Flexible models for accidents on Chilean roads.

The effect of both traffic flow and geometry on accidents is analyzed on the basis of a time series of a cross section of two-lane Chilean paved roads. Two linear specifications of functions explaining total accidents, accidents involving pedestrians (AIP) and the total less AIP, are compared against a flexible quadratic form. The results show that second order effects, particularly those of geometric characteristics, are highly significant; moreover, their omission causes a relevant downward bias on the marginal effect of flow on accidents. These results suggest that flexible forms are more appropriate for analyzing the contribution of flow and geometry to the level of accidents on a particular road section.