Abstract Birmingham New Street Railway Station has recently undergone a substantial redevelopment at a cost of more than £600 m. However, the unique underground geography of the platforms has remained virtually unchanged which means that diesel exhaust gases are effectively trapped causing a daily build-up of air pollution in the station. A new ventilation system has been installed consisting of 98 bidirectional fans which are meant to disperse any air pollution out of the station. Unfortunately, the fans are triggered by carbon dioxide levels which do not significantly correlate with more serious air pollutants such as nitrogen oxides. The Office of Rail and Road, as the health and safety regulator, is responsible for ensuring that rail employers, such as Network Rail the station operators, comply with the relevant health and safety law. In August 2018 new Workplace Exposure Limits were introduced for Nitric Oxide and Nitrogen Dioxide and this paper shows that during a recent measurement campaign in 2016/17 one of the new Limits would have been exceeded on most days. Public Health thresholds, more applicable for passengers, were also compared using the Daily Air Quality Index which was equalled or exceeded every day. Network Rail have therefore undertaken to introduce a number of interventions which include: installing new NO/NO2 sensors to drive the ventilation system together with new more reliable wind sensors; encouraging Train Operating Companies to switch off idling diesel engines and to encourage more electric/hybrid trains. External funding details