Reliable motor vehicle emission predictions are needed to ensure sound policy decisions. This study reports on a comparison between measured in-tunnel fleet emissions and predictions made with two new Australian vehicle emission software programs (COPERT Australia and PΔP) for one air pollutant: nitrogen oxides (NOx). Measurements were taken from a 6.8 km tolled motorway tunnel that links several major roads in Brisbane, Australia. The validation study suggests that modelled vehicle emissions of NOx are similar to those measured in the tunnel with a prediction error less than ±25% for both light-duty and heavy-duty vehicles. A possible reason for the difference is a suspected younger and cleaner fleet in the tunnel as compared with the Queensland average fleet. Further analysis of license plate information is anticipated to verify this.