Comparative Safety Analysis of a Two-Lane Two-Way Major Highway, Using IHSDM and a Portuguese Procedure

Abstract

The Interactive Highway Safety Design Model (IHSDM) is a software tool for evaluating safety and operational effects of alternatives in highway projects, which is available through the US Federal Highway Administration (FHWA). IHSDM can be applied in the design of new highways and in the major redesign of existing highways. The software contains five modules, intended for the evaluation of measures describing relevant aspects of the expected safety and operational performance of a highway design. Three of these modules are potentially relevant for use outside the US: the Crash Prediction Module, the Design Consistency Module, and the Traffic Analysis Module. A procedure for the detection of inconsistent horizontal curves in single carriageway rural roads of the National Road Network and the improvement of their safety records was developed at the National Laboratory of Civil Engineering (LNEC) for application in Portugal, using driver behaviour and safety data collected in the national context. The procedure may be applied automatically using the dedicated software PERVEL – Dangerous Curves Detection System. Within the context of the redesign of a dangerous stretch of single carriageway two-lane highway in the mountainous area in the North of Portugal, operational and safety data were collected and used in the analysis of its safety performance. Both IHSDM and the Portuguese procedure were used in this analysis. This was due to the fact that speed profiles in PERVEL are calculated considering horizontal geometric characteristics only, hindering its direct application in roads in mountainous areas, whereas relevant IHSDM modules includes both horizontal and longitudinal profile characteristics. IHSDM is suited for application under North American traffic conditions, which forced the recalibration of particular parameters for its application at the relevant Portuguese road stretch. In this paper a comparison is made between the results obtained using both procedures, in what concerns the detection of inconsistent horizontal curves and dangerous non-intersection sites. The main issues arising from the calibration of the crash prediction module to the Portuguese context are described.