Discussion papers in statistics and econometrics 1/11
The work at hand tries to identify factors that explain accidents on German Autobahn connectors. To find these factors the empirical study makes use of count data models. The findings are based on a set of 197 ramps, which we classified into three distinct types of ramps. For these ramps accident data was available for a period of 3 years (January 2003 until December 2005). The Negative Binomial model proved to be an appropriate model for our cross-sectional setting in detecting factors that cause accidents. The heterogeneity in our dataset forced us to investigate the three different types of ramps separately. By comparing results of the aggregated model and results of the ramp-specific models ramp-type-independent as well as ramp-type-specific factors were identified. The most significant variable in all models was a measure of the average daily traffic. For geometric variables not only continuous effects were found to be significant but also threshold effects.