Mariano Pernetti

Perceptual Measures to Influence Operating Speeds and Reduce Crashes at Rural Intersections: Driving Simulator Experiment

The aim of this paper is to investigate, by means of a dynamic driving simulator experiment, the behavior of road users at rural intersections in relation to perceptual measures designed for increasing hazard detection. In the experiment 10 configurations of tangents were tested: Alt1, base tangent; Alt2, four-leg base intersection; Alt3, intersection with reduced sight distance; and Alt4 through Alt10, intersections with perceptual treatments. The Virtual Environment for Road Safety high-fidelity dynamic-driving simulator, operating at the Technology Environment Safety Transport Road Safety Laboratory located in Naples, Italy, was used. Analysis of the results used two approaches: (a) explorative description of data by cluster analysis and (b) inferential procedures about population using statistical tests. Results showed that the speed behavior in the tangents was significantly affected by the presence of the intersections and by the perceptual treatments. Intersections without perceptual treatments significantly affected driver speeds in the 250 m preceding the intersection. Perceptual treatments helped the driver to detect the intersection earlier and to slow down. Dragon teeth markings, colored intersection area, and raised median island performed better than the other perceptual treatments. They produced significant average speed reduction in the 150 m preceding the intersection ranging between 16 km/h and 23 km/h. Study results support real-world implementation of perceptual measures in rural intersections because they are low-cost, fast implementation measures with a high potential to be cost-effective.

HEAVY-GOODS VEHICLE COLLISIONS WITH STEEL ROAD SAFETY BARRIERS: COMBINED INFLUENCES OF POSITION OF CENTER OF MASS AND TIRE-PAVEMENT FRICTION

Vehicles that collide with highway safety features do not always produce the same effects. The outcome for each vehicle that collides with a feature will be different, depending greatly not only on its mass, velocity, and impact angle but also on the position of its center of mass and on the tire-pavement friction. The ways in which barrier and striking vehicle behaviors are affected by changes in the position of the center of mass and in the tire-pavement side friction were analyzed to identify the most dangerous loading systems. Toward this aim numerous simulations of a collision of a truck against a steel road safety barrier were carried out through nonlinear, dynamic finite-element analysis. The results obtained demonstrate that the position of the center of mass is of greater consequence in collisions in which the impact energy is close to the maximum barrier containment capacity and under conditions that favor friction. The longitudinal position of the center of mass has a large impact on the risk that the vehicle will pass over the barrier or roll over. If it is in the back, the most common loading system, the risk of passing over the barrier is rather limited compared with the risk of rolling over. As the position of the center of mass is pushed forward, the risk of rolling over is reduced but the risk of passing over the barrier increases. If the height of the center of mass increases, the rollover risk is higher, but a higher center of mass does not significantly influence displacement and the risk of passing over the barrier.

Comparison of Collisions of Rigid Trucks and Articulated Trucks Against Road Safety Barriers

Heavy vehicles used for road transport are essentially rigid trucks, rigid trucks with trailers, and articulated trucks. A collision of such a vehicle against a safety barrier has different outcomes, depending on the vehicle characteristics, even when the impact energy (Ie) is the same. The factors responsible for the different behavior of rigid and articulated trucks during collision are addressed. The study, carried out by computer simulation, was divided into three parts. The first part compared the overall behavior of the two types of vehicles during collisions to detect the most responsible factors. In the second phase, the single features that characterize each type of vehicle were tested. The third phase tried to define a relationship between the two types of vehicles. Results from Tests TB81 and TB71, established by the European Committee for Standardization 1317, were compared. The results show that a collision of an articulated truck is less severe than one of a rigid truck because of greater length, suspension stiffness, inertia, and configuration. However, the difference in behavior depends on kinetic Ie and side-friction coefficient (SFC). Four analytical expressions were found that relate Ies producing the same maximum transversal displacements or vehicle roll angle for the two types of vehicles. The study concerning the European tests on safety barriers shows that a hierarchy exists between them and it depends on the SFC.