Cyngor Bro Morgannwg
Vale of Glamorgan Council

HG1 KS1 North West Barry (Weycock Cross)
RLDP Strategic Transport Assessments: BP14/BP14A/KS1 Draft TA (Asbri) Data-Based Objection

Ref: NWB_RLDP_JVN_008: RLDP public consulta on feedback (Data-Based Objection) on the
three key strategic transport assessments provided within the RLDP consulta on portal.
This RLDP consulta on feedback (objection letter) focuses on several key areas of contradiction
between the following documents with current transport planning policy (PPW, TAN18 etc).
 BP14 Strategic Transport Assessment – Stage 1 RLDP “Supporting Documents” (Nov 23)
 BP14A Strategic Transport Assessment – Stage 2 RLDP “Supporting Documents” (Dec 25)
 Dra Transport Assessment KS1 “Supporting Informa on” Persimmon Homes/Asbri transport
report (May 25)
This objection focuses specifically on the full strategic transport picture across all three STAs listed
above which were available for public review on the RLDP website, highlighting the following
concerns:
Weycock Cross conges on, the NWB signalised access, Active Travel provision, the quality and
reliability of traffic modelling inputs, and the absence of air-quality assessment data.
1. Severe and Quantified Congestion Impacts at Weycock Cross Roundabout (J16)
1.1 Baseline and Future Opera on (BP14/BP14A Findings):
BP14A shows that Weycock Cross is already opera ng close to capacity (even without accounting
for proposed strategic housing):
 Base RFC = 0.88 in both AM and PM peaks → “nearing practical capacity..”
When RLDP traffic, including the North West Barry (NWB) site, is added:
 RLDP RFC rises to 1.02 (AM) → over capacity = uncontrolled queueing at peak mes
 RLDP RFC rises to 0.97 (PM) → very close to failure
 Junc on delay doubles in both peaks, indica ng unstable opera on and significant
queuing..
1.2 Strategic Modelling Impacts (BP14A – SEWTM) and selective use of the TAN18 5% threshold:
SEWTM modelling (Technical Note 05) identifies significant percentage increases in total traffic
flows at Weycock Cross resulting from RLDP strategic growth:
 +7.2% AM
 +12.2% PM
These exceed the TAN18 threshold for requiring detailed modelling.
 The Dra Transport Assessment (TA) cri cises other TAs for not modelling arms with >5%
impact (quo ng TAN 18 Annex E), but then uses low percentage increases (1.3–3.4%) to
argue its own impact is negligible, despite RFCs >1.0 and acknowledged severe conges on.
 That is internally inconsistent with the focus of TAN 18, which explicitly notes that where
capacity is or nearly exceeded, even smaller increases are normally material
1.3 Conclusion – conges on modelling:
The Council’s own BP14A Stage 2 evidence directly contradicts the Dra Transport Assessment
(Persimmon Homes) and demonstrates that NWB materially worsens conges on in all directions
at the area’s most constrained junction.
The BP14/BP14A and Dra TA documents all downplay cumulative impact while acknowledging
severe future conges on
The Persimmon Dra TA accepts that with committed development, Weycock Cross will be
“extreme and unacceptable” and “over capacity”, yet still concludes the site’s impact is “marginal
and inconsequential”.
TAN 18 and PPW require consideration of cumulative impacts and whether the network is already
at or near capacity—small percentage increases can s ll be material where junctions are stressed
2. Impact of Proposed Signalised Access for NWB on the A4226
2.1 Proposed signalised junction
The Dra Transport Assessment (Persimmon Homes):
 Proposes a signalised junction
 Provides no network or corridor-wide analysis
 Provides no LinSig modelling
 Does not demonstrate compliance with the Welsh Government Roads Review (which limits
new capacity for general traffic)
2.2 Modelling Uncertainty and Omission (BP14A)
BP14A states that the interaction between the NWB access junction and Weycock Cross has not
been assessed within the TN06 modelling, because the applicant has not yet provided a full
junction design or modelling package. This omission introduces a significant gap in the cumulative
assessment.
2.3 Expected Operational Effects
A new signalised access on A4226 would:
 Introduce a new stopline on the corridor already under heavy peak pressure.
 Increase stop–start conditions, which worsens emissions (see Sec on 6).
 Alter flow profiles entering Weycock Cross, likely exacerbating queues on the A4226
eastbound and westbound arms.
Given that Weycock Cross is already over capacity, any upstream signalisation will further degrade
performance.
Conclusion: The NWB access junction has not been assessed cumulatively, and the omission likely
leads to material underestimation of network impacts.
3. Active Travel: Provision Limited, Non-Compliant, and Not Evidence-Based
3.1 BP14A Requirements
Mi ga on schemes must promote active travel in accordance with:
 Active Travel (Wales) Act 2013
 Wales Transport Strategy 2021
BP14A includes indicative active travel elements in mi ga on layouts (e.g., crossings, shared-use
links) but fails to provide any detail.
3.2 Weaknesses and Uncertainty Identified in BP14A
BP14A explicitly states that:
 Schemes are indicative only
 Subject to further design and land acquisition
 Dependent on funding and developer contributions
There is no guarantee that these facilities will be provided, or that they will be delivered before
occupation. In addition, the Weycock Cross site is in a location which is a steep uphill 30-40 minute
walk from the nearest train station, meaning any Ac ve Travel measures which are intended to
mi gate the site-generated traffic will have li le (if any) impact on commuting traffic increase.
3.3 Applicant TA Fails to Provide Active Travel ATAG-Compliant Evidence
The Persimmon Dra TA includes:
 No Active Travel Audit
 No ATAG compliance assessment
 No detailed geometric designs
 No crossing delay analysis, desire-line mapping, or route con nuity assessment
This makes it impossible to demonstrate compliance with Active Travel statutory du es.
4. Quality, Reliability and Limitations of Modelling Data
4.1 Poor quality base data used as the basis for the Dra Transport Assessment (Persimmon
Homes)
The Dra Transport Assessment (Persimmon Homes):
 Uses one day of turning counts (12 Sept 2023, 07:00–19:00)
 Uses pro-rata trip assignment
 No weekend or seasonal data
 TEMPro-only growth
 Does not include SEWTM routing
 Does not model cumulative RLDP-wide impacts
This does not satisfy modern Welsh transport appraisal requirements.
This results in a systema c underesmation of all movements at the junction.
4.2 Uncertain quality of base data used as the basis for the BP14/BP14A
BP14 and BP14A provide no details on how/when or where the base data for the reports was
gathered. This significantly reduces confidence in the outcomes and conclusions of those reports.
4.3 BP14A – Iden fied Limita ons in SEWTM Outputs
BP14A states:
 SEWTM has limited local validation in the Vale
 Some junctions are only par ally represented
 Traffic assignment may use minor links unrealistically
 The model includes no modal shift , demand suppression, or peak spreading
 Results should be interpreted with caution due to missing local constraints
These limitations lead to an under-prediction of congestion.
4.4 Data Sources Used in BP14A
 SEWTM 2022 base year data
 Supplementary traffic surveys for some junctions
 Factoring using TEMPro growth
However, key surveys for Weycock Cross came from other developments (e.g., Readers Way TA)
5. Cumulative Impacts and Risk of Infrastructure Lag
5.1 BP14A Mi ga on Costs
Mitigation measures are proposed at three junctions totals £5.2 million, with £3.8m to be funded
via developer S106 contributions. NWB is apportioned £410,835 at Weycock Cross.
5.2 Delivery Risks
BP14A states that:
 Mi ga on schemes are not yet designed,
 Claimed benefits from modelling data are not robust
 Not funded in full,
 Require land, design, statutory consulta on, and
 May not be delivered before development is occupied.
Note: Persimmon Homes, the North West Barry site developer, have a track record of failing to
deliver on promised S106 highway improvement measures at other sites, in some cases resulting in
legal enforcement ac on for years a er building work has been completed.
Therefore, there is a high risk of significant conges on long before mi ga on is operational.
6. Air Quality: No Reference to any Assessments Carried Out (Major Omission)
6.1 BP14, BP14A and Persimmon Dra TA
None of the three documents include any reference to an Air Quality Assessment (AQA).
6.2 Conflict with Policy Requirements
Under:
 PPW12 (Chapter 6)
 TAN 18
 Well-being of Future Generations Act
An AQA is required where development:
 Increases traffic,
 Worsens conges on,
 Increases stop–start condi ons,
 Produces emissions at sensi ve receptors.
BP14A shows:
 Weycock Cross → AM over-capacity, PM near-capacity
 J22 → +13.6% AM / +18.3% PM traffic increase
 Even with best-case mi ga on measures → stop–start condi ons remain
Thus, the absence of any AQA for the proposed Weycock Cross development is a fundamental
evidence gap which means the proposed Weycock Cross development is not suitable for
inclusion in the RLDP.
Overall Conclusion
Across all three RLDP Strategic Transport Assessment documents (BP14 Strategic Transport
Assessment - Stage 1 / BP14A Strategic Transport Assessment - Stage 2 / Persimmon Homes/Asbri
Dra Transport Assessment) the evidence demonstrates that:
 Weycock Cross will operate over capacity because of the cumulative development, even if
only North West Barry is considered. BP14A explicitly shows failure in the 2036 RLDP
scenario. The assessments use small percentage increases (1.3–3.4%) to downplay impact,
while ignoring that even small increases can p an already failing junction into severe
conges on.
 The North West Barry signalised access junction has not been assessed cumulatively,
leaving a material evidence gap, meaning impact on traffic conges on is likely to be even
worse than the modelling suggests.
 Ac ve travel provision in the plan is weak, indicative, and non-compliant with statutory
requirements, and does not take into account the location and topology of the site (long
uphill route from nearest train station, etc)
Traffic modelling data is incomplete, inadequately validated, and methodologically
inconsistent. The Persimmon Dra Traffic Assessment is based on a single day’s data in
September 2023. Likewise, BP14/BP14A provide no details on how or when data was
gathered.
 No air quality assessments are referenced in any of the three documents, despite clear
conges on and policy triggers. This directly contravenes PPW12 (Chapter 6), TAN 18 and
Well-being of Future Genera ons Act and this means the proposed Weycock Cross
development is not suitable for inclusion in the RLDP.
 There is a significant risk that traffic congestion mitgation will not be delivered before
occupation, leaving users with years of unacceptable conges on.
When all the above concerns are taken into account, this constitutes a robust, evidence-backed
basis for objection.