The analysis of road accidents carried out through scientific criteria has verified that a remarkable percentage of the accidents is due both to the consideration of the unsafe behaviours induced in the drivers by the road itself, and to the raising of the subjective threshold of risk coming from an inadequate offer of service. In recent years, thanks to precise community orientations, such conclusions have turned national and international research towards the study of the cause/effect relationships that regulate road operations and condition its safety.
Also in recent years some remarkable results have been achieved on the scientific plan thanks to the involvement of different disciplines and to the validation of the experimentation in virtual reality.
The result of these studies allows one to affirm that today conditions are mature for the last step in the path of a research, the translation of the theoretical acquisitions in criteria of planning fit to the demands of the modern driving conditions, as it should be for each branch of the engineering sciences.
The main aim of the project was to scientifically formalise some reliable procedures to appraise the quality of the road projects under the profile of the safety, both for the new realisations and for the rehabilitation of the existing network, taking into consideration the behaviors which the drivers assume when faced by the physical and functional characteristics of the rural road infrastructures in different traffic conditions.
The research’s main objective was to scientifically investigate and to update the traditional logics of the road planning by taking into account the mutual relationships involving the user, the road and its conditions of fruition in order to determine objective risk situations.
Moreover the project aimed at demonstrating that it is possible to verify the level of service of a road and the quality of the road design through an articulated system of 'indicators' that broadly overcome the limits of the traditional criterions of projects and are able to explain and to foresee the driving 'mistakes' that are solicited by the local and system structural characteristics of the road environment. Such indicators, verified during this project both on the field and in virtual reality, are able to assess:
- the complexities of the road environment that influence the appreciation of the visual message for the user, and how they condition the mental workload and fatigue processes;
- the influence of road geometries, tested in interactive environment, on the single user’s behaviour in terms of the effects they produce on the speeds of transit, on the configuration of the elementary and composed manoeuvres, on the dispersion of the trajectories, etc.
- the thresholds of risk assumed by the user when the conditions of the road change, after emphasising particular reference to the levels of uneasiness coming from vehicular interferences.
The resulting picture leads us to conclude that conditions are mature for translating these acquisitions into a 'theory of the road infrastructures', which can manage the planning and verify the levels of quality under the safety profile .
Such belief is at the base of the present project whose main aim is to reach a validation of a system of measures, certified experimentally, for the expression of judgment of the road infrastructure’s systemic quality, which is tightly correlated to the levels of '
The project was articulated in two phases:
- the expected result of the first one is the identification of a set of indicators for the description of the safety performances of the road;
- in the second one a scientific procedure to test the quality of road project has been developed, in relation to prefixed thresholds of expected accidents.
The operative 'footsteps' of the research’s first phase included:
- the selection of a suitable system of indicators fit to express the systemic quality of the infrastructure in relation to the spontaneous and induced user’s behaviours when they vary according to the changing of the physical road characteristics and conditions of service in different situations of circulation;
- the checking of the expressiveness of such indicators that have been noticed on the field and that are able to represent the complexity of the cause/effect relationships regulating the accident phenomenon, both with regard to the geometric and functional characteristics of the infrastructure, and to the solicitation of safety behaviours in different conditions of fruition;
- the continuous acquisition and the calibration of analogous indicators noticed in virtual reality when the traffic flow and the more significant environmental conditions change through a suitable sample of test drivers in scenarios that are shaped in such a way as to reproduce the road situations investigated on the field with the greatest possible realism.
The operative 'steps' of the second phase of the research proposed:
- the study of the correlations that determine among the functional indicators acquired on the field and noticed in virtual reality with the accident scenario that characterises the road infrastructures taken into examination;
- the formalisation of the criteria for the systemic check of the project’s property both for new realisations, and for the rehabilitation of existing roads;
- the validation in Virtual Reality of the assumed criteria comparing the experimentally-acquired indicators to pre-fixed thresholds.
The results here are summarised relating to the two mentioned project phases. The results of the first phase are only in function of the main objective and are useful to the validation of a new approach to the road design. It puts the driver at the core of any decision making process in order to identify the systemic functions of the road.
In this sense the results that have been obtained are:
- the identification of the psycho-physiologic variables that are relevant in driving;
- the validation of the correlations between the variables and the cause/effect processes that determine accidents;
- the calibration of numerical indicators useful to check how the mentioned correlations have consequences on drivers' behaviour as the operability in road conditions change.
The results obtained in the second phase coincide with the objectives of the project. These results are particularly relevant to assure the intrinsic safety of the road, adopting experimental methods for performances evaluation, considering the relationships among road, driving conditions and stresses on drivers that affect hazardous reactions, including:
- the validation of the computational model of drivers’ behaviours in different driving conditions;
- the formulation of criterions for the systemic validation of the quality of a road project, evaluating in Virtual Reality the adequate indicators to check and optimise the technical choices in terms of acceptable accident levels.
Numerical analysis brought into light the conditions of traffic that are relevant to the cause/effect relationships in causing accidents. More precisely it is important to distinguish the following two:
- low volume traffic (traffic flow N/C<0.25): the road geometry is the primary variable that, together with the meteorological conditions, has effect on the accident scenario;
- high traffic flow (traffic flow>0.25): the traffic flow is what has mostly effect on the accident scenario.
In relation to the first condition it has been identified an indicator based on the consequences of the geometries rather than on their consistency. In particular the micro-corrections that the drivers make during driving as the geometry changes have been found as very expressive of unsafe conditions. More in depth it has been found that the horizontal alignment is mostly relevant and the vertic
T1: The project has brought into light the main psycho-physiologic variables that affect safe drivers’ behavior. These variables are to be considered by designers and practitioners in road project development phases as preconditions for road safety.
T2: The scientific procedure that has been proposed and experimentally validated in the project can be assumed for Road Safety Audit both for rehabilitation of existing roads and for new infrastructures.
T3: The same procedure could be today adopted as standard for Road Safety Impact Assessment also for the TREN network, as requested by the recent EU Directive about infrastructure safety.
T4: Additional studies should be done to calibrate the procedure at the EU level. Considering different driving habits, road environments and rules.
T5: Two consistent indicators have been validated to analyse the safety standard respectively for low-volume roads and for high traffic conditions.
P1: The results of the project show that any safety policy at the European or National level has to assume a multidisciplinary approach. Any traditional study from one disciplinary perspective neglects relevant aspects of the problem.
P2: The investments for advanced technologies development as driving simulators should be supported and improved.
P3: Multidisciplinary networks at EU level should be encouraged to exchange knowledge in the field of road safety. Especially engineering and safety experts, psychologists, advanced technologies specialists should play the most relevant role.