West Northamptonshire Council (WNC) commissioned City Science to assess the carbon impact of its forthcoming Local Transport Plan (LTP) to delivering its 2045 net zero ambition.
City Science was ideally placed to deliver this work. For more than a decade, we have been at the forefront of transport decarbonisation and carbon assessment, helping to shape the tools, guidance and techniques now used by authorities across the UK. Our assessment gave WNC a clear, data-led understanding of how far its LTP would take it towards net zero and where further action was needed.
Scope
The Department for Transport’s statutory LTP guidance includes the requirement for the Quantified Carbon Guidance (QCG) to be embedded within LTP development.
In line with this requirement, WNC needed a user carbon emissions assessment of the schemes and policies within its emerging LTP, including those related to its:
- Bus Service Improvement Plan (BSIP)
- Local Cycling and Walking Infrastructure Plans (LCWIPs) for Daventry, Brackley, Towcester and Northampton
- Electric Vehicle (EV) Strategy
The Carbon Assessment Playbook (CAP) is an online, free-to-access tool owned by the Sub-National Transport Body community. It has been designed to support the development of LTPs in line with the processes set out in the QCG. The scope of the commission was to use the CAP to assess the carbon impact of WNC’s emerging LTP. City Science played a leading role in developing the CAP and continues to host and maintain key components, giving us an in-depth understanding of its processes, capabilities and practical application. Choosing City Science gave WNC direct access to industry-leading practitioners who understand how to get the greatest value from the CAP.
City Science Response
Our approach combined detailed policy review, spatial analysis, carbon modelling and proactive recommendations, supported by close collaboration with WNC officers throughout.
Stage 1 – Transport Carbon Baselining: The CAP includes pre-loaded carbon baselines, which we used to give WNC a quantified understanding of current transport emissions and the forecast trajectory if no additional transport interventions were applied. We compared this with a credible emissions pathway aligned to WNC’s 2045 transport net zero ambition, identifying the emissions gap that LTP interventions would need to close. Our detailed knowledge of the CAP enabled us to provide this insight efficiently and cost-effectively.
Insight on current transport emissions sources, provided to WNC by City Science through use of the CAP.
Stage 2 – Policy Review: We undertook a detailed review of WNC’s Draft LTP, BSIP, draft LCWIPs and EV Strategy to identify the full range of proposed interventions. A focused workshop with WNC officers ensured the assessment captured all relevant schemes and reflected local delivery priorities from the outset.
Stage 3 – CAP Equivalency Mapping: Each WNC scheme was mapped to the most relevant of the CAP’s 29 intervention types, with the matches documented to create a transparent and defensible basis for the assessment. Having developed the modelling methods behind the CAP Policy Builder, City Science was best placed to select the most appropriate CAP intervention to represent each of WNC’s LTP schemes and policies.
Some of the 29 interventions currently available in the CAP
Stage 4 – Spatial Mapping: To input schemes and policies into the CAP, it is essential to understand their location. We used Cadence, our award-winning in-house geospatial software, to consolidate, analyse and catalogue the locations of WNC’s LTP policies and schemes efficiently. Cadence also enabled us to share online maps with WNC officers and stakeholders, supporting rapid validation of scheme locations and assumptions.
Cadence visualisation of place-types, supporting analysis of emissions generation and intervention suitability by location
Stage 5 – Carbon Impact Modelling: The schemes were grouped by intervention type and entered into the CAP Policy Builder, with build profiles, intensities and timescales informed by WNC officers. We modelled the LTP policy package against three ZEV uptake scenarios — Business as Usual, accelerated national uptake and a localised accelerated scenario reflecting West Northamptonshire’s characteristics — giving WNC a nuanced understanding of potential future emissions.
CAP Carbon modelling output on the combined emissions impact of WNC’s LTP schemes and policies
Stage 6 – Results & Recommendations: We consolidated the findings into a clear summary report, comparing each scenario against the Climate Change Committee pathway, breaking down reductions by vehicle type, journey purpose and trip length, and setting out the residual emissions gap. We also identified strategy gaps and recommended targeted actions to help WNC strengthen its decarbonisation pathway.
The Outcome
The assessment gave WNC a clear, quantified view of the carbon impact of its LTP and a robust baseline for measuring future progress. Under the high-uptake ZEV scenario, the analysis showed that the LTP policy package, combined with electrification, could reduce emissions by around 90% against the 2019 baseline by 2050, while also highlighting where residual emissions would remain.
City Science’s recommendations gave WNC a practical route to strengthen its strategy, including action on freight and through-trip emissions, consideration of demand-management measures, and the inclusion of whole-life infrastructure carbon. The project delivered more than a modelled output: it provided a clear, defensible evidence base and actionable recommendations to support better decisions.
For authorities developing transport strategies, the project demonstrates why City Science is the right partner for credible, evidence-led decarbonisation planning. We helped shape the CAP, know how to apply it in real-world local authority contexts, and bring the tools, insight and delivery experience needed to turn complex carbon analysis into practical strategy.
As one of the first projects to apply the CAP in this way, the work reinforced City Science’s position at the forefront of transport decarbonisation. It also showed how our combination of sector leadership, specialist expertise and in-house tools such as Cadence can help local authorities create locally relevant, decision-ready evidence bases and more deliverable pathways to net zero.