Estimation of Accident Frequency at Newly-built Roundabouts in the Czech Republic

Roundabouts have become one of the most popular traffic easing and safety improving measures implemented on roads in the Czech Republic. The decision on the realization of each new roundabout should be based on the knowledge of the expected realization costs and benefits resulting from the future operation, especially changes in traffic and safety performance. This study introduces a negative binomial regression model that enables the quantification of the safety performance of roundabouts in terms of accident frequency in relation to their traffic and geometric characteristics. Model design and estimation of parameters is based on the sample of 90 roundabouts situated on all types of roads in the Czech Republic. Results suggest that the number of accident depends on the number of lanes on entering arms, vehicle speed in the vicinity of roundabouts, width of traversable apron and, of course, also on the annual average daily traffic. Resulting model structures is in accordance with structures of accident prediction models used in other EU countries and the US. Certain differences can be found in the degree of effects of particular model variables.