Assessment of road traffic noise measurement strategies for urban noise mapping: a case study

Abstract Urban noise mapping relies on acoustic measurements that are often conducted using heterogeneous field practices, which can introduce variability in the acoustic data used for noise assessment and model calibration. This exploratory study investigates potential sources of variability in road traffic noise measurements, focusing on sound level meter (SLM) positioning and measurement duration. Using Santa Maria, Brazil, as a case study, noise data were collected at 54 locations across different land uses, pavement types, and traffic conditions, including acceleration, deceleration, road gradients, and proximity to crossroads. Simultaneous measurements with up to three Class 1 SLMs were performed to assess spatial variability. The results showed that the relationship between vehicle counting duration and noise measurement duration varied according to road type and traffic conditions, with longer sampling windows being required on some local roads with heavy-vehicle traffic. Under acceleration conditions, including locations downstream of traffic lights and uphill segments, sampling windows were generally 2 to 10 min longer than under corresponding deceleration conditions to remain within ±1 dB of the 60-min reference. For asphalt surfaces, the shortest sampling windows meeting this criterion at 40 m from crossroads ranged from 10 to 30 min, depending on land use and traffic conditions. For interlocking concrete block surfaces, 30 min was the shortest evaluated duration meeting the criterion in the residential scenario. On inclined roads, higher SPLs were observed at acceleration points on asphalt surfaces, whereas on interlocking concrete block surfaces, higher SPLs were associated with greater heavy-vehicle flow. These findings demonstrate that SLM positioning and measurement duration can influence measured SPLs under different road and traffic conditions and should be considered when designing road traffic noise measurement campaigns. The results provide case-specific evidence to support more consistent measurement practices and future investigations of noise-map calibration.