Economic Appraisal and Optimization Process in Road Geometric Safety Improvements

For making decisions in optimizing investments in road safety projects, it is required to establish a regular process for selecting the most suitable countermeasures to be provided to road safety planners and decision-makers. Using the model developed in this research, a given budget funded from the road agency may be distributed among all predetermined locations (sites or routes), considering: (1) applying the share assigned to each location, the best possible improvements are selected as the premiere strategy amongst all alternatives through which the highest benefit is resulted, and finally, the sum of net benefits for all locations is maximized, and (2) the sum of construction costs attributed to selected alternatives in all locations does not exceed the total project budget. A set of road safety measures is studied involving the items known as geometric features and road design criteria. The features defined here consists of lane width and road surface quality, roadside hazard zones, horizontal curves, crest vertical curves and narrow bridges. The cost-benefit analysis and binary integer programming methods are used to develop economic appraisal and complete optimization tasks. The Solver program (as an add-in to Excel) is the main tool to run the allocating process. The research economic appraisal and optimization process consist of eight steps within which some criteria are applied to define, valuate, discount and compare the cost and benefit components of the analysis. The most important measure to estimate the safety benefits is a mediator variable which is broadly known as Accident Modification Factor (AMF). In this research, AMFs are extracted for each geometric feature mentioned above using the current valid accident models in Iran. As a means to support the execution of the developed model, a software program contributing to running the process of resource allocation is provided.