Results of general linear mixed models (GLMM).

The dependent variable in each model is the ratio of the pollutant parameter measured at the comparison location to that measured at the roadside location. Categorical variables for wind direction use calm wind conditions as the reference category and barrier type categorical variables use the chain-link fence barrier as the reference. The first row in each box is the parameter estimate while the second and third rows are the lower and upper 95% confidence intervals (respectively).