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Capacity Assessment for Elton Interchange



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Capacity Assessment for Elton Interchange

An assessment has been undertaken for the existing layout and the mitigation layout committed as part of the Allens West development. Fairhurst’s also proposed further improvements so that the Urlay Nook development trips result in no detrimental effect on the operation of the roundabout – however the junction still operates above capacity during the morning peak. Furthermore, these assessments were based on the incorrect trip generation.

The proposed mitigation works are summarised in Table 3 below.

Table 153 Elton interchange improvements

Arm

Committed improvement as part of the Allens West development

Proposed improvement as part of Urlay Nook development

Northern Dumbell:

Durham Lane

Widen approach flare to include a short second lane

Increase approach flare by 3m

Darlington Road

Widen approach flare to include a short second lane

Increase approach flare by 2m

Southern Dumbell:

Durham Lane

Widen approach flare to include a short second lane

Increase approach flare by 3m

As the assessments were based on incorrect trip rates, it would be prudent to redo these to ensure that the proposed mitigation is still appropriate. In addition, prior to determination of the application, the proposed works would need to be subject to an independent road safety audit. However, as the dumbbell roundabout junction is not part of the HA network this would be a matter for the local authority.

      1. Merge / Diverge Assessment


              1. Merge / diverge assessments have been undertaken at the Elton interchange on the eastbound merge and westbound diverge. The committed development flows were not included in the assessment however it is not thought this would drastically alter the conclusion made in the TA. The results show that the addition of the development trips does not change the merge/diverge category and therefore no mitigation work is required.
      2. TRAVEL PLAN


A Framework Travel Plan has been prepared to accompany the TA, which contains an accessibility assessment, multi-modal trip generation and a small number of potential measures. We would suggest that there is no reason why a full Travel Plan cannot be submitted at this stage and approved prior to determination of this application. This will demonstrate a firmer commitment to the promotion of sustainable modes of transport.
      1. SUMMARY


Transport Assessment:

There are many errors throughout the Transport Assessment, however, it has been determined that this development is unlikely to have a detrimental effect on the SRN. Therefore please find attached a TR110 direction offering no objections to the above named development proposals.

I trust that my comments are clear, however, if you require anything further then please do not hesitate to contact me.

The Head of Technical Services (Stockton Borough Council)

General Summary

The Head of Technical Services has reviewed the information submitted by the applicant and has no objection to the development, subject the comments outlined in the report below.

Highway Comments

All comments are made taking into account that all matters for this development would be reserved, with the exception of the access and main spine road.


A number of additional sources of information have been provided since the application was initially submitted and this report summarises the findings of the review of all information submitted including:

  • Review of development layout proposals based on submitted plans.

  • Consideration of the Transport Assessment (TA) and Travel Plan submitted with the Planning application;

  • Review of additional transport modelling of the A67 / Durham Lane / Tesco roundabout undertaken by the applicant; and

  • The results of the transport modelling commissioned by Technical Services to assess the wider impact of this development and others locally on the highway network.

Development Layout

One vehicular access to the development is proposed. The access location is suitably located between the two existing access points to the residential development opposite (Grassholme Way). No obstructions should be placed within the visibility splay of the access to ensure vehicles could emerge from the site safely. An analysis of the operation of the junction shows that the site access and the A67 / Urlay Nook Road roundabout could accommodate the development traffic with both junctions operating with plentiful spare capacity in future years.

The internal layout should be designed in accordance with Manual for Streets guidance. The route through the site should be a minimum of 4.8m wide (this could be reduced on the minor access routes) and a 2m wide footway should be provided on both sides of the carriageway. The applicant would need to enter into a Section 38 (S38) Agreement for the highway and footpaths which are to become highway maintainable at the public expense.

The previous layout proposed a POS to be delivered as a linear corridor following the line of the corridor of the A67. This proposed location would have brought the active ball games ('kick about' area) in close proximity (12 metres) to the carriageway of the A67. It was subsequently considered that there would be a risk to safety (both to the children playing on the 'kick about' area and to drivers from miss kicked balls entering the busy highway) and the applicant was asked to amend the proposal. A revised layout plan has been provided (81165-G7-SI-102-F) and the revised proposal is acceptable (see Open Space comments for more details).
An existing Public Rights of Way (PRoW) runs through the proposed site and is incorporated within the open space to the south of the proposed residential properties. As the area is to be developed for residential development it is necessary to improve the condition of the path to provide an 'all weather path'. As the footway is within the area of open space the applicant has asked if this could be upgraded as part of the development construction works rather than the improvements being undertaken by the Highway Authority (at the developers' expense). This is acceptable subject to the works being implemented to the required specifications and being approved by the Council's Right of Way officer. It should be noted that granting of planning permission does not entitle the developer to obstruct the Public Right of Way and permission would need to be granted to temporarily close the route during improvement works. Enforcement action may be taken against any person who obstructs or damages a Public Right of Way.

Additional pedestrian and cycle links should be incorporated into the development layout to provide attractive pedestrian and cycle links which reduce the need for pedestrians to divert off their desire line. Community facilities are located to the south-east of the development and therefore the layout should consider how it could reduce pedestrian journey lengths between the community facilities and the site to encourage pedestrian trips and discourage short distance car trips. An additional crossing point (dropped kerbs and tactile paving) on Urlay Nook Road would improve connections to the south-east and should be provided as part of a Section 278 Agreement with the Highway Authority. A crossing located between the proposed vehicular access to this development and Grassholme Way would strengthen pedestrian connections between the site and the surrounding area (see Travel Plan comments). The applicant is also asked to contribute towards cycleway improvements as outlined in the Travel Plan comments (detailed in later section of report).

The application is in outline; however details of car parking are indicated. Car parking should be provided for each dwelling in accordance with SBC parking standards. A total of 395 car parking spaces are proposed but it is not specified (or clear from the site layout plan) how these spaces would be delivered. Parking provision should be as follows:
Table 1: Parking Provision

Number of Bedrooms Standard Proposed Dwellings Spaces

4 bed 3 spaces per dwelling 79 237

3 bed 2 spaces per dwelling 61 122

2 bed 2 spaces per dwelling 19 38

Total 397

The standards require an additional 2 spaces compared to the 395 proposed - the applicant should confirm details of the proposed parking provision as part of any future reserved matters application.
Each in-curtilage parking space should be 6 metres in length to ensure that parked cars do not overhang the footway. In accordance with the parking standards, a garage can only be counted as a parking space if it meets the minimum internal dimensions of 6m x 3m.

Transport Assessment (TA)

Trip rates used in the TA have been derived from traffic surveys at the residential estate opposite and this methodology is considered to be acceptable. However, the calculation of trip forecasts, based on the trip rates, presented in the original TA was incorrect. The trip rates would result in 137 two-way trips in the AM peak hour and 129 two-way trips in the PM peak hour generated by the development (compared to 128 and 192 outlined in the TA report). Trips in the AM peak hour are therefore under-estimated in the TA assessment and trips in the PM peak hour are over-estimated.

The TA explains that the traffic distribution forecast has been based on journey to work data from the 2001 Census and the Highways Agency PENELOPE distribution which looks at the wider strategic network distribution. This was considered to be acceptable during pre-application discussions between the Council, Highways Agency and the applicant.
However, it was raised with the applicant that just using Census journey to work data misses the opportunity to use the actual traffic data collected from the residential estate opposite (Grassholme Way residential development). Traffic surveys at the two access points to the Grassholme residential development were conducted in November 2011 and the information derived from these surveys should have been given due consideration and informed the overall assessment. The traffic counts from these surveys have informed the development trip rates and therefore they should also have been reviewed to inform the development traffic assignment. The traffic surveys from the Grassholme Way development show the traffic distribution of vehicles accessing the estate during the peak hours as shown in Table 2.

Table 2: Traffic Distribution based on November 2011 Traffic Surveys at Grassholme Way

Total Inbound Distribution Total Outbound Distribution

South North South North

AM Peak (07:45 - 08:45) 16 15 (94%) 1 (6%) 92 91 (99%) 1 (1%)

PM Peak (16:45 - 17:45) 61 56 (92%) 5 (8%) 41 41 (100%) 0 (0%)

The traffic distribution from the surveys at Grassholme Way (Table 2) clearly show that in the AM and PM peak hour the majority of trips travel south towards the A67 / Urlay Nook roundabout. The TA however, using the wider network strategic distributions, proposes the distributions at the development site access as outlined in Table 3.

Table 3: Traffic Distribution (to / from the site access) applied in TA

Inbound Outbound

South North South North

Daily 87% 13% 87% 13%


The traffic distribution applied in the TA shows a greater proportion of traffic travelling to/from the north on the A67 and avoiding the A67 / Urlay Nook Road roundabout. This distribution could under-estimate the forecast number of trips travelling towards Eaglescliffe / Yarm and is less robust than using the distribution assignment from the traffic counts.
The observed traffic assignment at the A67 / Urlay Nook Road roundabout (from SBC traffic surveys in January 2012, supplied to inform the TA) is shown for the AM and PM peak period in Table 4.
Table 4: Traffic Assignment based on Traffic Surveys at A67 /Urlay Nook Road Roundabout

From Urlay Nook Rd North From A67 west From A67 east

East West North East North West

AM 94% 6% 1% 99% 14% 86%

PM 93% 7% 1% 99% 26% 74%
Table 5 shows the development traffic distribution at the roundabout that has been applied in the TA.
Table 5: Traffic Distribution for Development Traffic at the Roundabout applied in TA

From Urlay Nook Rd North From A67 west From A67 east

East West North East North West

Daily 72% 15% 15% 0% 72% 0%

The key assumption that would affect the wider network is the proportion of traffic that comes to / from the east and would travel through the A67 / Tesco roundabout. The observed data shows that currently 94 / 93% (AM and PM peak periods respectively) of traffic approaching the roundabout from Urlay Nook Road travels east towards the Tesco roundabout. The TA assumes that only 72% of development traffic would make this trip. This is a result of the distributions at the access being based on Census data rather than observed data and assuming that a greater proportion travels north and never enters the Urlay Nook Road / A67 roundabout. The actual data shows that whilst trips may be travelling to final destinations to the north, linked trips are being made to locations to the south (e.g. schools).

At the A67 / Durham Lane / Tesco roundabout the traffic assignment in the TA shows that from the A67, development traffic is only forecast to travel to / from the north on Durham Lane (57%) and to / from the south (15%) on the A67. The same distribution proportions are applied in both the AM and PM periods. The distribution of trips based on the SBC traffic surveys carried out in January 2012 (and supplied to inform the TA) are shown in Table 6.

Table 6: Traffic Distribution based Traffic Surveys at the A67 /Durham Lane Roundabout



From

To




Durham Lane (north)

A67 (south)

A67 / Urlay Nook Road

AM Period










A67 / Urlay Nook Road

26%

65%




Durham Lane (north)







14%

A67 (south)






45%


PM Period










A67 / Urlay Nook Road

24%

64%




Durham Lane (north)







22%

A67 (south)







42%

The data in Table 6 further exemplifies that the assumption applied in the TA (that the majority of development traffic that travels through this junction would travel to / from Durham Lane to the north) is unrealistic. Current distributions show that 65 / 64% (AM and PM peak periods respectively) travel to the south towards Eaglescliffe and Yarm.

The results of the junction analysis in the TA at the A67 / Durham Lane / Tesco roundabout show that this junction currently experiences no issues in the base year with queues below 1 PCU (passenger car unit - units used in the model to represent vehicles) on each arm in the AM period and the highest RFC (ratio of flow to capacity) on the Durham Lane arm of 0.46 (RFC <1 is considered to be operating within capacity). This appears low for a junction which is generally known to be busy in the peak periods. In the future year scenarios, the RFC at the Durham Lane arm of the Tesco roundabout increases to 0.84 with the queue rising to 4.98 PCU's. Without this development (but with committed development), the queue is forecast to be 4.43 with an RFC of 0.82 in 2022. Therefore, it would appear that this proposed development does not significantly worsen the situation with committed developments accounting for the increase. However, given the concerns raised with the traffic distributions, the applicant was asked to undertake additional testing at this junction (see comments in 'Additional Modelling' section).

The distribution at the Durham Lane / A66 Elton interchange junction applied in the TA is based on Highways Agency data and the majority of traffic is assigned to the A66. This assignment is considered to be acceptable. The junction assessment however demonstrates that the interchange operates over-capacity in the future year, with and without the development. The applicant proposes measures to mitigate the impact but some arms of this junction would still operate over capacity, but this is attributed to the Allen's West development rather than this proposed development.
The proposed improvements to mitigate the impact of the traffic associated with this development are to increase flare widths at three of the roundabout approaches at Elton Interchange to increase capacity as follows (specified works):


  • Northern dumbbell

  • Durham Lane - increase approach flare by 3m

  • Darlington Road - increase approach flare by 2m

  • Southern dumbbell

  • Increase approach flare by 3m

It should be noted that these improvements build upon committed improvements as part of the Allen's West development. The Allen's West committed improvements include widening the Yarm Back Lane and Darlington Road approaches to the northern roundabout of the dumbbell arrangement and also the Durham Lane approach to the southern roundabout. These committed improvements would be undertaken as part of a S278 Agreement with the Highway Authority and were estimated (when the Allen's West application was being reviewed) to cost approximately £63,000.

It would not be practical to bring forward the mitigation measures associated with this development (the specified works) before the committed improvements for the Allen's West development were implemented - the improvements would benefit from being delivered in a coordinated approach. However, it is possible that this development may come forward before the Allen's West development. It is therefore suggested that if upon occupation of the 20th property of this development the applicant has not entered into a S278 Agreement for the coordinated highways works required at the junction, the applicant should provide a Section 106 (S106) for the specified works. The S106 contribution would be for the amount applicable for the specified works that would be delivered as part of a S278 Agreement with the Highway Authority for the coordinated improvements at the interchange.

The TA does not identify the impact of the development on Yarm High Street. The applicant was advised during pre-application discussions about the congestion and parking concerns at Yarm High Street. It was noted that any increase in traffic would be considered material and would require mitigation. This has not been covered in the TA but it is anticipated that some future residents of the proposed development would use the facilities in Yarm as it is the nearest local service centre.
As the impact on Yarm High Street has not been demonstrated in the TA, the ratio derived from the Allen's West development has been applied. Based on 160 dwellings, the development is forecast to generate demand for an additional 7 spaces close to Yarm High Street (0.046 spaces per dwelling). In line with other local developments the applicant is therefore required to provide these spaces in a fully operational long-stay public car park to serve Yarm High Street prior to occupation of the 10th dwelling. If the applicant cannot deliver this car park then an alternative financial contribution towards a Local Authority operated public car park to serve Yarm High Street could be provided (£64,166). Should this alternative financial contribution be provided then this public car park must be fully operational prior to the occupation of the 10th dwelling.

Travel Plan


The Framework Travel Plan suggests that the volume of cyclist trips is low - an ideal target for the Travel Plan would be to address this, especially given that there are several employment opportunities within the desirable 5km distance from the site (Tesco, Yarm High Street, Durham Lane Industrial Estate, Nifco, Preston Farm Industrial Estate). Stockton Town Centre and Teesdale are also approximately 8km from this development, which is not beyond the distance travelled by cyclists to and from work.

The Framework Travel Plan highlights several local amenities which are within the reasonable walking distance of 2km and local residents may choose to cycle to these locations, especially children to the local schools. To assist in the use of cycling as a sustainable mode of transport from this site there is scope for improvements to the highway network. A new cycle link should be provided between Lartington Way and Lingfield Drive. This would provide a connection from the promoted on-road cycle routes (SBC walking and cycling map) through the Grassholme Way (Hunters Green) estate and Lingfield Drive to nearby schools and other community facilities. The provision of this link should be included in the S106 agreement and all external works should be installed in accordance with the SBC Design Guide standards. This would provide not only a linkage to Tesco, Durham Lane shops and local schools but also to the cycleway network along Yarm Road.
Pedestrian crossing facilities should be improved on Urlay Nook Road. An additional crossing point (dropped kerbs and tactile paving) on Urlay Nook Road would improve connections to the south-east and should be provided as part of the S278 Agreement with the Highway Authority. These improvements should link to the cycleway.
A full Travel Plan should include targets for both an increase in sustainable modes of transport as well as a reduction in single occupancy car trips. Baseline data could be established from surveying the neighbouring residential estate. In addition to the Travel Plan incentive of cycle vouchers, bus travel vouchers should also be included in the welcome pack.




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