Francesca La Torre

Calibration of the Highway Safety Manual's Accident Prediction Model for Italian Secondary Road Network

The forthcoming first edition of the Highway Safety Manual (HSM) will introduce safety predictive models both for road segments and intersections. A key issue for allowing HSM to become a standard for road owners and managers worldwide is the transferability of the predictive models to different networks. The application of the calibration procedure of the HSM model to different countries has been evaluated, with all practical and potential application problems outlined. In this study, the calibration procedure of the HSM model has been applied to the road network of the Italian province of Arezzo to evaluate the effective transferability of this methodology to a region characterized by a different environment and different road characteristics, driver behavior, and crash reporting systems than those on which the HSM models have been developed. The considered road network covers 1,300 km of rural two-lane highways located in the Arezzo province, and a 3-year (2002–2004) accident database has been used. The considerable difference between the road network of the Italian province of Arezzo and the one of Minnesota, for which the HSM model has been developed, causes practical application problems, mainly related to segmentation and over-estimation of curvature effects, which are discussed in the paper. Four approaches to define the calibration factor have been applied and discussed to determine the most effective one. Finally, this work points out the problems related to the identification of data needs and necessary treatments for the HSM model calibration and application.

Calibration of Mechanistic-Empirical Rutting Model for In-Service Pavements

Rutting is a major failure mode for flexible pavements. Pavement engineers have been trying to control and arrest the development of rutting for years. Many models are available to relate pavement rutting to design features, traffic loading, and climatic conditions. These models range from purely empirical to mechanistic models. Mechanistic-empirical models (the Asphalt Institute and Shell) were used to predict the development of rutting for 61 Long-Term Pavement Performance (LTPP) test sections. The rutting damage, calculated using these models, did not appear to be a good predictor of the observed rutting depth. A new rutting model was developed and calibrated using the data from the 61 LTPP sections. The model accounts for the plastic deformation in all pavement layers and allows the use of actual axle load and type, rather than the equivalent single axle load, in characterizing traffic.

Transferability of the Highway Safety Manual Freeway Model to the Italian Motorway Network

The currently available release of the AASHTO Highway Safety Manual (HSM) does not include a model for freeways and interchanges. NCHRP Project 17–45 has recently developed specific crash prediction models for this type of infrastructure. Key to making the HSM a standard for road owners and managers worldwide is the transferability of prediction models to different networks. An extensive study conducted on the primary Italian motorway network evaluated the potential issues in application of this methodology to a network characterized by environmental conditions, road characteristics, driver attitudes, and crash reporting systems different from those for which the HSM models were developed. The freeway network considered in this study, approximately 6,700 km long, was represented by 56 freeway sections characterized by an average length of about 12.5 km, covering 700 km of freeway distributed throughout Italy. Four calibration factors were obtained for freeway segments, according to crash severity and type, and two calibration factors were obtained for speed-change lanes, according to crash severity. The results show a good transferability of the analyzed models to the Italian network, especially the freeway models for fatal and injury crashes, although a tendency to underestimate locations of high crash frequency was observed. Some improvements could be made concerning variable calibration factors within the data sets or local calibrations for crash modification factors. Improved localization of the crash data on the Italian road network needs to be highlighted, mainly for speed-change lanes.

CORRELATION BETWEEN LONGITUDINAL ROUGHNESS AND USER PERCEPTION IN URBAN AREAS

Pavement management in urban areas requires the identification of appropriate roughness indicators and of related acceptability thresholds. The use of the international roughness index (IRI) is not suitable for urban areas owing to a number of problems. The available length of homogeneous sections is often much shorter than the typical 320 m used in the World Bank experiment that led to the IRI classification. The speed is considerably lower than the 80 km/h considered for the IRI quarter car model. Also, the type of paving materials used in urban areas can be considerably different than the ones used in rural areas, resulting in a different type of roughness (as in the case of stone pavements). Furthermore, the acceptability levels in urban areas need to be defined according to the different perception of the user and additional environmental constraints. Within the Interazione Ambiente Sicurezza nel Progetto delle Infrastrutture Viarie project funded by the Italian Research and University Ministry, an extensive study has been conducted to define a roughness index suitable to represent urban streets and to identify acceptability thresholds. For this purpose, a number of urban sections with different pavement surfacing and age have been identified, and on each section the profile has been measured. To identify user perception toward the different pavement conditions, a rating procedure has been defined, and a panel rating has been performed on each section.

Influence of the lighting system on the driver's behavior in road tunnels: A driving simulator study

ABSTRACT The tunnel lighting system is an important factor affecting driving safety, but it also represents the most expensive operative cost of a tunnel. Conventional tunnel lighting systems have been progressively replaced by LED lighting systems. This technology is spreading fast because of its low energy consumption and the high durability combined with low maintenance requirement. Aim of this research was to assess, by means of driving simulator experimentation, the impact of the LED lighting system on traffic safety. The driver performance approaching inside and exiting LED lighted tunnels was analyzed and compared to the behavior maintained in tunnels illuminated with a traditional system, in normal and in critical conditions. Thirty-one young participants drove through two different virtual scenarios while data on their speed, lateral position, and reaction in front of a sudden obstacle in the carriageway were collected. A statistically significant difference was revealed as a function of the type of lighting; simulated LED lights often induced a better driving behavior under some aspects. The motorists were able to perceive in advance the critical situation and the consequent maneuvers were carried out in a more effective way. Moreover, drivers kept better their lateral trajectory control in transition areas.

Evaluation of mechanical performance of cement–bitumen-treated materials through laboratory and in-situ testing

Nowadays, cold recycling is considered as a common road construction/maintenance technique and no longer as an alternative technique to the traditional ones. The difficulties in simulating the production and construction processes in laboratory have led researchers to practise full-scale testing of mixtures. This paper presents a comprehensive evaluation of the mechanical performance of a cement–bitumen-treated materials (CBTMs) containing 80% of reclaimed asphalt. After a preliminary mix design, the mixture was produced in a mix plant and laid down on two trial sections with different layer thicknesses (15 and 20 cm) over a homogeneous subgrade. The mixture was sampled before laying, compacted and characterised through indirect tensile test and indirect tensile stiffness modulus test. The same tests were carried out on cores taken from the trial sections. Light weight deflectometer and falling weight deflectometer surveys were performed on the trial sections to evaluate the performances of the CBTMs.

Evaluation of the vehicle/safety barrier/sign support interaction by means of FEM simulations

This paper deals with the evaluation of the interaction between a safety barrier and a variable message sign (VMS) that is placed very close to the carriageways in order to reduce the length of the arm above the carriageways. The two issues addressed are the structural response of the VMS, in order to ensure that the structure will not fail under the impact of a heavy goods vehicle (HGV), and the effects of the secondary impact that occurs when the barrier or the vehicle hits the VMS structure. These issues have been analysed both in terms of overall performance of the barrier and of the resulting effects on the HGV itself. As a result, the minimum distance between the front of the barrier and the VMS support structure that will enable to have a performance fully compatible with the requirements of EN1317-2:2010 has been defined for a specific barrier/VMS system.