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Most geometric design standards recommend the use of clothoids when connecting tangents and circular curves to produce a smooth, pleasing alignment. Despite the advantages of using clothoids, there are also possible adverse effects and literature results do not yet provide definitive results on clothoids effectiveness. Since the effect of clothoids is still an open issue, this paper provides a contribution in the evaluation of the effect of clothoids on curve negotiation on two-lane rural highways by a driving simulator experiment. The study is carried out evaluating the combined effect of different curve radii, deflection angles, and curve directions. Sixty-eight participants were involved in the study. The experiment was conducted in the VERA (Virtual Environment for Road sAfety) dynamic-driving simulator, operating at the Road Safety Laboratory of University of Naples Federico II in Italy. The variables are: clothoid (2 levels: with and without), curve radius (four radii: 125, 200, 400 and 800 meters), deflection angle (three angles: 20, 40 and 60 degrees), and curve direction (left direction in the outer lane and right direction in the inner lane). Trajectory dispersion and lateral position were used as measures of driving behaviour. Study results show that the clothoids produce significant advantages, reducing the lateral position variability, the maximum and minimum lateral positions, and the number of departures in the opposite lane and in the shoulder. The greatest effectiveness is shown in the curve approach. Clothoids are effective on all curves tested but the effect on the curves with radius equal to 800 m is quite smaller than on curves with radii of 125, 200, and 400 m.

Horizontal curves of two-lane rural highways are among the most dangerous elements of the road network. Despite this obvious and well safety issue, several geometric design standards are based on hypotheses which are often violated, such as: design speed different from the operating speed, constant speed through the curve, and driving at the center of the lane. In the experiment, the VERA (Virtual Environment for Road sAfety) high-fidelity dynamicdriving simulator, operating at the TEST (Technology Environment Safety Transport) Road Safety Laboratory located in Naples (Italy), was used. To validate the VERA driving simulator speed data, comparison between real-world and driving simulator speed data was performed in a previous study. The comparison showed that there were not significant differences between the real and the simulated speed samples. A two-lane rural highway with lane width equal to 3.50 m and shoulder width equal to 1.25 m was simulated. The experimental route consisted of the succession of 20 tangents with length equal to 1,000 m and curves with radius equal to 400 m and deflection angle equal to 35 degrees (L = 190 m). The tangent-to-curve transition was carried out by spiral curves with length equal to 55 m (A = 150 m), which corresponds to 2.0 s at 100 km/h. Thirty participants were recruited for the experiment. Seven subjects, 5 women and 2 men, exhibited simulator sickness and did not complete the experiment. Twenty-tree participants, 13 men and 10 women with age ranging between 23 and 55 years (mean = 35,2 years; s.d. = 9,3 years) and valid Italian driving licenses from more than four years (mean = 15,5 years; s.d. = 10,0 years), completed the experiment. Driving speed in the first two curves were significantly different from the speeds in the other curves, because of the adaptation phase. These curves were removed from the analysis and only the remaining eighteen curves were used in the analyses. Operating speeds were compared with operated speeds obtained through speed prediction models calibrated in world experiments in Italy in roads with similar alignments and the differences were less than 10 km/h. Speeds in left curves and right curves were compared. Statistically significant differences were not observed. Average decelerations were equal to 0.64 m/s2 whilst average acceleration were equal to 0.47 m/s2. The minimum speed of the operating speed profile was close to the beginning of the curve. Analysis of lateral positions showed that before the spiral drivers move away from the curve whilst in the circular portion of the curve they drive closer to the inside of the curve. In the exiting spiral drivers tend to move toward the outside of the curve. Overall, drivers tend to cut the curve (+ 0.25 m at the beginning of the spiral transition, - 0.5 m at the center of the curve). Lateral positions (relative to the axis of the lane) were significantly different ( < 0.05) in left and right curves, with a greater shift towards the inside of the curve for right curves

Durante la loro marcia alcuni veicoli abbandonano la corretta traiettoria di marcia e fuoriescono dalla carreggiata. Ai margini della piattaforma stradale molto spesso sono presenti ostacoli di varia natura contro cui possono impattare i veicoli in svio o delle aree ad elevato pericolo per i non utenti della strada. Tra di essi compaiono gli alberi, i pali della luce, i muri di sostegno, le pile dei ponti, le scarpate dei rilevati, i bordi delle opere d’arte, le strade parallele, i corsi d’acqua, le aree di parcheggio, gli edifici etc. L’incidente per fuoriuscita è tutt’altro che poco frequente e le conseguenze che si hanno sono molto severe. Il tecnico incaricato di valutare, e se necessario migliorare, la sicurezza dei margini di una strada deve esaminare varie alternative per ogni ostacolo. La sua scelta deve ricadere su quella che, in termini di protezione e di investimento, soddisfa i requisiti minimi di normativa e che nel contempo è la più conveniente. Le ipotesi che egli deve considerare includono: quella di non effettuare alcun intervento protettivo, la rimozione dell’ostacolo (o il suo allontanamento) e la protezione con dispositivi a diverso grado di contenimento. Un aspetto essenziale che il tecnico deve tenere in conto quando considera l’impiego di questi ultimi è che la loro efficacia, e quindi la loro convenienza, è legata al modo in cui vengono installati ed alle caratteristiche del sito in esame. La protezione offerta infatti dipende dall’estensione dell’installazione, dalla distanza dell’ostacolo, dalla distanza ove viene collocata la protezione rispetto al bordo della carreggiata, dal supporto offerto dal margine stradale, dalla curvatura di quest’ultimo nel caso degli accessi, dalla conformazione delle scarpate o del territorio immediatamente ai margini della strada, etc. Nella sua attività di selezione dell’alternativa più conveniente il progettista deve inoltre anche considerare l’opportunità di agire attivamente nei riguardi della riduzione del numero di fuoriuscite attraverso il miglioramento dell’aderenza, l’impiego di bande rumorose ai margini della carreggiata, l’uso di segnaletica particolarmente efficace nei punti di maggiore pericolosità, etc. Le disposizioni normative italiane attuali (il D.M. 5 novembre 2001, il D.M. 21 giugno 2004, la direttiva del 25 agosto 2004, la circolare del 21 luglio 2010 ed il decreto del 28 giugno 2011) indicano al progettista in maniera sommaria gli ostacoli ed i luoghi che è necessario proteggere, le classi minime dei dispositivi da adoperare ed alcuni principi da considerare nella progettazione dell’installazione. Esse da sole non sono sufficienti per un’appropriata valutazione della sicurezza dei margini e per progettare, se necessario, una loro efficace protezione. La letteratura tecnica internazionale, costituita da pubblicazioni, rapporti di ricerca, manuali, linee guida e normative, di contro include vari criteri di valutazione e soluzioni schematiche per i problemi che possono incontrarsi. Il presente lavoro fa una sintesi ragionata delle indicazioni riportate in buona parte di tali documenti ed ha l’obiettivo di fornire dei suggerimenti che possono essere un valido aiuto per il tecnico incaricato dello studio della protezione dei margini stradali. Oltre a ciò si includono i risultati di studi appositamente svolti dall’autore. Nella prima parte del lavoro, di tipo generale, si mostra dapprima la valenza del problema delle fuoriuscite con riferimento sia ai dati ISTAT sia ai dati raccolti con un’apposita indagine su due tratti autostradali. Con riferimento alla prima fonte, la quale include soltanto gli incidenti ove si sono avuti decessi e feriti ospedalizzati, si ha che questa tipologia di incidenti è preceduta come numerosità in maniera significativa soltanto dal tamponamento e dallo scontro fronto laterale. Riguardo alla pericolosità essa invece è preceduto in termini di vittime soltanto dallo scontro fronto-laterale. Le strade più pericolose nei riguardi delle fuoriuscite sono quelle provinciali e sono seguite in ordine da quelle comunali extraurbane, da quelle statali, dalle autostrade e poi infine da quelle urbane. L’indagine relativa invece ai due tratti autostradali, la quale include tutti gli incidenti rilevati dalle Forze dell’Ordine, ha mostrato invece che le fuoriuscite ammontano a circa il 44% del totale degli incidenti e che esse non sono le più pericolose. Dopo l’esame della pericolosità del di questa tipologia di incidenti segue un’elencazione di tutti i possibili ostacoli da considerare nella valutazione della sicurezza dei margini, unita ad una stima del danno medio di ogni impatto rispetto a quello che si ha nel caso delle barriere di sicurezza. Tali valori sono molto utili nel processo di valutazione della convenienza di un sistema di protezione. Successivamente a ciò si riportano le indicazioni reperite in letteratura sulle distanze di sicurezza a cui devono trovarsi gli ostacoli per non necessitare di protezione e si fornisce un criterio per definire queste ultime in funzione della pericolosità dell’ostacolo. L’esposizione prosegue poi con una disamina delle classi di contenimento delle barriere di sicurezza richieste in varie nazioni. Queste vengono confrontate applicandole ad una situazione reale per la quale è stata stimata la funzione di distribuzione dell’energia dei veicoli in fuoriuscita. Oltre ciò si illustra l’applicazione della procedura benefici-costi per la scelta della barriera di sicurezza. Dopo questa parte di tipo generale ne segue una più applicativa che tratta l’estensione minima delle barriere di sicurezza in relazione alle caratteristiche dell’ostacolo, la distanza tra barriera ed ostacoli, la larghezza del supporto alla barriera, le interruzioni delle barriere, le azioni trasferite alle pareti nel caso di impatto, gli spartitraffico, i bordi delle opere d’arte, gli svincoli e gli accessi. Per ognuno di questi argomenti sono riportate e confrontate le indicazioni e le soluzioni tipologiche presenti in parte della letteratura tecnica internazionale.

The study of travellers behaviour in ATIS (Advanced Travellers Information Systems) contexts is a crucial task in order to properly simulate phenomena like as the compliance with the information, the route choice in presence of information, etc. A correct simulation of these phenomena is crucial in appraising ATIS options. Observations of travellers behaviours are often made with reference to simulated environments. SP (Stated Preferences) techniques are generally applied. In literature two main types of tools for SP experiments under ATIS are found: driving-simulators (DSs) and travel-simulators (TSs). Both methods are computer-based. DSs are characterised by a greater realism, provided that the respondents are asked to drive in order to implement their travel choices, as it happens in the real world. In TSs, travel choices are entered after the description of the options and characteristics is presented, without any driving. TSs compensate some lack of realism with a minor cost and with less burden for the respondents, thus allowing for many more trials by the same respondent. In this work both the tools have been employed in order to collect data for analyses on travellers’ behaviours in ATIS contexts. The same network has been simulated by using both the tools and two very similar experiments have been carried out. The respondents’ reactions to the same information dispatched in the two environments have been registered and analysed. Results are here discussed in order to: compare the observations from the two experiments; verify the internal consistency of the collected data; discuss the peculiarities of the two data-collecting tool ATIS, Compliance, Route Choice, Travel Simulator, Driving Simulator, Stated Preferences

Among ITS (Intelligent Transportation Systems) applications, a relevant interest has been devoted in recent years to ATIS (Advanced Travellers Information Systems). The prediction of travellers’ route choice, in a context in which they are provided with information by different systems (VMS; route guidance; in car navigation systems), includes the study of travellers’ compliance. In order to be effective, ATIS require appropriate levels of travellers’ compliance with the dispatched information (Bifulco et al., 2007). Compliance and accuracy of information systems are implicitly related. It is worth noting that an appropriate level of compliance (as well as of familiarity with the technologically dispatched information) is reached also (maybe mainly) with respect to recurrent conditions. Accuracy of information systems can be evaluated by respondent, on the base of the discrepancy between suggestions received by ATIS, and experienced travel times. Putting in place accurate ATIS is not only due to technological matters but also (and mainly) to modelling issues, mainly related to the fact that the ATIS-information design problem is, in recurrent traffic conditions and for dynamic and predictive ATIS, a typical anticipatory-route-guidance problem (Crittin et al., 2001). The design of an accurate information system is obtained not only by advanced technologies but also with complex implementations of iterative procedures. In order to reach highaccuracy performances, it is required the availability of proper simulation models where the effect of the information accuracy on the compliance with information is explicitly and endogenously modelled. In order to study and model the travellers’ response to the information systems, different approaches have been adopted for data acquisition. In particular, the difficulty in gathering data from the real world has induced many researchers to adopt the Stated Preferences approach. Several researches have carried out experiments by adopting computer-based tools (travel simulators) or by designing a virtual reality in a driving simulator (Klee et al.); in both cases the main advantage is identified by the possibility to control the experiment variables (e.g. actual costs; accuracy of information; the set of choices characteristics, etc.). Different kind of models in ATIS’ contexts have been already dealt with (Avineri, et al., 2003; Ben-Akiva et al. 1991; Emmerink et al., 1994; Ettema et al., 2006; Van der Mede et al., 1996), and the most common adopted simulators have been travel simulators; nevertheless, some studies have also been made by adopting driving simulators (Chang, H.L. et al., 2009; Katsikopoulos et al, 2000-2002). In a driving simulator (characterized by very expensive technologies) the experiment designed is more complicated with respect to the travel simulator; besides, the experiment takes more time with respect to the travel simulator. However, the main advantage of the experiments made by driving simulators is that the virtual and immersive reality induces a more realistic behaviour of the respondents. Driving simulators are particularly suitable when the focus of the experiments is on driving choices and are very efficient also in reproducing the mental workload induced by driving. Rarely, results obtained by driving simulator and travel simulator are compared (Bonsall et al.,2000; Katsikopoulos et al., 2000). This, in order to improve the design of information (in terms of accuracy and quality), on the base of respondents’ behaviour, and by identifying the biases introduced in the experiments (Koutsopoulos et al., 1995). In our work, two experiments have been made by adopting both a driving simulator (route choice virtual simulator) and a travel simulator (SP Platform- Bifulco et al., 2009). In the experiment the respondents’ reaction to variable message signs has been studied and modelled. Respondents have been provided with the same kind of information (mixed information – prescriptive plus descriptive) and at the same levels of accuracy (respondents have been tested in different scenarios, each of them characterised by a different level of accuracy). Therefore the running experiments is the same: respondents are asked to repeatedly make their choices. By coupling the web-based and the driving-simulator-based experimental contexts, two main experimental strategies for observing drivers behaviours have also been coupled

In the paper, results from in-depth investigation of 1,092 run off the road (ROR) crashes on the motorway A16 (Italy) are presented. The research is aimed at pointing out risk factors that can address highway agencies and designers toward the selection of safety countermeasures aimed at reducing ROR crashes frequency and severity. Crash data were collected trough the analysis of police crash reports and relate to the period 2001-2005. Basing on police and hospital reports, each crash was categorized in six injury levels. To determine whether a specific crash pattern of the analysis group was significantly different from that of the control group, the Chi Squared (χ2) test with Yates’ correction was performed. Severity of motorcycle crashes was significantly higher than severity of other vehicle types. In adverse environmental conditions (night time and wet pavement), crash severity was lower than in favourable conditions. Crashes against ditches, walls, foreslopes, and backslopes were more severe than crashes against roadside steel safety barriers. Comparison between severity of crashes against longitudinal safety barriers and their blunt end terminals showed a dramatic increase in crash severity against the terminals. Thrie-beam roadside barriers that meet EN 1317 performance criteria showed a smaller crash severity and a better performance compared to older W-beam roadside barriers. Median New Jersey concrete barriers, compared to median steel safety barriers, showed greater crash severity and greater proportion of rollovers, not counterbalanced by a significant better behaviour in relation to penetration and override. run-off-the-road crashes, injury levels, concrete New Jersey safety barriers, steel safety barriers, blunt end terminals

The paper investigated drivers’ speed behaviour in a section of a rural highway crossing a small urban community in the existing scenario without any traffic calming device and in two different design scenarios with traffic calming in the urban community. Two gateways and four integrative traffic calming devices along the route within the urban area were tested. The gateways were aimed at slowing down the vehicles entering in the built-up area, while the traffic alming devices were aimed at complementing the gateway effect inside the built-up area. Two design options were tested: first option (alt1) is a combination of low cost measures, whereas the second option (alt2) is more expensive as includes a chicane and requires land acquisition. Drivers’ behaviour was investigated by means of a driving simulator experiment. The VERA dynamicdriving simulator operating at the TEST Road Safety Laboratory located in Naples (Italy) was used. Simulation results were validated by the comparison of speed behaviour in the real world and in the driving simulator, in the scenario without traffic calming. Analysis of the driving simulator experiment results was performed using two different approaches: (a) explorative description of data by cluster analysis; (b) inferential procedures about population using statistical tests. Cluster analysis was carried out in order to test if the drivers’ speed behaviour in the different design alternatives was substantially different. Statistical tests were performed in order to verify if speeds in specific sections were significantly different. Cluster analysis looked at speed profiles, whereas statistical tests looked at speed data in specific points. The obtained results showed a different behaviour of drivers approaching the urban community in the existing scenario and in the design scenarios. In the south direction, mean speed reduction ranging between 16 and 17 km/h, with 5% level of significance, was observed. In the north direction, mean speed reduction equal to 11 km/h, with 10% level of significance, was observed. Differences between the two design alternatives were not statistically significant. Along the urban community, a statistically significant mean speed reduction ranging between 9 and 15 km/h was observed in the south direction. In the north direction, speed reduction was not statistically significant. Overall, combined results of cluster analysis and statistical tests showed that the treatments were more effective in the direction with higher speeds in the base scenario.

This study was intended to assess what happens during the collision of an articulated trucks against an elastic wall, in terms of interaction forces and stress resultants at the lower edge of the wall. The research was carried out through a numerical approach and includes three parts. In the first part, a brief description of the main characteristics of the FE model is proposed. Moreover, the comparisons of full scale and simulated outputs of the collisions used for its validation are described. The obtained results demonstrate that the modeling process is accurate and that the FE model is reliable in a wide range of impact conditions. The second part is aimed at clarifying what happens during the impact. The results obtained clearly show that the interaction forces and stress resultants at the lower edge of the wall are affected in a meaningful manner much more by the impact angle than by the transversal kinetic energy. The last part defines a simple procedure useful to estimate the overall interaction force and the maximum bending moment at the lower edge of the wall for a very wide range of impact conditions. The tests performed on the procedure show a very good agreement between estimated and calculated values.

The paper investigated drivers’ speed behavior in rural highways crossing small urban communities both without any gateway and traffic calming device and with different configurations of gateway and traffic calming along the urban environment. Speeds in entrance to small urban areas were collected in Italy in 6 rural road sections. The site with the greater operating speeds was selected as the design site. Two gateways and four integrative traffic calming devices along the route within the urban area were designed. The gateways are aimed at slowing down the vehicles entering in the built-up area, while the traffic calming devices are aimed at complementing the gateway effect. Two gateway design options have been proposed: first option is combination of low cost and fast implementation measures, whereas the second option is more expensive since includes an horizontal deflections and requires land acquisition. Drivers’ speed behavior in the design alternatives was assessed in a dynamic driving simulator. Both gateway treatments were highly effective in reducing speed. In the gateway, mean speed reductions were equal ranged between 11 and 17 km/h. In the village midpoint, both means and standard deviations of the speed distribution showed a reduction. Mean speed reductions ranged between 9 and 14 km/h. Overall, the design alternative 2 showed better results and is suggested for implementation.

Road roughness represents a key parameter in pavement management systems as it affects driver’s riding comfort, pavement performance and Vehicle Operating Costs. Ride quality is related to in-vehicle vibration that, in turn, is dependent on the level of road roughness, on the speed chosen by the driver and on the inertial and mechanical characteristics of the vehicles. Several studies have highlighted that, under certain conditions, driver may be induced to vary his speed in order to reach an acceptable in-vehicle vibration level according to his subjective exposure threshold. In this paper, a further contribution on this issue is presented. A dynamic driving simulator (DDS) employing a real car fixed on a 6 degrees of freedom motion platform is currently operating at the TEST Laboratory in Naples. The DDS system is able to reproduce most of the accelerations the occupants feel, in particular those arising from turning and braking maneuvers and from dynamic interaction with pavement surface singular irregularities. A team of researchers from University of Naples “Federico II”, Second University of Naples, University of Cassino (and the Oktal Company) have improved the system allowing the implementation of a module simulating vehicle vibrations induced by distributed irregularities. In this paper, the development of the vibration simulation module and the results from preliminary experimental calibration procedures are briefly reported. The initial outcomes of the performed tests seem to fairly agree with similar published results derived from technical literature

The containment capacity of a road safety barrier is usually assessed by full-scale crash tests on level terrain. Unfortunately, this condition almost never corresponds to real situations because of the presence of steep embankments foreslope adjacent to the backside of guardrail posts. The presence of the foreslope adjacent to the posts both reduces the lateral load capacity of these - the “resistance” effect - and leads to the wheels penetration in it - the “geometrical” effect-. This paper describes a research aimed at evaluating the aforementioned effects of a 3:2 foreslope near to the backside of the posts of a real H1 (according to the EN 1317 standard) safety barrier which was successfully tested at level. The research has been carried out through a combined experimental and numerical approach. The crash test FE simulations have been performed with the Ls-Dyna 970 code version MPP. The results obtained put in evidence that the containment capacity of the considered barrier is affected only by the “resistance” effect, that is the reduction in the lateral load capacity of posts. The failure in the containment happens when the lateral load capacity of posts halves. This occurs for every distance from the top of the slope to the backside of the post.

The effectiveness of the FEM (Finite element method) approach to improve crashworthiness, both from the vehicle viewpoint and from the road safety hardware one has been plainly demonstrated in literature. Of course, this is possible only when models calibrated in a wide range of impact conditions are available. In this work, a multipurpose finite element model of a light weight passenger car is presented. The model has been set up through an extensive comparison between full-scale and simulated outputs of four different experiments: the frontal and oblique collisions against a concrete wall and the impacts against two types of steel barrier with different containment energy level (127kJ and 724kJ). The differences between these impacts are related to (i) the stiffness of the safety devices and to (ii) the height where the vehicle collides against the barriers. Therefore, the considered situations are representative of a wide range of impact conditions The fundamental steps of the modelling process will be described along with all the particulars needed to reproduce the four full scale tests. Data comparison between full-scale and FE simulation concerns time histories of longitudinal and transversal acceleration of CG’s vehicle, ASI, THIV, PHD, pitch and roll angle, velocity variation in the vehicle direction and residual displacements of the barrier.

The effectiveness of FEM (Finite element method) approach to improve crashworthiness, both from vehicle viewpoint and from road safety hardware one has been plainly demonstrated in literature. Of course, this is possible only when models calibrated in a wide range of impact conditions are available. In this work, a multipurpose finite element model of a light weight passenger car is presented. The model has been set up through an extensive comparison between full-scale and simulated outputs of four different experiments: the frontal and oblique collisions against a concrete wall and the impacts against two types of steel barrier with different containment energy level (127kJ and 724kJ). The differences between these impacts are related to (i) the stiffness of the safety devices and to (ii) the height where the vehicle collides against the barriers. Therefore, the considered situations are representative of a wide range of impact conditions The fundamental steps of the modelling process will be described along with all the particulars needed to reproduce the four full scale tests. Data comparison between full-scale and FE simulation concerns time histories of longitudinal and transversal acceleration of CG’s vehicle, ASI, THIV, PHD, pitch and roll angle, velocity variation in the vehicle direction and residual displacements of the barrier. The excellent agreement attained when simulating the abovementioned impacts, characterized by noticeably different nature, demonstrates that the modelling processes of vehicle and devices were accurate and that, in particular, the FE model of the passenger car is suitable for a wide range of impact conditions. As a conclusion, the validated model is reliable to foresee the impact behaviour without needing expensive crash tests

The sight distance available on existing roads is very often lower than the stopping sight distance needed to avoid the collision with standing obstacles in the travelled way. When this occurs many rear-end crashes can happen because each follower could not see his/her leader. The investments needed to increase the sight distance to the value arising from the actual speed of the vehicles are usually very high. Due to budget constraints road agencies have to select the road segments to improve by estimating their safety performance. This activity is not an easy task. The most useful approach to address this type of problem is to use a microsimulation traffic model, which has to consider roadway configuration, sight distance, roadway surface condition, braking lights, human behaviour, etc. With this type of tool it would be possible to define the number of collisions or loosing control vehicles, their corresponding speed, the number of vehicle at collision “risk” in the queue, etc. In this paper the structure of a microsimulation model tacking into account most of the influencing factors is presented. It has been conceived with the aim to reproduce what happens in situations where the sight distance is reduced. The first part of the paper concerns the description of the modules in which the model is organized. The second part presents an application to a road segment where a standing obstacle exists in a curve and the sight distance is limited by a retaining wall. This situation has been compared with a similar road segment where the sight distance complies with the Italian Standard. The results obtained show the higher is the flow rate the lower are the rear-end crashes and loosing control vehicles. This is due to the fact that for high flow rate the vehicles are slower and a very high interaction exists among them, so that the braking lights of the leaders suggest to the followers to adopt a prudential behaviour.

Longitudinal safety barriers are tested in order to assess the safety barriers containment capacity and the vehicle occupant impact severity. In the EN standards, the occupant impact severity is evaluated with the same test (TB11) for all the classes of barrier: a 900 kg car colliding with impact speed equal to 100 Km/h and impact angle equal to 20°. Considering that real world impact conditions may be substantially different, at least two questions arise: 1. Which is the distribution of passenger cars kinetic impact energy for different type of roads and which is the relative position of the conventional test? 2. Are the values of Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV) and Post-impact Head Deceleration (PHD) obtained in the conventional test TB11 representative for real world impact conditions? The “correct” answer to these questions requires a very expensive research program. This because a huge number of accident reports has to be collected and each accident event has to be reconstructed, furthermore many computer crash simulations have to be performed. In order to get a “preliminary” problem assessment, a study has been carried out performing an accident analysis and many crash simulation in different impacting conditions. The accident analysis has been carried out by the examination of 160 police run off the road accident reports on a rural dual carriageway road, integrated with the inspection of accident sites. Many accident parameters have been evaluated and distribution probabilities of impact velocity, impact angle and vehicle mass have been drawn. The real world impact conditions obtained have been used as input for the crash simulation of a passenger car against a longitudinal safety barrier. Impact simulations have been carried out by non-linear dynamic finite element analysis performed with the software LS-Dyna. The finite element model used for the vehicle is the result of an extensive modeling activity and is very capable to represent the crash dynamics and consequences. Collision outcomes in terms of THIV, PHD and ASI have been evaluated for each impact condition and, by combining the impact condition distributions with these results, the distributions of the impact severity indices have been assessed. The study carried out show that the probability of outcomes greater than the ones of the TB 11 are equal to 26% for ASI, and 34% for THIV and PHD. According to the results of the study, passenger cars crash test conditions more representative of real world impacts, on motorways and on rural dual carriageway roads, would be: - Impact speed = 130 km/h; - Impact angle = 20 degrees; - Vehicle mass = 1500 kg. Such impact conditions would represent the ninetieth percentile of cars kinetic transversal impact energy. Moreover, with reference to the rigid wall fixed to the ground used in the simulations, they give rise to ASI, THIV and PHD values more severe than eighty-five percent of real world run off the road accidents. The previous results show that the conditions proposed by the standard could be not conservative in Italy. They have to be intended, however, as preliminaries and stressing the need of a more in depth, and public funded, research program.

Longitudinal safety barriers are tested in order to assess the safety barriers containment capacity and the vehicle occupant impact severity. In the EN standards, the occupant impact severity is evaluated with the same test (TB11) for all the classes of barrier: a 900 kg car colliding with impact speed equal to 100 Km/h and impact angle equal to 20°. Considering that real world impact conditions may be substantially different, at least two questions arise: 1. Which is the distribution of passenger cars kinetic impact energy for different type of roads and which is the relative position of the conventional test? 2. Are the values of Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV) and Post-impact Head Deceleration (PHD) obtained in the conventional test TB11 representative for real world impact conditions? The “correct” answer to these questions requires a very expensive research program. This because a huge number of accident reports has to be collected and each accident events has to be reconstructed, furthermore many computer crash simulations have to be performed. In order to get a “preliminary” problem assessment, a study has been carried out performing an accident analysis and many crash simulation in different impacting conditions. The accident analysis has been carried out by the examination of 160 police run off the road accident reports on a rural dual carriageway road, integrated with the inspection of accident sites. Many accident parameters have been evaluated and distribution probabilities of impact velocity, impact angle and vehicle mass have been drawn. The real world impact conditions obtained have been used as input for the crash simulation of a passenger car against a longitudinal safety barrier. Impact simulations have been carried out by non-linear dynamic finite element analysis performed with the software LS-Dyna. The finite element model used for the vehicle is the result of an extensive modeling activity and is very capable to represent the crash dynamics and consequences. Collision outcomes in terms of THIV, PHD and ASI have been evaluated for each impact condition and, by combining the impact condition distributions with these results, the distributions of the impact severity indices have been assessed. The study carried out show that the probability of outcomes greater than the ones of the TB 11 are equal to 26% for ASI, and 34% for THIV and PHD. According to the results of the study, passenger cars crash test conditions more representative of real world impacts, on motorways and on rural dual carriageway roads, would be:  Impact speed = 130 km/h;  Impact angle = 20 degrees;  Vehicle mass = 1500 kg. Such impact conditions would represent the ninetieth percentile of cars kinetic transversal impact energy. Moreover, with reference to the rigid wall fixed to the ground used in the simulations, they give rise to ASI, THIV and PHD values more severe than eighty-five percent of real world run off the road accidents. The previous results show that the conditions proposed by the standard could be not conservative in Italy. They have to be intended, however, as preliminaries and stressing the need of a more in depth research program.

Le disposizioni normative hanno sostanzialmente contribuito ad un notevole progresso tecnologico delle barriere di sicurezza. D’altra parte, in Italia, esse sono generiche per quanto riguarda l’individuazione delle zone da proteggere e la scelta delle classi di barriera da impiegare è una procedura complessa che dipende da numerosi fattori specifici relativi al sito, alla strada ed al traffico che interessano l’intervento e che non sono presi in considerazione nei criteri normativi. Al fine di migliorare le conoscenze relative al comportamento delle barriere di sicurezza e definire delle procedure analitiche per ottimizzare le scelte relative alla messa in sicurezza dei margini si sono effettuate delle analisi di incidentalità, delle analisi agli elementi finiti sul comportamento delle barriere di sicurezza e si è definita una procedura basata sull’analisi benefici/costi per la scelta delle classi di barriera.