a. model framework and forecasting methodology

YEOVIL TRANSPORT STRATEGY REVIEW Final Report

5025094.101 Yeovil TSR 147 YeovilTSR_StrategyAppv0.doc

A. Model Framework and Forecasting Methodology

MODEL COMPONENTS

A.1 The modelling framework was developed using the Yeovil Traffic Model developed jointly for SCC and the Highways Agency (HA). The model base is a 2002 neutral month.

A.2 The model network includes all the classified roads and local roads within Yeovil and the surrounding area. The network also includes the A303 between South Cadbury and South Petherton.

A.3 The Yeovil Traffic Model was developed in SATURN and was designed to represent highway travel (car, light goods vehicles and heavy goods vehicles) within and through the study area for the AM (08:00–09:00) and PM (17:00–18:00) peak hours. Buses were included as pre-loaded flow along fixed routes, though no bus demand or mode shift was modelled.

A.4 Each of the peak hour models has a linked pre-peak hour model whose purpose is to replicate congestion at the beginning of the modelled peak hour, thus providing a more realistic representation of congestion and delay. The majority of the model is included in the simulation area, thus modelling fully junction delay. Link speed/flow effects are captured through individual speed/flow curves allocated to each link.

A.5 The Yeovil Traffic Model has also been developed further to include a SATCHMO based park & ride (P&R) sub-model to allow the assessment of P&R proposals in Yeovil. This is discussed in a later section in this report.

FORECASTING

A.6 The YTSR assumes a 2011 strategy year. Forecasts were prepared using data from the TEMPRO 4.2.3 database adjusted to include local planning data.

A.7 The TEMPRO database is linked to the forecasts of traffic growth by mode provided by the National Trip End Model (NTEM). TEMPRO comprises a series of forecasts relating to population, households, workforce and employment at a district and sub-district level.

GROWTH IN TRAVEL DEMAND

A.8 The growth factors to take the demand matrices from 2002 to 2011 were based on TEMPRO policy based travel demand growth forecasts and these were adjusted by applying the appropriate fuel price and income factors shown in Table A.1. These factors were at TEMPRO sector or district level within Somerset and county level outside Somerset. Trips at external cordon points in the model were factored by National Road Traffic Forecasts (NRTF) all-vehicle factors to reflect the lack of knowledge on the trip ends of trips at these cordon points.



Table A.1 - Fuel Price and Income Adjustment Factors (relative to 2002)

2005 2011 2016 2021

Income 1.009 1.025 1.042 1.059

Fuel Prices 1.037 1.075 1.098 1.105

Source: TEMPRO 4.2.3.

A.9 Within South Somerset trip end growth factors were not applied directly to the demand matrices. In zones where it was known that new developments (both residential and employment) were proposed forecast trip ends were estimated based on development area, proposed land use and intensity of development.

A.10 New developments were identified in discussions with both SCC and SSDC. These included SSDC Local Plan allocations, those identified in modifications to the Local Plan and some town centre ‘windfall’ sites where SSDC anticipate development to occur before the 2011 strategy year.

A.11 Table A.2 details the housing and employment planning assumptions used in the YTSR. The locations of these developments can be seen in Figures A.1 and A.2.

Table A.2 - Major Developments, Housing and Employment

Ref Location Quantity Policy Reference Notes

Housing - Sites with Permission or Under Construction (dwellings)

H1 Abbey Manor Park 133

H2 Dorchester Road 11

H3 North of Westlands 145

H4 Clarence Street 23

H5 North of Preston Road 11

H6 Salthouse Lane 17

H7 North of Sparrow Road 0

H8 Lufton Way 49

H9 Stoke sub Hamdon 19

H25 Petters Way 14 New permission - apartments

H26 Somerset Inn, Preston Rd 12 New permission - flats

Housing – Local Plan Allocation (dwellings)

H11 West of Larkhill Road 55 HG/YEOV/# Policy Reference HG2 refers to 55 dwellings

H12 Jewson's Yard 17 HG/YEOV/? Policy Reference HG2 refers to 17 dwellings

H13 Bucklers Mead 15 HG/YEOV/*

H14 Gas Works Martock 14 HG/MART/*

H15 South Petherton 30 HG/SOPE/1

H16 South Petherton 51 HG/SOPE/2

H17 Lufton 616 KS/BRYM/1 Significant increase in site area and number of dwellings

H18 Thorne Lane 580 KS/YEWI/2 Policy Reference HG2 refers to 580 during the plan period (670 total)

H19 Lyde Road 717 KS/YEWI/1 Small reduction in dwellings

H20 Milborne Port 18 HG/MIPO/1



Ref Location Quantity Policy Reference Notes

H21 Crewkerne Key Site 438 KS/CREW/1 Now allocated for all to be complete in plan period

H22 Crewkerne Charlton Close 19 HG/CREW/3

H23 Crewkerne Maiden Beech 110 HG/CREW/4

H24 Misterton 0 HG/MIST/2 Proposed to be deleted

H10 Yeo Paul Martock 110 Moved from above as now to be allocation via Plan Modification

H27 Foundry House/Mill Lane

H29 Cattle Market Site

H30 South Street Car Park

H31 Netwton Street Car Park

H32 Central Road Car Park

H33 Queensbury Place Car Park

Primary Schools (pupils)

S1 Thorne Lane 420 pupils KS/YEWI/2

S2 Lyde Road 210 pupils KS/YEWI/1

Employment – Sites with Permission or Under Construction (hectares)

E1 Mead Avenue 0.79

E2 East of Lufton Way (1) 0.72

E3 North of Copse Lane (1) 1

E4 North of Copse Lane (2) 0.77

E5 Watercombe Park 1.1

E6 East of Lufton Way (2) 3.7

E7 Summerhouse Lane 0.5

E8 Artillery Road 5

Employment - Local Plan Allocation (hectares)

E9 South of Airfield 4.8 ME/YEOV/3 B1,B2 & B8

E10 Watercombe Park 2.88 ME/YEOV/5 B1,B2 & B8

E11 Lufton 4.5 KS/BRYM/1 B1,B2 & B8

E12 Bower Hinton 1.8 ME/MART/2

E13 Crewkerne Key Site 10.5 KS/CREW/1

E14 Crewkerne Cropmead 0.8 ME/CREW/6

E15 Higher Farm Trading Estate

1.5 ME/YEOV/* B1,B2 & B8 (to the rear of Asda & serviced via Bluebell Rd Roundabout)

E16 Land off Bunford Lane 15.0 ME/WECO/* B1 (off A3088 Western Relief Road)

E17 Land off Bunford Lane 9.0 ME/WECO/* B1,B2 & B8 (off A3088 Western Relief Road)

E18 Foundry House/Mill Lane

E19 Vincents Site Retail

E20 Cattle Market Site

E21 Box Factory Site

Source: SCC/SSDC

TRIP RATES

A.12 Forecast trip ends associated with the major developments were estimated based on land area, proposed land use, and appropriate trip rates. The trip rates were estimated for each land use type from observed data held in the TRICS trip rate



database (version 4.6). Trip-rates for each time period were extracted for the relevant sites and the average trip-rates were then used with central traffic growth obtained from TEMPRO 4.2.3. The trip rates are shown in Table A.3.

Table A.3 - Assumed Development Trip Rates

Trip Rates (Average)

AM Peak PM Peak

Land-Use

Class In Out In Out

Mixed housing (per household) C3 0.12 0.50 0.42 0.20

Office (per 100m2 of GFA) B1 1.82 0.24 0.19 1.32

Industrial estate (per 100m2 of GFA)

B2 1.06 0.20 0.20 0.92

Distribution (per 100m2 of GFA) B8 0.17 0.08 0.10 0.17

Primary School D1 0.25 0.21 0.02 0.02

Retail A1 1.3 0.67 1.6 1.84

Source: TRICS v4.6 Notes: 1. Proposed trip rates are based on TRICS (version 4.6) data. 2. Residential trip-rates are per household of development, all others are per 100 sq m Gross Floor Area (GFA) 3. Trip rates are all vehicles per hour, including HGVs 4. All TRICS data is for weekdays from 1995 onwards except for Distribution which is from 1991 onwards. 5. Also all TRICS data is for England (excluding Greater London) except for ‘Office’ which includes Wales and Scotland and ‘Distribution’ which includes all data.

A.13 The numbers of light vehicle trips forecast in the AM peak hour for each of the new developments are shown below in Table A4. Similarly, Table A.5 shows the forecast trips ends for new development zones in the PM peak hour.

Table A.4 - Forecast light vehicle trips generated by new developments - AM Peak

Trips Ref Housing location

In Out

Housing – Sites with permission or under construction H1 Abbey Manor Park 18 73 H2 Dorchester Road 1 6 H3 North of Westlands 20 80 H4 Clarence Street 3 13 H5 North of Preston Road 1 6 H6 Salthouse Lane 2 9 H7 North of Sparrow Road 0 0 H8 Lufton Way 6 27 H9 Stoke sub Hamdon 3 10

H25 Petters Way 2 8 H26 Somerset Inn, Preston Road 2 7

Housing – Local Plan Allocation 10

H11 West of Larkhill Road 7 30 H12 Jewson’s Yard 2 9




In Out

H13 Bucklers Mead 2 8 H14 Gas Works Martock 1 8

H15/161 South Petherton 11 45 H17 Lufton 83 341 H18 Thorne Lane 77 320 H19 Lyde Road 95 395 H27 Foundry House/Mill Lane 1 10 H29 Cattle Market Site 3 25 H30 South Street Car Park 1 3 H31 Newton Street Car Park 1 6 H32 Central Road Car Park 1 4 H33 Queensbury Place Car Park 1 6

Soling Factory 20 83 Primary School (pupils) Primary School (pupils) S1 Thorne Lane 116 97

S2 Lyde Road 58 49 Employment – sites with permission or under construction (hectares) Employment – sites with permission or under construction (hectares) E1 Mead Avenue 25 5

E2 East of Lufton Way (1) 38 6 E3 North of Copse Lane (1) 37 7 E4 North of Copse Lane (2) 28 5 E5 Watercombe Park 35 7 E6 East of Lufton Way (2) 39 21 E7 Summerhouse Lane 50 7 E8 Artillery Road 159 30

Employment – Local Plan Allocation (hectares) Employment – Local Plan Allocation (hectares) E9 South of Airfield 222 33

E10 Watercombe Park 133 20 E11 Lufton 208 31

E16/17 Land off Bunford Lane 2317 298 E18 Foundry House/Mill Lane 34 10 E19 Vincents Site 173 89

Cattle Market Site 86 25 South Street Car Park 10 4 Newton Street C/Park 8 3 Central Street C/P 19 7 Queensway Place C/P 150 20 Box Factory Site 68 33

Table A.5 - Forecast light vehicle trips generated by new developments - PM Peak


In Out

Housing – Sites with permission or under construction H1 Abbey Manor Park 62 29 H2 Dorchester Road 5 2 H3 North of Westlands 67 32 H4 Clarence Street 11 5 H5 North of Preston Road 5 2 H6 Salthouse Lane 8 4 H7 North of Sparrow Road 0 0




In Out

H8 Lufton Way 23 11 H9 Stoke sub Hamdon 9 4

H25 Petters Way 6 3 H26 Somerset Inn, Preston Road 6 3

Housing – Local Plan Allocation H11 West of Larkhill Road 25 12 H12 Jewson’s Yard 8 4 H13 Bucklers Mead 7 3 H14 Gas Works Martock 6 3

H15/161 South Petherton 38 18 H17 Lufton 203 96 H18 Thorne Lane 269 121 H19 Lyde Road 332 158 H27 Foundry House/Mill Lane 5 2 H29 Cattle Market Site 9 4 H30 South Street Car Park 2 1 H31 Newton Street Car Park 5 2 H32 Central Road Car Park 4 2 H33 Queensbury Place Car Park 5 2

Soling Factory 69 33 Primary School (pupils)

S1 Thorne Lane 9 9 S2 Lyde Road 4 4

Employment – sites with permission or under construction (hectares) E1 Mead Avenue 4 18 E2 East of Lufton Way (1) 5 26 E3 North of Copse Lane (1) 5 18 E4 North of Copse Lane (2) 4 14 E5 Watercombe Park 6 26 E6 East of Lufton Way (2) 20 87 E7 Summerhouse Lane 5 36 E8 Artillery Road 27 118

Employment – Local Plan Allocation (hectares) E9 South of Airfield 27 145

E10 Watercombe Park 16 87 E11 Lufton 25 136

E16/17 Land off Bunford Lane 280 1846 E18 FoundryHouse/Mill Lane 20 35 E19 Vincents Site 212 244

Cattle Market Site 49 87 South Street Car Park 8 12 Newton Street C/P 6 9 Central Street C/P 15 22 Queensway Place C/P 16 109 Box Factory Site 77 92



TRIP DISTRIBUTION

A.14 Forecast light vehicle trips to and from the development sites in the study area in the AM and PM peak hours were distributed to origins and destinations respectively on the basis of a function derived from the calibration of 2002 trips and costs:

F(c) = e-ßCij

A.15 Where:

♦ Cij = cost between zone i and development j; and

♦ ß = constant based on a calibrated comparison of base year trips and costs (0.11 and 0.19 for the AM and PM peak respectively).

A.16 The matrix was then Furnessed to existing trip ends factored by TEMPRO 4.2.3 and development trip ends.

A.17 The cost matrix (Cij) was extracted from an unloaded 2011 forecast network and was subsequently adjusted to remove short and long trips (shorter than 3 minutes and greater than 90 minutes respectively).

A.18 The major developments within the Yeovil area were coded explicitly in the model to provide a realistic distribution of growth. Overall growth over the rest of the matrix was controlled to TEMPRO 4.2.3 expectations. The TEMPRO factors were adjusted to net out the trips associated with the major developments, therefore avoiding the possible double counting of such trips, and then applied as background growth to non-development zones using a Furness procedure.

A.19 The forecast heavy goods vehicle matrices were prepared by factoring the base year trip matrices by National Road Traffic Forecast (NRTF 1997) growth factors.

TRIP SUPPRESSION AND MODE DIVERSION

A.20 The TEMPRO growth factors represent growth in overall travel demand but take no account of the level of available capacity in the transport system. At peak times, capacity constraints on the highway network will be such that the full level of growth implied by TEMPRO gives levels of delay and congestion, which, in practice, are likely to lead to a change in travel behaviour. Such a change my take a number of forms:

♦ Re-time their journey and travel outside the peak

♦ Not make the trip at all, or make a different trip

♦ Choose an alternative mode; or

♦ Use an alternative route.

A.21 These effects have been predicted in the reference case modelling (and for all subsequent future year modelling) by representing trip suppression (through the application of a demand elasticity relative to change of cost) and modal shift (through a logit-based mode choice model). Change in route choice was forecast within the highway assignment procedure.



A.22 Unconstrained demand forecasts derived using TEMPRO factors were first of all assigned to the highway network. A simple elastic assignment was then applied to estimate levels of suppressed demand, thereby taking into account the likely response of motorists to large increases in travel time as a result of congestion. This process assumes as elasticity with low modal competition in line with DfT’s guidance in induced traffic, as contained in the Design Manual for Roads and Bridges. The resulting highway matrix represented the reference case demand.

A.23 The forecast highway modelling procedure is summarised in the flow chart diagram shown in Figure A.3.

FORECAST YEAR HIGHWAY SCHEMES

A.24 The reference case network has been based on the 2002 validated base year network. This network has been modified to include all committed highway schemes (i.e. those set out in the Local Transport Plan and Local Structure Plan) expected to be in place by 2011, the strategy year. It also includes other schemes that though not committed are expected to be constructed by 2011. SCC and SSDC have advised on these schemes.

A.25 The forecast highway schemes for 2011 are listed below:

♦ Lufton/Thorne Lane – New roundabout on New Road and the enlargement of the Preston Road Roundabout and the provision of a mini roundabout at Preston Road/Lufton Road Junction;

♦ Lyde Road – New distributor road;

♦ Thorne Lane – New distributor road between Brimsmore and Thorne Lane/Western Avenue;

A.26 The location of these schemes can be seen in Figure A.4.

A.27 The reference case network also contains measures which have been implemented since the base year (2002). This includes closing Silver Street/High Street to all private vehicles (but leaving open for taxis and buses) and the 20 mph zone along and around St Michael’s Avenue.

A.28 The model network also contains two other modifications which it was felt would be constructed by 2011:

♦ Traffic calming along the existing Thorne Lane to encourage traffic to use the new distributor road; and

♦ A modest increase to the capacity of the roundabouts at the junctions of A3038 Watercombe Road/A3088 Lysander Road and A3088Western Relief Road/Bunford Lane/Cartgate Link. This was designed to ease delay at these junctions that was attributable to the large development sited adjacent to the A3088 at Bunford. The improvements consisted of widening two arms of each roundabout from two to three lanes. These schemes should not be regarded as the definitive level of works needed on the highway network for this development but were a means of creating a realistic reference case assignment in the YTSR traffic model for this study.



A.29 In all forecast year runs, both reference case and strategy, the traffic signal timings were optimised to reduce delay at junctions. This was a realistic assumption as in reality signal timings would be adjusted by the highway authority or would be responsive to traffic flows.



APPENDIX B

Forecast Reference Case Traffic Conditions

a. model framework and forecasting methodology

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