Generally, statistical data show that more than 50% of fatal traffic accidents occur on rural two-lane roads, with over half being related to horizontal curves. Accident locations indicate that road alignment consistency has a significant impact on accident occurrence. Many crash prediction models and road design consistency models have been developed, mostly based on operating speed and road geometric characteristics. In this paper, the Interactive Highway Safety Design Model (IHSDM) was used to analyse the consistency of road horizontal and vertical elements, as well as to predict the number and type of crashes on a section of the state road DC1 from Vrlika to Hrvace, covering a length of approximately 24 km. Two modules within the software were utilized: the module for predicting the number and types of accidents (Crash Prediction Module - CPM) and the consistency of the road alignment module (Design Consistency Module - DCM). In this regard, two types of road alignment consistency analyses were conducted: one according to the Croatian road design guidelines and another using the IHSDM tool. Furthermore, a comparison between the estimated and actual number of accidents was performed. The comparison showed that the number of accidents predicted by the IHSDM software does not deviate significantly from the actual number of traffic accidents on the analysed section. Based on the results of the conducted analyses, locations along the road section with reduced safety were identified, and infrastructure measures were proposed to improve traffic safety, specifically in terms of reducing the number of accidents.

IHSDM; traffic accident; road design consistency