shows the impact of the anticipated development on the A11 highway junctions and outlines
potential interventions;
Section 9 shows the impact of the anticipated development on the internal highway junctions and
outlines potential interventions;
Section 10 details initial intervention costing work that has been undertaken; and
Section 11 provides a summary and the conclusions to the report.
233902/BSE/NOR/5-1/C 21 February 2011
1Transport Plan for Thetford
Highway Interventions
2. Baseline Traffic Data
2.1 Introduction
To assess the operation of the existing highway network within Thetford and the immediate surrounds a
series of traffic surveys were undertaken by Count on Us, between December 2009 and January 2010.
Surveys were undertaken both within Thetford and at the 5 junctions which link the town with the A11 to the
north and west.
This Section details the surveys that have been undertaken and the associated methodology that was
applied.
2.2 Traffic Surveys
A mixture of Origin-Destination information, turning count data, HGV counts and queue length data was
obtained. The various traffic surveys undertaken were split into separate work packages and conducted
over alternate days to expedite the survey process. A plan showing the location of all of the survey sites is
provided at Appendix A.
All of the surveys undertaken were conducted on typical weekdays, for the assumed morning peak period
(between 07:00 and 10:00) and for the assumed evening peak period (between 15:00 and 18:00) unless
stated below. The Sustainable Urban Extension (SUE) development that is proposed is likely to have less
impact on the local highway network during the inter-peak period, so therefore this period has been
excluded for the purpose of this study.
It has been agreed with both Norfolk County Council and the Highways Agency that the surveys which
have been undertaken are sufficient for the purpose of this study.
2.2.1 Automatic Number Plate Recognition Surveys (ANPR) and Manual Classified
Counts (MCC)
To provide a count of all vehicle turning movements and to better understand the levels of queuing and
lane allocation at junctions on the A11 and within the town, ANPR and MCC surveys were undertaken at
the following junctions;
A11 Junctions
A11 London Road – a 3-arm at-grade roundabout;
A11, B1107 Brandon Road – a 4-arm at-grade roundabout;
A11, A134, A1066 Mundford Road – a 4-arm at-grade roundabout;
A11, Croxton Road – a grade separated junction; and
A11, A1075 Norwich Road – a 4-arm at-grade roundabout.
Junctions within Thetford
London Road and Brandon Road – a 4-arm signalised junction;
Croxton Road and Mundford Road – a T-junction with a ghost island provided on Mundford Road for
traffic turning right into Croxton Road;
Norwich Road, Hurth Way and Mundford Road – a 4-arm roundabout; and
Hurth Way, Castle Street, A1066 and A1088 – a 4-arm roundabout.
233902/BSE/NOR/5-1/C 21 February 2011
2Transport Plan for Thetford
Highway Interventions
The proportion of HGV movements was also captured using manual classified counts at all of the junctions
detailed.
2.2.2 Cordon Automatic Traffic Counts (ATC)
ATC surveys were undertaken over a two week period in January 2010, at four residential sites within
Thetford, all of which have one vehicular access junction linking to the surrounding highway network. This
data was used to determine trip rates to and from the proposed SUE. Data from the counters has been
analysed for two typical weekdays (Tuesday 26 January 2010 and Wednesday 27 January 2010).
Data has been analysed for the morning and evening peak periods and for the daily profile at the sites.
The four sites surveyed were;
Woodlands Drive – Approximately 504 residential units;
Arlington Way – Approximately 92 residential units;
Nunnery Drive – Approximately 124 residential units and;
Maine Street – Approximately 120 residential units.
Further details relating to the calculation of trip rates is included under heading 6.2.
2.2.3 Road Side Interview Surveys (RSI)
Two directional RSIs were undertaken on the 7 strategic radial routes which provide access to the town, on
5 neutral days from Thursday 10 to Thursday 17 December 2009. These surveys were only conducted for
the morning peak period (07:30-09:30) due to lack of sufficient daylight during the evening peak period and
subsequent safety concerns.
These surveys were undertaken to better understand the origin and destination of traffic within the town, to
provide an indication of journey purpose and the proportion of journeys to/from work.
The RSI corridors comprise;
A1066 Mundford Road;
C107 Croxton Road;
Hurth Way;
A134 Bury Road;
C587 London Road; and
A134 Brandon Road.
2.3 Peak Hours
The survey data peak hours have been determined to be from 08:00-09:00 for the morning peak period and
from 17:00-18:00 for the evening peak period, which mirror the network peak hours.
233902/BSE/NOR/5-1/C 21 February 2011
3Transport Plan for Thetford
Highway Interventions
3. Base Scenario
3.1 Introduction
Existing traffic flows at the 9 junctions within Thetford and its surround have been obtained from the manual
classified turning count and ANPR surveys that were undertaken by Count on Us, as detailed in Section 2.
These traffic flows have been used to produce turning movement diagrams at each of the 9 junctions
surveyed for both the AM and PM peak periods.
The Base Scenario reflects the current situation on the highway network in and around Thetford and does
not include any additional trips that would be generated by the planned growth as set out in the Thetford
Area Action Plan (TAAP).
3.2 Assessment Methodology
The Base Scenario has been tested to investigate how the 9 junctions are currently operating in terms of
capacity and levels of queuing.
All roundabout junctions have been assessed using ARCADY version 6, which is recognised by the
Department for Transport for the modelling of roundabouts. The Croxton Road / Mundford Road priority
junction and both of the A11 / Croxton Road slips have been assessed using PICADY version 4.1, which is
recognised by the Department for Transport for the modelling of priority junctions. The roundabout and
priority junctions have been assessed in terms of the level of queuing and the Ratio of demand Flow to
Capacity (RFC). Typically the maximum desired threshold for RFC is 0.85, which is equivalent to 85% of
the theoretical capacity.
The London Road / Brandon Road junction has been assessed using LINSIG version 3, which is
recognised by the Department for Transport as software for the modelling of signalised junctions.
Signalised junctions are assessed in terms of their Degree of Saturation (DoS) which represents the ratio of
demand to capacity on each approach, with a value of 100% meaning that demand and capacity are equal.
It is typically considered that 90% is the threshold, when values are above this level it is felt that the
junction is reaching capacity and congestion and queues start to form.
The ARCADY, PICADY and LINSIG runs that have been undertaken as part of this study are based on
geometry obtained from an OS base map. Use of this is likely to lead to a higher, but not quantifiable,
margin of error than geometry from topographical plans; however, these surveys have not been undertaken
as part of this study. All of the models have been validated by comparing queue length data from the traffic
surveys with forecast queues taken from the model run outputs.
To calibrate the ARCADY models, the initial Base Scenario run has been amended to reflect unequal lane
usage by adjusting the intercept values on certain arms. These models have then been re-run and the
results from the baseline assessments for both peak periods are provided within Sections 7 and 8.
Base Scenario turning movement diagrams which provide a count of the directional movement of vehicles
through each junction for both the AM and PM peak hours have been produced and are based on the
obtained survey data; these are provided in Figures 3.1 and 3.2.
233902/BSE/NOR/5-1/C 21 February 2011
4Transport Plan for Thetford
Highway Interventions
Figure 3.1: 2009 Base Scenario – Turning Movement Diagram AM Peak Hour
233902/BSE/NOR/5-1/C 21 February 2011
5Transport Plan for Thetford
Highway Interventions
Figure 3.2: 2009 Base Scenario – Turning Movement Diagram PM Peak Hour
233902/BSE/NOR/5-1/C 21 February 2011
6Transport Plan for Thetford
Highway Interventions
4. TEMPRO Growth Factor
4.1 Trip Growth Assumptions
The assumed year of full occupation of the SUE is 2026, forecasting has been based on applying growth
factors from the TEMPRO version 6.2 database, reflecting the government’s National Trip End Model
version 5.4 (NTEM) of traffic growth.
Growth factors have been applied to the 2009 baseline data to derive 2026 ‘do-nothing’ traffic movements.
To calculate the ‘localised’ growth factor for Thetford for 2026, the local factors from TEMPRO have been
applied to the growth factors from the NRTF. The TEMPRO growth adopted for the 2026 Scenarios are
shown in Table 4.1.
Table 4.1: TEMPRO Growth Factors
Period 2009 - 2026
AM Peak Period 1.216
PM Peak Period 1.250
Source: TEMPRO Version 6.2
Further analysis of the TEMPRO forecast data has been undertaken to identify if the SUE has been
included as part of the future development, within the TEMPRO growth calculations. This work is important
to avoid ‘double counting’ development traffic when modelling future year Scenarios.
Data obtained from the Regional Spatial Strategy for the East of England is included in Table 4.2. It shows
that in Thetford it is envisaged that there will be an additional 816 new trips per day as a result of future
residential development within the town. In comparison, data from TEMPRO shown in Table 4.3 indicates
that there will be an additional 157 trips per day, which suggests that the additional housing growth ie the
SUE has not been included within the TEMPRO growth calculations.
Table 4.2: Regional Spatial Strategy Data
RSS
Dwellings to be delivered 6,000
Dwelling still to be delivered 4,896 (408 per year)
Daily trips (based on 2 trips per household) 816
Source: TEMPRO and East of England Regional Spatial Strategy
The TEMPRO future daily trips have been derived by calculating the growth factor for car drivers for an
average weekday, each year from 2009 up to the year of 2021 as shown in Table 4.3.
Table 4.3: TEMPRO Growth Factors for Car Drivers (Average Weekday – Thetford) 2009 - 2021
All Purposes Percentages
Years
Production Attraction Production Attraction
2009 - 2010 1.0118 1.0114 1.18% 1.14%
2010 - 2011 1.0117 1.0113 1.17% 1.13%
2011 - 2012 1.0086 1.0096 0.86% 0.96%
2012 - 2013 1.0086 1.0095 0.86% 0.95%
2013 - 2014 1.0085 1.0094 0.85% 0.94%
233902/BSE/NOR/5-1/C 21 February 2011
7Transport Plan for Thetford
Highway Interventions
All Purposes Percentages
2014 - 2015 1.0084 1.0093 0.84% 0.93%
2015 - 2016 1.0083 1.0092 0.83% 0.92%
2016 - 2017 1.0070 1.0075 0.70% 0.75%
2017 - 2018 1.0070 1.0074 0.70% 0.74%
2018 - 2019 1.0069 1.0074 0.69% 0.74%
2019 - 2020 1.0069 1.0073 0.69% 0.73%
2020 - 2021 1.0068 1.0073 0.68% 0.73%
Source: TEMPRO
The growth factors have then be calculated into additional car driver trips per year by deducting future year
from the base year and then an average has been taken which represents additional car driver trips
(production minus attraction) as shown in Table 4.4.
Table 4.4: Average Weekday Trips by Car Drivers (future year minus base year)
All Purposes
Years
Production Attraction
2009 - 2010 211 228
2010 - 2011 211 228
2011 - 2012 158 196
2012 - 2013 158 196
2013 - 2014 158 196
2014 - 2015 158 196
2015 - 2016 158 196
2016 - 2017 134 161
2017 - 2018 134 161
2018 - 2019 134 161
2019 - 2020 134 161
2020 - 2021 134 161
Average 157 187
Source: TEMPRO
A comparison of Tables 4.2 and 4.4 suggests that TEMPRO has significantly underestimated the level of
growth likely to occur in Thetford. TEMPRO anticipates there will be an additional 157 daily trips per day
generated by the Thetford area in 2021. Whilst analysis of the RSS housing and employment targets for
the Thetford area indicate an additional 816 daily trips per year (Table 4.2), suggesting that TEMPRO has
not taken the majority of the proposed additional growth outlined in the RSS into account when calculating
growth factors.
It is therefore assumed that the TEMPRO growth reflects the ‘infill development’ of approximately 1,073
new residential dwellings to be constructed in the existing urban area of Thetford between 2007 and 2015
and no further numerical allowance has been made for this.
2026 Base scenario traffic flows for AM and PM peaks are shown in Figures 4.1 and 4.2 below. The 2026
Base Scenario reflects the current situation on the highway network in and around Thetford factored up by
background growth factors to 2026 and does not include any additional trips that would be generated by
the planned growth in the SUE.
233902/BSE/NOR/5-1/C 21 February 2011
8Transport Plan for Thetford
Highway Interventions
Figure 4.1: 2026 Base Scenario – Turning Movement Diagram AM Peak Hour
3.19% to Watton A1075
to Croxton
to King's Lynn
7.71%
N NE to Norwich
NW
1.216318 GF 181 198 1
A134
2
218 313 94 0 122
4
24 4 58 19 916
150 1162
91 28
882 348
1216
307 75 35 34 125 35
199 1 126
225 249
0
270 26
14.69%
to Brandon B1107
133
451
94 170
58 128 140
524 536
159 362 342
361
687 409
133 1293 281 358 158
91 242
113 504 A1066
362
96
19
324 78 285 259
34 887 23 21
114
193 276 176
50
100 309 35 490 356 246 A1066
114 36
to Diss
1046 342
178
A1075
103 235 13 191
2.42%
9
791 199 158 201 10.08%
A1088
34.96% A11 to Ixworth
to Cambridge A134
18.13%
to Bury St Edmunds
233902/BSE/NOR/5-1/C 21 February 2011
9Transport Plan for Thetford
Highway Interventions
Figure 4.2: 2026 Base Scenario – Turning Movement Diagram PM Peak Hour
3.19% to Watton A1075
to Croxton
to King's Lynn
7.71%
N NE to Norwich
NW
1.250081 GF 86 141 4
A134
19
106 245 80 0 234
1
73 4 38 3 1218
196 843
76 60
1320 295
801
263 191 18 44 54 38
70 4 183
304 320
0
325 38
14.69%
to Brandon B1107
215
720
30 219
44 156 170
396 466
145 230 316
400
399 480
151 950 209 324 324
114 613
254 460 A1066
236
80
28
289 148 280 245
118 1304 36 84
146
464 309 359
34
145 376 71 295 276 261 A1066
126 34
to Diss
750 214
149
A1075
66 303 6 61
2.42%
4
1123 305 420 166
10.08%
A1088
34.96% A11 to Ixworth
to Cambridge A134
18.13%
to Bury St Edmunds
233902/BSE/NOR/5-1/C 21 February 2011
10Transport Plan for Thetford
Highway Interventions
5. Link Capacities
5.1 Introduction
Maximum hourly vehicle capacity for urban trunk roads has been calculated for the various link roads in
Thetford. These have been calculated based on data from the Design Manual for Roads and Bridges
TA79/99 Traffic Capacity of Urban Roads.
The link capacities included in TA79/99 are based primarily on the total number of lanes, carriageway width
and road features (ie speed limit, side roads, parking and pedestrian crossings). Capacity of urban roads
can be affected by a wide range of factors that may not always be accurately predicted by the road features
identified. For this reason capacity flows may be up to 10% more or less than the values provided in
TA79/99. Flows for single carriageway roads are also based upon a 60/40 directional split in the flow.
5.2 Assumed Link End Capacities for Thetford
Table 5.1 shows the maximum capacities of the urban roads within Thetford, based on one-way hourly
flows in each direction at the various link ends.
Table 5.1: Hourly One-way Link End Capacities for Thetford Urban Trunk Roads
Carriageway Maximum One-
Road Link Road Type
Width way Hourly Flows
Norwich Road approach to A11 UAP 1 7.3m 1,590
Norwich Road North approach to Norwich Road (town centre) UAP 3 7.3m 1,300
Hurth Way approach to Mundford Road UAP 2 7.3m 1,470
Hurth Way approach to A1088 UAP 2 7.3m 1,470
Mundford Road approach to Hurth Way UAP 1 9.0m 1,860
Mundford Road East approach to Croxton Road UAP 1 9.0m 1,860
Mundford Road West approach to Croxton Road UAP 2 6.75m 1,260
Croxton Road approach to Mundford Road UAP 3 6.1m 900
Croxton Road approach to A11 UAP 4 9.0m 1,320
Mundford Road approach to A11 UAP 2 6.75m 1,260
Brandon Road approach to A11 UAP 3 7.3m 1,300
Brandon Road approach to Bury Road UAP 3 7.3m 1,300
Norwich Road (town centre) approach to Norwich Road North UAP 3 6.75m 1,110
Norwich Road (town centre) approach to London Road UAP 3 6.75m 1,110
London Road approach to Norwich Road UAP 2 7.3m 1,470
London Road approach to A11 UAP 2 7.3m 1,470
(UAP = Urban All-Purpose Road)
A Link Capacity Appraisal has been undertaken within Section 7 of this report, for both the 2026
background traffic with Development Scenario and the 2026 background traffic with development and soft
measures Scenario based on the maximum capacities provided in Table 5.1.
233902/BSE/NOR/5-1/C 21 February 2011
11Transport Plan for Thetford
Highway Interventions
6. Do-Minimum Scenario
6.1 Introduction
This is the scenario that would arise if the planned growth of new homes and associated employment
development were to occur with no improvements being made to the transport network to mitigate the
impact of the additional journeys. This scenario also includes the impact of general growth in vehicle trips
brought about by growth outside Thetford up to 2026.
Residential and employment development generated traffic between the SUE, internal and external
destinations have been calculated, based on a number of assumptions which are detailed within this
Section.
6.2 Trip Rate Calculations
6.2.1 Residential Trip Rates
As detailed under heading 2.2.2, ATC surveys were undertaken over a two week period in January 2010, at
four residential sites within Thetford in order to derive trip rates for the SUE; these were compared against
those previously obtained from the TRICS database. The estates surveyed are accessed via;
Woodlands Drive – Approximately 504 units;
Arlington Way – Approximately 92 units;
Nunnery Drive – Approximately 124 units; and
Maine Street – Approximately 120 units
Table 6.1 shows a comparison of trip rates between the four ATC sites within Thetford.
Table 6.1: Thetford ATC Trip Rates per Site for Peak Periods (per unit)
AM Peak PM Peak
ATC Site Location
Arrivals Departures Arrivals Departures
Woodlands Drive 0.193 0.459 0.608 0.338
Arlington Way 0.620 0.587 0.810 0.353
Nunnery Drive 0.153 0.569 0.694 0.294
Maine Street 0.104 0.221 0.267 0.113
Table 6.1 shows that trip rates are similar between two of the four sites, with the exception of Maine Street
and Arlington Way. Maine Street has significantly lower vehicle trip rates than the other three sites in all of
the peaks, which could be because Maine Street is a United States Air Force housing development.
Trip rates from Arlington Way have also been discounted, as there are significantly more arrivals in both
the AM and PM peak hours at this site. The survey team feel that this could be due to counters not picking
up or double counting vehicles at the site, due to queuing or vehicles travelling under 10mph. For these
reasons, trip rates for Maine Street and Arlington Way have been discounted in the analysis provided in
Tables 6.2 and 6.3. Tables 6.2 and 6.3 show a comparison between the average ATC trip rates for
Thetford and the previously derived TRICS trip rates for the site at Bury St Edmunds for both the AM and
PM peak periods.
233902/BSE/NOR/5-1/C 21 February 2011
12Transport Plan for Thetford
Highway Interventions
Table 6.2: Comparison of Peak Period Trip Rates between TRICS and ATC data (per unit)
AM Peak PM Peak
ATC Site Location
Arrivals Departures Arrivals Departures
Average ATC trip rates 0.173 0.514 0.651 0.316
TRICS trip rates 0.109 0.554 0.525 0.228
Table 6.3: Difference between ATC and TRICS Trip Rates for Peak Periods (per unit)
AM Peak PM Peak
ATC Site Location
Arrivals Departures Arrivals Departures
Difference between ATC and
0.064 -0.040 0.126 0.088
TRICS data
Tables 6.2 and 6.3 show trip rates from the ATC sites in Thetford are typically higher than the TRICS data,
with the exception of departures in the AM peak which are marginally lower. There are a number of
possible reasons why the trip rates from the ATC counters and the TRICS database varies, including;
The TRICS survey was undertaken on 15 May 2006, approximately four years ago and it is possible
that trip rates and travel behaviour at the site may have changed. In comparison, the ATC surveys at
the residential sites in Thetford were undertaken in January 2010.
The difference between the times of year that the surveys were undertaken (May and January)
Table 6.4 shows the difference in housing density between the Thetford sites and the Bury St Edmunds
site (densities for the Thetford sites are approximate). Table 6.4 shows that the TRICS site has a higher
density of housing per hectare compared each of the Thetford ATC sites which could impact on trip
rates.
Table 6.4: Comparison of Housing Density between ATC Sites and TRICS Site
Site Location Approximate Units Approximate Hectares Dwellings per Hectare
Woodlands Drive 504 20.2 25
Nunnery Drive 124 8.3 15
Thetford Sites Average 314 14.3 22
Bury St Edmunds TRICS Site 101 3.6 28
An analysis of the type and tenure of housing between the ATC site and the TRICS sites has been
undertaken and is summarised in Table 6.5.
Table 6.5: Comparison of Housing Type and Price Range (Source: www.rightmove.co.uk/house-prices.html)
Site Location Predominant Type Predominant Tenure Price Range £
Mixed (Terraced / Detached /
Woodlands Drive Freehold / Leasehold 50,000 – 184,000
Semi - Detached
Nunnery Drive Detached Freehold 185,000 – 215,000
TRICS Site Semi - Detached Freehold 165,000 – 188,000
It is not possible for trip generation rates at a new development site to be 100% accurate. The TRICS
database is surveys from various sites used to estimate what the likely trip rates will be for similar sites.
The previously derived TRICS site has very similar trip rates to those surveyed in Thetford.
233902/BSE/NOR/5-1/C 21 February 2011
13Transport Plan for Thetford
Highway Interventions
To ensure that the trips generated by the proposed residential aspect of the SUE reflect local conditions,
the trip rates obtained from the ATC survey data have been used to model the SUE residential areas in
Thetford for all future year Scenarios.
6.2.2 Employment Trips – Mode Share
Mode share for trips from external destinations outside Thetford, arriving and departing at the SUE
employment sites have been calculated based on 2001 census data, using travel to work data for the
Lower Super Output Areas within the parish of Thetford.
To derive car driver based trips, walking and cycling trips have been redistributed proportionally into car
driver, bus, train or car passenger based trips as these other modes are unlikely to be used to travel to
Thetford from external destinations, the initial and adjusted mode share percentages are shown in
Table 6.6.
Table 6.6: Redistribution of Cycling and Walking Trips to derive Car Driver Trips
Mode Census Mode Share % Adjusted Mode Share % Adjusted Mode Share Rates
Walking 16.07 - -
Cycling 4.95 - -
Car Driver 67.79 88.19 1893
Bus 1.34 1.75 38
Train 0.22 0.28 6
Car Passenger 7.52 9.78 210
Other 2.11 - -
Total Trips 100 100 2146
Source: Office for National Statistics 2001 Census Data
Table 6.6 shows that 88.19% of adjusted trips are classified as car driver trips. This mode share figure has
been used for all external car driver journeys to and from the employment sites within the SUE (0.882).
6.3 SUE Residential Generated Traffic
In total the impact of some 5,900 additional dwellings have been factored into the assessment of conditions
on the transport network in 2026. Predicted residential development generated traffic flows have been
derived based on the number of dwellings allocated each side of the railway. It has been agreed that
33.33% of dwellings will be located to the west of the railway line (SUE West) and the remaining 66.67%
will be located to the east of the railway line (SUE East).
6.3.1 Traffic Flows
Data from the roadside interview (RSI) surveys has been analysed and shows that 71% of trips were
classified as journeys to work. The remaining 29% of trips are for other purposes.
For this study all trips between the SUE and other parts of Thetford have been assumed to be to and from
the town centre, expect for those to the TEP.
233902/BSE/NOR/5-1/C 21 February 2011
14Transport Plan for Thetford
Highway Interventions
6.3.2 Distribution on the Network
Traffic flows between the SUE and external destinations outside Thetford have been distributed based on
journey to work census 2001 data, as shown in Table 6.7. It is assumed that the growth areas do not
change the census 2001 journey to work pattern for the purpose of this study.
Table 6.7: Journey to Work Data – External Destination/Origin Proportions
Direction of Proportion (%)
Norwich 8.82
Watton 3.19
King’s Lynn 7.71
Brandon 14.69
Cambridge 34.96
Bury St Edmunds 18.13
Ixworth 10.08
Diss 2.42
Of the 71% of trips which are journeys to work, it has been assumed that of those generated by the SUE,
60% are internal trips within Thetford and the remaining 40% are to destinations outside of Thetford (as
determined from the 2001 census).
Of this 60% of trips generated by the SUE to internal destinations within Thetford, it was initially proposed
to distribute these based on allocating specific proportions of traffic between 3 specific employment
locations within the town;
Proposed Thetford Enterprise Park – 1,500 jobs – 30% of internal trips;
Contained within the Town Centre – 1,000 jobs – 20% of internal trips ; and
Contained within the SUE site – 2,500 jobs – 50% of internal trips
Following detailed discussions with officers from Norfolk County Council Developer Services, it was agreed
to model a worse case scenario ie a reduced level of containment at the SUE;
A split of 50% to the town centre, 30% to the TEP with only 20% containment within the SUE, ie
increasing the number of trips on the network and providing a worse case Scenario.
It has been assumed that internal trips with an origin and destination within the SUE (ie 20% of internal
trips) will travel within the SUE and have therefore not been distributed onto the highway network for the
purpose of this study.
Initial link capacity work undertaken with traffic in 2026 indicated that Norwich Road, either side of its
junction with Hurth Way, to the east of the town centre was significantly above its theoretical capacity, the
links to the west of the town centre were below their theoretical capacity. Therefore, to better reflect the
likely distribution of traffic to the town centre, it has been distributed with 50% via the A11, Brandon Road
and the signalised junction of Norwich Road / Bury Road / London Road / Brandon Road and 50% via the
Norwich Road / Hurth Way junction.
It has also been assumed that traffic arriving and departing from the Thetford Enterprise Park (TEP) will do
so via the A11, at the nearest appropriate junction from the SUE. Trips between the TEP and Bury St
Edmunds have been distributed via the A11 and not the town centre because it is considered that it is more
233902/BSE/NOR/5-1/C 21 February 2011
15Transport Plan for Thetford
Highway Interventions
likely that vehicles would use the A11 to access the TEP from Bury St Edmunds, rather than intersecting
the town centre, where delays are more likely to occur due to congestion.
Table 6.8 shows the number of car driver trips that have been distributed from the SUE residential sites
onto the local highway network for journeys to work (ie 71%).
Table 6.8: Residential Generated Traffic Peak Period Trips (journeys to work)
AM Peak PM Peak
Plot In Out In Out
West of the railway line 240 714 904 439
East of the railway line 480 1,427 1,808 878
TOTAL 720 2,141 2,712 1,317
6.3.3 Non-Journey to Work Vehicle Trips
To capture the remaining 29% of car trips generated by the residential aspect of the SUE development in
the peak hours, that are not journeys to work, it has been assumed that all non-work trips either remain
within the SUE (50%), or are between the SUE and the town centre (50%).
The total non-journey to work trips generated by the SUE (29.4%) are detailed in Table 6.9 for both the AM
and PM peak hours.
Table 6.9: Residential Generated Traffic Peak Period Trips (non-journeys to work)
AM Peak PM Peak
Plot In Out In Out
West of the railway line 100 297 376 183
East of the railway line 200 595 753 366
TOTAL 300 892 1,129 548
The non-journey to work trips shown in Table 6.9 have then been distributed either within the SUE (50%),
or distributed onto the network and arriving/departing the town centre (50% via the A11 and 50% via the
Hurth Way / Mundford Road junction), as shown in Table 6.10.
Table 6.10: Distribution of non-journeys to work
AM Peak PM Peak
In Out In Out
Town Town Town Town
Plot SUE Centre SUE Centre SUE Centre SUE Centre
West of the
49 51 148 150 187 189 90 92
railway line
East of the
99 101 296 298 376 378 181 183
railway line
41 42 123 124 156 157 75 76
58 59 173 174 220 221 106 107
TOTAL 148 152 444 448 563 567 271 275
Traffic flows generated by the new residential development in the SUE are shown in Figures 6.1 and 6.2
below.
233902/BSE/NOR/5-1/C 21 February 2011
16Transport Plan for Thetford
Highway Interventions
6.4 TAAP Employment Generated Traffic
It has been assumed that the TAAP employment sites will generate a proportion of trips from outside
Thetford. These employment sites are:
• At the TEP;
• Within the SUE; and
• In the town centre, representing growth in the retail and local authority sectors, etc.
To capture these trips it has been assumed that the proportion of trips out of Thetford would mirror the
proportion commuting into the town (ie 40%). Therefore, of the 5,000 jobs contained within the town’s
employment sites, 2,000 of these will be filled by external commuters.
The TRICS 2010 (a) database has been interrogated to determine appropriate trip rates which have been
discussed and agreed with the Highways Agency, their consultant, AECOM, and Norfolk County Council.
Table 6.11: TRICS Trip Rate for Peak Periods (per unit)
AM Peak PM Peak
Site Location
Arrivals Departures Arrivals Departures
Welshpool Road, Shrewsbury 0.530 0.147 0.157 0.548
The survey site used in TRICS has been analysed to ensure that it accurately reflects the proposed SUE
development site. The TRICS site is a B1 business park located in Shrewsbury, Shropshire (reference SH-
02-B-01) and was selected through discounting the region of Greater London as an initial parameter,
before removing town centre sites and industrial zones.
Table 6.11 shows that TRICS anticipates that there will be 0.147 departures in the AM peak per job and
0.157 arrivals in the PM peak per job, ie an average rate of 0.152, which it is proposed to use. However,
this does not account for departures in the AM peak period and arrivals in the PM peak period related to
the other 3,000 jobs serviced by people living in the SUE, which would generate an additional 456
movements, ie totals of 760. Table 6.12 shows the total number of external trips based on the trip rates
provided in Table 6.11 for the proposed additional 2,000 jobs within Thetford that will be taken by external
commuters.
Table 6.12: Total Employment Trips for Peak Periods for 2,000 jobs
AM Peak PM Peak
Method
Arrivals Departures Arrivals Departures
TRICS 1060 294 314 1096
Figures used 1058 760 760 1058
233902/BSE/NOR/5-1/C 21 February 2011
17Transport Plan for Thetford
Highway Interventions
Figure 6.1: Residential Generated Traffic Flows AM Peak Hour (All Trip Purposes)
233902/BSE/NOR/5-1/C 21 February 2011
18Transport Plan for Thetford
Highway Interventions
Figure 6.2: Residential Generated Traffic Flows PM Peak Hour (All Trip Purposes)
233902/BSE/NOR/5-1/C 21 February 2011
19Transport Plan for Thetford
Highway Interventions
6.4.1 Distribution on the Network
Traffic generated by the TAAP employment sites has been distributed based on census 2001 journey to
work data. Traffic has been distributed between the external entry points and the employment locations;
town centre (TC), TEP and SUE, and proportions have been reversed to reflect departures from the
employment sites. The same assumptions used for the residential trip distribution have been applied.
Tables 6.13 and 6.14 show how the car trips have been distributed between the four recognised
employment sites in both of the peak periods.
Table 6.13: Distribution of Employment Generated Traffic AM Peak Period
In Out
Location TEP TC SUE W SUE E TEP TC SUE W SUE E
Norwich 57 38 31 63 41 27 23 45
Watton 33 22 18 36 23 16 13 26
King's Lynn 49 33 27 54 35 23 20 39
Brandon 72 48 40 80 52 35 29 58
Cambridge 29 19 16 32 21 14 12 23
Bury St Edmunds 23 16 13 26 17 11 9 19
Ixworth 31 20 17 34 22 15 12 24
Diss 24 16 13 27 17 12 10 19
TOTAL 317 212 176 353 228 152 127 253
Table 6.14: Distribution of Employment Generated Traffic PM Peak Period
In Out
Location TEP TC SUE W SUE E TEP TC SUE W SUE E
Norwich 41 27 23 45 57 38 31 63
Watton 23 16 13 26 33 22 18 36
King's Lynn 35 23 20 39 49 33 27 54
Brandon 52 35 29 58 72 48 40 80
Cambridge 21 14 12 23 29 19 16 32
Bury St Edmunds 17 11 9 19 23 16 13 26
Ixworth 22 15 12 24 31 20 17 34
Diss 17 12 10 19 24 16 13 27
TOTAL 228 152 127 253 317 212 176 353
Traffic flows generated by the new employment are shown in Figures 6.3 and 6.4 below.
233902/BSE/NOR/5-1/C 21 February 2011
20Transport Plan for Thetford
Highway Interventions
Figure 6.3: External Trips Generated by Employment Sites within Thetford AM Peak Hour – Turning Movement Diagram showing Arrivals and Departures to SUE, TEP and Town
233902/BSE/NOR/5-1/C 21 February 2011
21Transport Plan for Thetford
Highway Interventions
Figure 6.4: External Trips Generated by Employment Sites within Thetford PM Peak Hour – Turning Movement Diagram showing Arrivals and Departures to SUE, TEP and Town
233902/BSE/NOR/5-1/C 21 February 2011
22Transport Plan for Thetford
Highway Interventions
6.5 2026 Traffic Distribution
Growth factors have been applied to the 2009 baseline survey data to derive 2026 baseline traffic
movements. The calculation of these factors is provided within Section 4 and detailed in Figure 6.5.
Figure 6.5: 2026 Peak Hour Growth Factor Calculations
Traffic that is forecast to be generated by both the residential and employment sites within the SUE have
been added to the growthed baseline flows and the subsequent turning movement diagrams are provided
in Figures 6.6 and 6.7 for both the AM and PM peak hours in 2026.
A preliminary Link Capacity Appraisal has been undertaken for both the 2026 background traffic with
Development Scenario and the 2026 background traffic with development and soft measures Scenario
based on the maximum hourly capacity at each link end as detailed within section 5 and in Table 5.1.
Figures 6.6 and 6.7 summarise the results of the link capacity assessments for the 2026 Base with
Development Scenario.
The link capacities on the plans have been categorised as follows;
Green: 0 – 0.999 (within capacity);
Yellow: 1.000 – 1.099 (within the 10% margin noted in TA79/99); and
Red: 1.100 and greater (over capacity)
In every case ratios have been provided at both ends of the selected links and the ‘inbound’ ratio is shown
above ‘outbound’.
These numbers are assessed in section 7.3, below.
233902/BSE/NOR/5-1/C 21 February 2011
23Transport Plan for Thetford
Highway Interventions
6.5.1 HGV Traffic Growth Assumptions
The ARCADY, LINSIG and PICADY models in this report have been based on the existing HGV ratios for
each turning movement, however, the VISSIM model is based on an HGV and non HGV split. It is
considered that the revisions in HGV growth undertaken for the purpose of the VISSIM model would only
result in very minimal changes, which would not impact on the type and scale of interventions
recommended through the operational capacity assessment work undertaken within this study.
233902/BSE/NOR/5-1/C 21 February 2011
24Transport Plan for Thetford
Highway Interventions
Figure 6.6: Turning Movement Diagram 2026 AM Peak Hour Baseline with SUE Development Generated Traffic Flows (All Trip Purposes) with Link Capacity
233902/BSE/NOR/5-1/C 21 February 2011
25Transport Plan for Thetford
Highway Interventions
Figure 6.7: Turning Movement Diagram 2026 PM Peak Hour Baseline with SUE Development Generated Traffic Flows (All Trip Purposes) with Link Capacity
233902/BSE/NOR/5-1/C 21 February 2011
26Transport Plan for Thetford
Highway Interventions
7. Do-Something Scenario
7.1 Introduction
This is the scenario that would arise if the planned growth of new homes and associated employment
development were to occur but assuming a lower level of trip generation due to the implementation of
Smarter Choices. As with the Do-Minimum (no Smarter Choices scenario) no improvements are assumed
to the transport network to mitigate the impact of the additional journeys. This scenario also includes the
impact of general growth in vehicle trips brought about by growth outside Thetford up to 2026.
The Highways Agency has stated that the proposed TAAP and SUE development should cause ‘nil
detriment’ on the A11 junctions, ie after interventions the A11 must be no worse than if the TAAP had not
been adopted.
To accommodate the level of growth outlined in the TAAP, a number of potential improvements and
interventions, both soft measures and physical changes have been developed and tested in order to
reduce the impact of development generated traffic on the local and strategic highway network. These
options are discussed within this Section.
7.2 Reduced Containment within the SUE and Soft Measures
A number of ‘soft measures’ are proposed in Mott MacDonald report ‘Smarter Choices’, to reduce the
number of car trips generated by the TAAP.
The following have been discussed and agreed with Norfolk County Council and analysed as part of the
operational capacity assessments that have been undertaken;
Sustainable options which are envisaged to lead to a reduction in SUE residential generated driver trips
for journeys to work, by 10% for external trips and a reduction of 25% for internal trips eg mode shift to
rail and bus for trips to Norwich and Cambridge and some reduction in car trips based on potential
improvements to the cycle network; and
A reduction in external journeys to work to Thetford from 40% (2,000 trips) to 30% (1,500 trips) to reflect
increased containment within Thetford. In addition, the trip rates for external journeys to work to
Thetford have been reduced by 10% to reflect the proposed improvements to public transport services.
Traffic that is forecast to be generated by both the residential and employment sites within the SUE, with
soft measure reductions has been added to the growthed baseline flows and the subsequent turning
movement diagrams are provided in Figures 7.1 and 7.2 for both the AM and PM peak hours in 2026.
These also show the ratio of link traffic to capacity in both of the peak hours. A summary of movements is
provided in Appendix D.
233902/BSE/NOR/5-1/C 21 February 2011
27You can also read
