Global urbanisation and rapid economic growth have driven substantial migration to urban areas, accompanied by the spatial expansion of urban infrastructure, profoundly shaping mobility patterns and environmental outcomes (World Bank, 2024). Urban regions, comprising densely populated cores and sprawling suburbs, now account for a significant share of energy consumption and greenhouse gas emissions, with transport a major contributor (Department for Energy Security and Net Zero, 2023). Despite advances in technology and transport modes, accessibility to key activity hubs has declined, and reliance on private vehicles has increased, largely due to urban sprawl that lengthens distances between workplaces, shops, and services (OECD, 2020). Consequently, widespread congestion has become the norm in many cities, reducing quality of life through increased pollution and travel times (UN-Habitat, 2023). Many metropolitan areas lack sufficiently developed public transport systems to offer viable alternatives to private cars. Moreover, public transport often requires substantial subsidisation, and some routes operate with low ridership, making them economically unsustainable (World Bank, 2024). Fragmented administrative boundaries that fail to encompass entire metropolitan regions further hinder coordinated mobility policies, leading to inefficiencies, poor regional connectivity, and inconsistent fares or schedules (European Commission, 2024).Today, new mobility services and technologies present promising solutions to urban transport challenges, ranging from digital transport systems and Intelligent Transport Systems to vehicle electrification, shared mobility, and integrated multimodal platforms (McKinsey, 2024). Smart mobility innovations such as Mobility-as-a-Service, real-time traffic management, and connected infrastructure – have the potential to reduce congestion, cut emissions, and improve accessibility and quality of life in cities (UN, 2025). However, authorities face significant challenges in integrating these innovations into spatial and transport plans that enhance citizens’ wellbeing while meeting environmental targets. Key challenges include the need for multisector coordination, scalable digital solutions, meaningful data integration, and supportive policy frameworks (Mubiru and Westerholt, 2024). Given rapid technological advances, the proliferation of new mobility services, and ongoing urban sprawl, metropolitan authorities often lack the expertise, data, and tools necessary for effective multiscale spatial and transport planning (UN-Habitat, 2023; World Bank, 2024). Without addressing these institutional and technical gaps, the potential of smart mobility to deliver sustainable and equitable urban transport remains constrained.This themed issue brings together six papers that explore how city planners, engineers, and policymakers can drive the development and management of smart, sustainable urban transport infrastructure, providing insights to enhance efficiency, accessibility, and environmental performance in rapidly evolving cities.In the first paper, Wang et al. (2026) tackle the complex web of factors influencing traffic capacity, moving beyond simple statistical analyses to capture the interplay between traffic, control, and geometric variables. Using a structural equation model, the study examines key elements such as signal phase, signal cycle, all-red time, road type, lane width, number of lanes, lane location, heavy vehicle proportion, and administrative district. Path analysis highlights that signal phase number of lanes, heavy vehicle proportion, and administrative district most strongly affect capacity. The results underscore the value of adaptive signal control, targeted lane adjustments, and regulating heavy vehicle access to optimise intersection performance. By providing data-driven insights, this research equips urban planners and traffic engineers with actionable strategies to enhance traffic flow, improve safety, and boost the efficiency of urban mobility systems in rapidly evolving cityscapes.In the second paper of this issue, Oh et al. (2026) address a pressing challenge in sustainable urban mobility: keeping bicyclists safe in mixed traffic with autonomous and human-driven vehicles. The study evaluates left-turn passage methods including hook-turns, bike boxes with and without priority signals, and narrow lanes, using simulator data calibrated with real-world observations. Findings show that while hook-turns are effective at low traffic volumes, bike boxes with priority signals outperform all methods during peak periods and as autonomous vehicles become more common, enhancing both safety and efficiency. By giving bicyclists priority at key intersections, these measures reduce crash risks, waiting times, and conflicts with vehicles. The research not only advances understanding of bicycle–vehicle interactions in the era of autonomous transport but also provides actionable guidance for urban planners and policymakers. Prioritising cyclist infrastructure now is vital for creating safer, greener, and more sustainable cities.In the third paper of this issue, Harding (2026) places social equity and inclusivity at the heart of sustainable design by examining how different age and gender groups experience public circulation in London’s underground train stations. Applying the first three stages of the service design methodology including observation, synthesis, and idea generation. The study uses questionnaires to assess how vertical and horizontal circulation influence perceptions of inclusivity. Newly developed proxies, including comfort, security, confidence, gentleness, and awareness, alongside the concept of vertical severance, reveal how station layouts shape passenger experiences. The findings show that improving circulation design and minimising vertical severance can significantly enhance inclusivity for all users. By uniquely transferring service design method to the built environment sector, the research strengthens the link between inclusivity and the social equity pillar of sustainability. The study offers actionable insights for designers, architects, and policymakers, demonstrating how user-centred approaches can tackle ‘wicked problems’ and support more equitable, accessible, and sustainable public infrastructure.In the fourth paper, Sohail and Shahid (2026) explore sustainable retrofitting strategies for existing buildings to reduce energy consumption and carbon dioxide (CO2) emissions. Using building information modelling, the study implements green roofs and modifies wall and window materials in four low-rise buildings, analysing thermal transmittance, solar exposure, comfort levels, and carbon dioxide emissions. The results show significant improvements: retrofitting reduced U-values across roofs, walls, and windows, enhanced solar exposure, and substantially lowered carbon dioxide emissions. For instance, carbon dioxide emissions in the plaza building dropped from 88% to 31%, while the warehouse building’s comfort level increased from 26.6% to 78%. The study offers a practical framework for virtual retrofitting, providing guidance for energy-efficient design in both existing and new structures. Although limited to four buildings, the study recommends benchmarking, climate-specific retrofitting strategies.In the fifth paper of this, Zhu et al. (2026) investigate the potential of nano-alumina (NA) to enhance the performance of alkali-activated mortars incorporating ground granulated blast furnace slag (GGBS) and fly ash (FA). Using a comprehensive experimental programme, including mechanical testing, durability assessment, and advanced microstructural analyses, the study evaluates the influence of varying NA contents at 28 days. The findings identify 2% NA as the optimal dosage, achieving a peak compressive strength of 61.9 MPa alongside improved flexural performance, reduced sorptivity, and lower water absorption. Although increasing NA content reduces flowability, microstructural evidence confirms enhanced gel formation, matrix densification, and pore refinement. Crucially, the use of FA and GGBS delivers substantial carbon footprint reductions of ≈50%–80% compared with conventional cement-based materials. By coupling enhanced mechanical performance with clear environmental benefits, this research positions nano-modified alkali-activated mortars as a promising solution for durable, high-performance, and low-carbon construction.The sixth and final paper in the issue, Jiang et al. (2026) address a major barrier to the wider adoption of inherent defects insurance in construction: the lack of intelligent, digitalised approaches to rate determination. Traditional inherent defects insurance pricing relies heavily on manual judgement, resulting in limited differentiation, low transparency, and weak developer engagement. To overcome this, the study integrates case-based reasoning and random forest algorithms within a digital inherent defects insurance rate-setting framework. Using the analytic hierarchy process to weight critical attributes, the authors construct a digitised case library of 17 inherent defects insurance projects and apply random forest to support both case retrieval and intelligent rate prediction. The results show that case-based reasoning performs effectively when strong historical similarity exists, while random forest delivers robust predictions when similarity is low. By embedding artificial intelligence into inherent defects insurance pricing, this research advances data-driven decision making and lays the foundation for a more transparent, scalable, and intelligent inherent defects insurance system, with strong potential for future expansion as data availability increases.In summary, this issue underscores the evolving role of engineering in addressing global sustainability challenges through innovation, digitalisation, and inclusive design. The featured papers collectively demonstrate how data-driven methods, advanced modelling, user-centred approaches, and artificial intelligence can enhance urban mobility, improve safety and social equity, decarbonise buildings and materials, and strengthen construction governance. Together, they point towards a future in which resilient, low-carbon, and inclusive engineering solutions are central to shaping sustainable cities and infrastructure.
Renukappa et al. (Thu,) studied this question.