In this paper we investigate the monthly frequency and severitiy of road traffic accidents in Belgium from 1974 to 1999. We describe the trend in the time series, quantify the impact of explanatory variables, and make predictions. We found that laws and concerning seat belts, speed, and alcohol have proven succesful. Furthermore, road safety increases with freezing temperatures while sun has the opposite effect, and precipitation and thunderstorms particularly influence accidents with light injuries. Economic conditions have a limited impact. State-space methodology is used throughout the analysis. We compared the results of this study with those of earlier research that applied a regression model with autogregressive moving average errors on the same data. Many similarities were found between these two approaches.