Leiden University invites applications for a fully-funded PhD position focused on the development of efficient artificial intelligence solutions for traffic management and decision support systems. This interdisciplinary project sits at the intersection of AI, machine learning, and real-world traffic operations, aiming to leverage foundation models such as large language models (LLMs) to enhance real-time decision-making in road traffic management. The research will address the integration of multimodal and instruction-tuned foundation models with operational challenges faced by traffic operators, municipalities, and mobility service providers. Key research activities include adapting LLMs for spatial-temporal data and traffic control domains, developing hybrid AI architectures that combine symbolic domain knowledge, real-time data streams, and probabilistic inference, and designing decision support tools capable of natural language interaction, scenario simulation, and action explanation. The project will also investigate the efficiency, robustness, generalization, and ethical implications of deploying foundation models in safety-critical infrastructure. The PhD position is a joint initiative between Leiden University and Technolution, a leading Dutch technology innovator known for its MobiMaestro traffic-management platform and FlowCube smart AI traffic camera. The successful candidate will work within the Leiden Institute of Advanced Computer Science (LIACS), a top-ranked computer science department in the Netherlands, and collaborate with a consortium of academic and industry partners. Responsibilities include conducting original research, publishing in peer-reviewed journals and presenting at international conferences, completing a PhD thesis within four years, engaging with other researchers and developers, and assisting in teaching activities. The position offers a supportive, diverse, and international work environment located in the heart of the Bio Science Park, with access to excellent facilities and career development opportunities. The employment package includes a competitive salary (€3,059–€3,881 gross per month), holiday and end-of-year bonuses, pension scheme, full reimbursement of public transport commuting costs, flexible working hours, options for sabbatical or paid parental leave, hybrid working arrangements, home-working allowance, and a university-provided laptop. Applicants should hold or be close to completing an MSc in computer science, AI, or a related field, possess strong programming skills (Python, PyTorch), be familiar with modern ML frameworks and large-scale models, and have excellent analytical and communication skills. Fluency in English is required. The application deadline is December 18, 2025. For more information about LIACS and the application procedure, visit the provided university links. Enquiries can be directed to Prof. Rob van Nieuwpoort (r.v.van.nieuwpoort@liacs.leidenuniv.nl).