Addressing gaps in the understanding of killed and seriously injured casualties impacts of engineering treatments for A-roads
This project aims to improve understanding of whether longitudinal road markings and junction treatments affect driver behaviour and help reduce people killed or seriously injured (KSIs) on A roads.
The project responded to evidence gaps identified previously through our Road to Zero Harm research, which highlighted there was limited national understanding of how these engineering measures influence driver behaviour, collision likelihood and severity. The work built the evidence needed to support confident and cost-effective use of these treatments across the Strategic Road Network (SRN) and to further improve our safety programmes.
National Highways faces an ongoing challenge in reducing deaths and serious injuries on A roads, where collision risk is influenced by road layout, driver behaviour, and the performance of existing engineering treatments.
Our Road to Zero Harm research previously highlighted that common treatments such as longitudinal markings and junction layouts are not being used to their full potential because there was limited national evidence about their influence on safety outcomes. This uncertainty reduces confidence in design decisions, making it harder to prioritise the most effective safety measures.
A clearer understanding of how these treatments affect real world risk is essential for better targeting of interventions and for achieving meaningful safety improvements across the network.
Objectives
Improve understanding of how longitudinal treatments influence driver behaviour, collision likelihood, and collision severity on A roads.
Improve understanding of collision patterns and risk factors at junctions, assess the effectiveness of junction interventions and recommend approaches for maximising safety impact.
Identify where these treatments are most likely to deliver the greatest contribution to KPI1 and ensure that future decisions are evidence informed. The KPI1 target is to reduce the number of people killed or seriously injured (KSI) on the strategic road network by 50% by the end of 2025, using a 2005–2009 baseline.
Identify and explore barriers to delivery, including feasibility considerations and alignment with current standards.
Success criteria
Clear evidence describing how longitudinal treatments influence driver behaviour, collision likelihood, and collision severity, suitable for informing design decisions.
Clearer understanding of collision risk at junctions, supported by evidence on the factors that contribute to severe incidents and the effectiveness of relevant interventions.
Practical criteria or insights that help identify where these treatments are most likely to deliver meaningful reductions in deaths and serious injuries on the SRN.
Clear articulation of feasibility and standards considerations that need to be addressed in future implementation phases.
How the project supports National Highways KPIs
Safety improves through stronger evidence on how engineering treatments influence collision likelihood and severity across A roads, supporting reductions in deaths and serious injuries on the SRN.
Efficiency improves by enabling more targeted and cost-effective investment in treatments that offer the greatest potential safety benefit.
The approach
The project built on the Road to Zero Harm research by reviewing available national and international evidence on how longitudinal treatments and junction layouts influence driver behaviour, collision likelihood, and collision severity on A roads.
This included examining raised profile markings, central hatching, and edge treatments, alongside analysis of junction collision patterns to understand why junctions account for a substantial proportion of deaths and serious injuries on the SRN.
Engagement with National Highways specialists helped identify practical challenges such as feasibility considerations and the Design Manual for Roads and Bridges (DMRB) alignment that currently affect the wider use of these measures.
Insights from internal consultation were used to focus the work on areas where specialists face uncertainty, ensuring that the research addressed gaps affecting design confidence and treatment selection.
The approach also set a foundation for future work, where further analysis, simulation and controlled testing may be required to strengthen the evidence base needed for confident decision making across the SRN.
Project obstacles and how they were addressed
The project encountered several challenges linked to limited national evidence on the effectiveness of longitudinal treatments, uncertainty about collision patterns at junctions and practical constraints affecting implementation. Much of the available research originated from overseas, creating scepticism about its relevance to A roads in England.
The earlier Road to Zero Harm work also indicated that deaths and serious injuries at junctions may be underreported in official statistics and that existing evidence did not provide clear recommendations for treatments. In addition, some longitudinal measures are not fully aligned with DMRB, raising feasibility concerns and limiting wider application.
These considerations shaped the focus of the research and highlighted where clarity is needed to support confident design decisions.
- Limited UK specific evidence was managed by reviewing international studies alongside practical insights to understand where findings may be applicable or require further investigation.
- Unclear effectiveness at junctions was addressed by drawing on Road to Zero Harm findings to focus the review on collision patterns and risk factors that may not be fully captured in current data.
- Feasibility and DMRB alignment were explored through engagement with specialists to clarify constraints that affect implementation of longitudinal treatments.
- Uncertainty was addressed by incorporating feedback from internal consultation, ensuring the research reflected real world concerns about confidence and usability.
Outcomes and impact
The project has further strengthened our understanding of how longitudinal markings and junction treatments may influence driver behaviour, collision likelihood, and collision severity on A roads. It clarified where evidence is strong, where uncertainty remains and why limited UK specific research creates challenges for confident design decisions.
The work also highlighted key factors behind collision risk at junctions and identified where further investigation will be needed to support future guidance, appraisal, and the next phase of research.
Key outcomes include:
- Clearer visibility of existing evidence on how longitudinal markings and junction layouts may influence behaviour and safety outcomes.
- Improved understanding of evidence gaps, especially where overseas research may not directly apply to the SRN.
- Better insight into junction related collision patterns, supporting further investigation of why these incidents may be underrepresented.
- Greater clarity on feasibility and standards constraints, including where DMRB alignment limits deployment of low-cost treatments.
- Stronger foundation for follow-on research, including simulation, controlled track testing and stakeholder consultations in the next project phase.
User and stakeholder outcomes
The project has helped specialists gain clearer visibility of the current evidence surrounding longitudinal markings and junction treatments, particularly where uncertainty about UK applicability has limited confidence in their use.
Feedback highlighted through the Road to Zero Harm consultation showed that engineers have concerns about relying on overseas studies and about the feasibility of applying some treatments within current standards.
By clarifying these considerations and highlighting the areas where further investigation is needed, the project supports more informed discussions among designers and safety specialists as they consider future guidance and evidence needs for A road safety improvements.
Key insights and learning
The project highlighted where limited UK-specific evidence and practical constraints reduce confidence in the wider use of longitudinal markings and junction treatments on A roads. Reviewing available research and practical feedback clarified which factors influence treatment effectiveness and where further investigation is needed to support more confident, evidence informed decisions in future phases.
- Low-cost treatments may be underutilised, as evidence gaps and standards related constraints limit confidence in deploying measures that show strong potential overseas.
- Understanding behaviour mechanisms is essential, because the reasons treatments influence driver behaviour is not well evidenced for UK conditions.
- Junction-related risk is likely underestimated in official statistics, with initial research indicating that deaths and serious injuries at junctions may be higher than current figures suggest and that clearer evidence on effective interventions is needed.
- Scaling treatments requires clear criteria, as mass action depends on knowing where measures are appropriate and likely to have the greatest impact.
- Further research will be essential, including activities such as simulation, controlled track testing and stakeholder consultations, to address remaining evidence gaps.
Future value and next steps
The next phase will build on this year’s findings by carrying out the deeper analysis and targeted testing needed to strengthen the evidence base for longitudinal markings and junction treatments on A roads. This work will focus on addressing the remaining evidence gaps identified in this phase to support more confident and evidence informed design and implementation decisions across the SRN.
- Undertaking simulation studies and controlled track testing, including motorcycle safety testing of different marking types.
- Stakeholder consultations including working with specialists and the industry to explore remaining feasibility and standards considerations.
- Developing evidence informed implementation strategies that identify where treatments are likely to deliver the greatest safety impact.
