Effects of traffic speed reduction interventions on noise-induced annoyance and self--reported sleep disturbances: a longitudinal study in Zurich

For the purpose of evaluating acceptance and effects of permanent speed reductions on noise level, noise annoyance and self-reported sleep disturbance, we surveyed about 1300 randomly sampled inhabitants, before and after a speed regime changeover from 50 km/h to 30 km/h along 15 small- and mid-sized city streets in Zurich. Concurrently, individual noise exposure calculations based on traffic counts and on-site speed measurements were carried out. The results show a decrease of road traffic noise levels at the loudest facade point by an average of 1.6 dB during the day and 1.7 dB at night, a significant decrease of road noise annoyance and of self-reported sleep disturbances as well as a significant but moderate increase of the perception of road safety. Most importantly, the exposure-response relationships for annoyance and sleep disturbance were shifted towards lower effects in the 30 km/h condition by, depending on receiver point, between about 2 and 4 dB during the day and about 4 dB at night, indicating lower effects at the same average level. We conclude that besides the lower average level alone, additional factors related to the lower driving speed must play a role in the reduction of annoyance and sleep disturbance.