Research on Section Division of Freeway with Ordinal Clustering Method

The roadway section division is the first step to establish accident prediction model. Generally speaking, there are two methods in the roadway section division: One is fixed length method, namely the roadway section is divided into the fixed length, like 0.5 km (mile), 1 km (mile) and so on. The other is variable length method, in which the section division is usually conducted according to the changes of the independent variables, e.g. traffic volume, speed limit and geometric design elements like horizontal curvature, vertical grade, lane numbers, shoulder width, and so on. Regarding the freeway, both two methods have certain deficiencies. This study proposed a new method of freeway section division based on the ordinal clustering method, and the clustering index is the accident frequency per kilometer distributed along the roadway. Through example analysis, we discovered that accident frequency of each segment obtained by this method was obedient to certain probability distribution, which is beneficial to the model establishment, and this method has a good application value.