The negative impact of motorized private mobility on the environment can be decreased successfully by encouraging more people to carpool. From a psychological perspective, only little is known about the determinants of carpooling. Therefore, this study investigated carpooling behavior based on a theoretical background that integrates (1) the theory of planned behavior, (2) the norm activation model, and (3) dispositional trust. Additionally, we studied carpooling from two separate perspectives: Passengers sharing rides, and the drivers offering rides. We conducted a survey with a representative sample of 342 participants in Switzerland. The results showed that for both, passengers and drivers, normative aspects such as descriptive and personal norms, in combination with perceived behavioral control predicted carpooling intention. Attitude toward carpooling behavior, however, did not have any predictive power regarding carpooling intention, neither for passengers nor drivers. Dispositional trust displayed an indirect effect on intention to carpool as a passenger or driver via perceived behavioral control. Based on these results, we discuss practical implications for designing measures to promote carpooling successfully in the future.

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.