Sustainable development requires ensuring the mobility of residents and must not cause deterioration of the quality of the environment in the selected area. The purpose of this study is to verify if the construction of a cross-regional highway through the city centre affected air quality in the neighbourhood of a newly built road. Air quality was assessed based on measurements of concentrations of nitrogen dioxide, which is considered to be typical for automotive sources air pollution. The spectrophotometric method with passive sampling was used in the 24 h NO2 measurements. The calculated mean NO2 concentrations in the periods before and after road construction were within the ranges of 23.2–31.9 μg/m3 and 22.3–28.9 μg/m3, respectively. The relative NO2 concentrations determined in the study for 10 out of 11 sampling points were lower than the unity, including 5 points markedly lower (0.82–0.89). The obtained results indicate that the construction of the new artery by the city centre, using appropriate technical solutions and traffic organization (tunnel, noise barriers, roundabouts, speed limit) likely contributed to an overall reduction in NO2 concentrations. The presented solution may serve as an example for other cities struggling with problems of low air quality associated with inefficient transportation systems.