Alessandro Di Graziano

MULTICRITERIA ANALYSIS METHOD FOR PAVEMENT MAINTENANCE MANAGEMENT

Multicriteria analysis (MCA) provides a framework for breaking a problem into its constituent parts. MCA provides a means to investigate a number of alternatives in light of conflicting priorities. By structuring a problem within the MCA framework, alternatives may be ranked according to preestablished preferences to achieve defined objectives. A method developed for providing an MCA framework within the Highway Development and Management Tools, Version 4 (HDM-4) is described. Factors such as social benefits, environmental effects, safety impact, strategic importance of roads, and so forth have been included, within a unified decision-making framework. The analytic hierarchy process method was selected for HDM-4 because it transforms the analysis of competing objectives to a series of simple comparisons between constituent elements. The approach does not require a definition of trade-offs between the possible values of each attribute (i.e., it is not necessary to build utility functions), and it allows users to understand how outcomes are reached and how weightings influence outcomes. A pilot implementation checked the applicability of the analytical hierarchy process (AHP) method to road management and analyzed the effectiveness of outputs. Results obtained using HDM-4 economic criteria were compared with those produced by AHP. For the pilot implementation, the HDM-4 strategic planning application was chosen because it is the level in which, generally, medium- or long-term programs must be defined along with economic and other social and environmental aspects to justify budget allocations. Five main criteria were identified with regard to road maintenance budget allocations that constrain the decision-making process: comfort, environment, safety, road agency costs, and road user costs. Prioritization based on MCA more evenly distributes the available budget when compared with prioritization based on economic criteria, which tends to favor roads with high volumes of traffic.

Actual Driving Data Analysis for Design Consistency Evaluation

In recent years, researchers have proved that a consistent highway design ensures that successive elements are coordinated to produce harmonious and homogeneous driver performances and does not provoke unexpected events. Knowledge and practice show that drivers make fewer errors near geometric features that conform to their expectations. On this basis, the importance of identifying inconsistencies on highways for its significant contribution to road safety is emerging as an important feature in highway design. Although several techniques and models for evaluating the consistency of a design in a quantitative way have been identified and some countries have implemented the design consistency concept in their road design guidelines mainly in a qualitative way, there have been only a few efforts to measure actual driving behavior. The aim of this paper was to determine design inconsistencies on existing two-lane rural roads with the use of actual driving behavior by means of field data measurements and to verify their agreement with a consistency evaluation model. Furthermore, suitable equipment and a procedure for surveying driving dynamics and driver workload have been developed. In particular, driving behavior was assessed through direct measurements and parameters taken from data collected on a selected sample of test drivers by using a purposely designed instrumented vehicle. The vehicle, named the driver instrumented vehicle acquisition system (DIVAS), was driven under real traffic conditions on a two-lane rural road. The design classes of consistency of the test courses also were evaluated with a well-known safety criteria model. Data collection and treatment procedures are presented, and data analysis and results from this first experiment are given.

Road Traffic Conflict Analysis from Geo-referenced Stereo Sequences

In this paper an imaging system for road traffic conflict analysis is proposed. The system exploits geo-referenced stereo sequences and tracking procedure to compute traffic conflict measures which can be analysed by experts. Using the potentiality of the traffic conflict technique as a surrogate safety measure could constitute an effective tool in understanding how the driver interacts and adapts its behaviour with respect to the vehicle, the road characteristics, the traffic control devices and environment. Experiments performed on real data acquired in urban environment confirm the effectiveness of the system which makes simple and fast for the experts the understanding of the driver behaviour.

Surrogate Safety Measures for Optimizing Investments in Local Rural Road Networks

Safety management of the local rural road network is often constrained by low budgets and a variety of external local requirements. Moreover, for the safety management of these roads, where a screening of the network based on observed crashes can be affected by a lack of quality and an insufficient quantity of collision data, alternative analyses are needed to establish those circumstances that make a particular road intervention cost-effective. Cost versus safety trade-offs must be examined for a series of alternative projects. As a result of a research project funded by the European Commission, a safety index (SI) was formulated as a surrogate measure of safety. The SI is based on the safety features of the road segment, which are assessed by two methodologies: road safety inspections and design consistency evaluations and standards checks. Given the significant correlation found between SI values and the expected number of crashes, a methodological approach that uses the SI to evaluate the safety effectiveness of the alternative proposed investments is presented. Moreover, because often the available budget was not sufficient to undertake all alternative projects evaluated as being effective, a formal method for selecting projects to be included in the budget was applied to maximize the safety benefits of the investments. The procedure implemented in the SAFOPT software (safety optimization) makes it possible to identify the intervention strategies that produce the greatest safety benefits for variations in the SI while being compatible with the available annual budget, that is, the optimum budget to obtain the maximum benefit.

Evaluation of the effectiveness of ADAS in reducing multi-vehicle collisions

The use of new telecommunication technologies represents an important factor to improve road safety. In such context, simulations have been carried out in order to estimate the effectiveness of the Advanced Driver Assistance Systems (ADAS) on board of heavy vehicles. Specifically a general framework for safety evaluation of Adaptive Cruise Control (ACC) and Cooperative ACC (CACC) in rear-end collisions is described. Considering probabilistic distributions for reaction time, tyre performance, braking deceleration and vehicle time gaps, various Monte Carlo simulations were carried out for different values of traffic speeds and pavement conditions, so as to calculate the probability of multi-vehicle collision.

Safety Inspection and Management Tools for Low-Volume Road Network

On low-volume roads, where crash frequency is less than on high-volume roads, the role of procedures alternative to and complementing crash investigations becomes substantially more important; safety inspections as a proactive approach to road safety can be very effective for this class of roads. From the results of the European Union research report Identification of Hazard Location and Ranking of Measures to Improve Safety on Local Rural Roads, a safety risk index (SRI) was formulated as a measure of risk that uses the safety inspection as the primary source of information associated with design consistency assessment of the horizontal alignment. Moreover, because of its quantitative evaluation, the SRI can be used to determine benefits and a cost–benefit ratio of different intervention strategies. Then, since there are often situations in which the available budget will not be enough to undertake all the measures in the road network, an SRI-based optimization algorithm was defined for selecting projects to be included in the budget.

Context-Sensitive Approach for Network Selection of Infrastructure Projects

Context-sensitive solutions (CSS) aim to provide a systematic, comprehensive approach to project development from inception and planning through operation and maintenance. The goal is a procedure that provides an outcome that harmonizes transportation requirements with community needs and values. Multicriteria analysis can assist in the assessment of competing needs and provide a systematic approach to evaluation of the options. The CSS approach and multicriteria analysis were merged in an implemented procedure to select the most effective investment projects for solving a classical multiobjective optimization problem under budget constraints. The potential of this procedure was explored, and the steps required to evaluate this concept were identified. A case study was used to demonstrate the process and to identify future steps to ensure widespread application of the process.

How to Compare Different National Databases of HGV Accidents to Identify Issues for Safety Improvements

The objective of this paper is to present a methodological approach and a case study for an international comparison of accident data coming from different national databases. Safety levels and the characteristics of severe crashes involving heavy goods vehicles in different European countries (Italy, France, Germany, Great Britain and Spain) are analyzed. Considering that all the countries involved have different inventory structures for the variables reported in their national accident databases, the taxonomy theory was used in order to create a comparable structure for the database used in the analysis. The taxonomy is non-exclusive and the codes are categorical, denoting the absence or presence of a certain feature. Based on the data available in each national database the five European Union databases of accidents involving heavy goods vehicles have been referenced to only one, composed of 11 items (casualty class, injury number and severity, location, light conditions, road conditions, junction, vehicle type, driver age, driver gender, accident type and maneuvers) , which capture common features of heavy goods vehicles accidents. A statistical analysis was carried out in order to highlight significant differences in the proportions of heavy goods vehicles crash categories.