Road traffic noise

Road traffic noise levels were estimated using the validated model system, Nord2000,³¹ and traffic data from a national road and traffic database. The Nord2000 calculated noise contribution from roads within a 3-km radius from the participants’ residential addresses. Input data of the Nord2000 include address, geocodes, apartment height above street level, road lines with information on annual average daily traffic volume, composition, speed, road type, and properties (e.g., motorway, rural highway, roads wider than 6 m, and other roads), and building polygons for all surrounding buildings. In addition, meteorological information, including wind speed and direction, air temperature, and cloud cover, was used in the Nord2000 model. The Nord2000 method has been validated by 544 propagation cases, including nine cases with the calculation of the annual mean of A-weighted 24-hour noise mean levels from a road, covering propagation distances up to 300 m. The validation study showed that the difference between modeled and measured values of the road traffic noise was less than 0.5 dB and had a standard uncertainty of <1 dB.³²

We calculated the annual average road traffic noise levels for the participants’ residential addresses from 1970 to 2014. For the year that participants changed the address, we calculated annual road traffic noise levels at the year of an address change as the mean of levels at two addresses (the old address and the new one). Estimated as the equivalent continuous A-weighted sound pressure level (LA_eq) at the most exposed façade of the dwelling, annual road traffic noise levels were estimated for the day (L_d, from 07:00 hours to 19:00 hours), evening (L_e, from 19:00 hours to 22:00 hours), and night (L_n, from 22:00 hours to 07:00 hours). Weights of 5 and 10 dB for the evening and night hours, respectively, were given when we calculated a weighted mean of 24-hour noise levels (L_den). As we had data on noise exposure from 1970 to 2014 and intended to link the noise exposure to the year before the end of follow-up, we considered maximum exposure length up to 23 years. We calculated 1-, 3-, and 23-year running means of the noise levels to explore distinguished associations of incident MI with different exposure windows and assigned the multiyear residential exposure to road traffic noise in a yearly time interval between the baseline year and last year of follow-up (Supplementary Material, Figure S2; http://links.lww.com/EE/A134). We chose three exposure windows: 1-year running mean to explore the effect of most recent and acute exposure to noise preceding year of MI diagnosis; 23-year mean, which is the longest available mean level (road traffic noise available since 1970), to examine the effect of chronic exposure to noise over many years, as a proxy of lifetime exposure to noise; and 3-year mean, which is the longest available mean exposure for PM_2.5 (available since 1990), which we consider as an important confounder. In addition, various exposure times of day for road traffic noise (L_d, L_e, L_n, and L_den) were also considered separately.