3D GIS BASED EVALUATION OF THE AVAILABLE SIGHT DISTANCE TO ASSESS SAFETY OF URBAN ROADS

The available sight distance (ASD) in front of the driver to detect possible conflicts with unexpected obstacles is fundamental for traffic safety. In the last 20 years, road design software (RDS) has been continuously updated with dedicated modules to estimate ASD, thus assessing the quality of project from a safety point of view. Unfortunately, the evaluation of ASD still represents an issue in the case of existing road, and the object of discussion in the research community. To avoid problems related to the limitation associated with the use of digital terrain models typically employed in RDS, the Geographic Information Systems (GIS) software can use digital surface models (DSM) which are more flexible in the modelling of sight obstruction due to vegetation, street furniture, and vertical surfaces largely diffused in urbanized areas. The paper deals with the evaluation of GIS in the estimation of ASD in a typical urban road where the density of sight obstruction along the roadside is relatively high. The work explores the case study of a collector road in the city of Turin (Italy). Results confirm the potentiality of GIS software in capturing the complex morphology of the urban environment, thus confirming that GIS could become an important analysis tool for road engineers in the field of road safety. The investigation here described is part of the Pro-VISION Project (funded in 2014 by the Regione Piemonte, Italy)

Stress dependent behaviour of unbound layers of unselected construction and demolition waste aggregates by lightweight deflectometer tests

The use of construction and demolition waste (CDW) aggregates in unbound road pavement layers is increasing. However, the lack of data on performance in the field has spurred this investigation into their in-situ properties. A lightweight deflectometer (LWD) is a fast and simulative testing device for estimating the elastic modulus of unbound pavement layers. A field test pit was built to run LWD measurements on an unbound subbase layer containing CDW aggregates compacted at different energy levels. To assess their stress-strain non-linear behaviour, several LWD drops were performed on the same location by varying (i) the loading mass, (ii) the drop height, and (iii) the plate diameter. A stress-hardening behaviour of in-situ CDW aggregates was observed, consistent with the stress dependent evolution of resilient modulus of granular material commonly recorded in laboratory tests. The LWD modulus was found to be dependent on the level of compaction energy but also sensitive to the mechanical response of the layer below. The outcomes at this test pit suggest it would be wise to consider the rational evaluation of the in-field stress dependent behaviour of unbound CDW granular materials at both the design stage and when devising quality acceptance procedures. Nonetheless, to have a comprehensive interpretation of LWD results a greater uniformity of material properties and a stronger control of construction procedures will be desired, especially when heterogenous materials such as CDW aggregates are investigated

Estimating the Available Sight Distance in the Urban Environment by GIS and Numerical Computing Codes

The available sight distance (ASD) is that part of the roadway ahead which is visible to the driver, and should be of sufficient length to allow a vehicle traveling at the designated speed to stop before reaching a stationary object in its path. It is fundamental in assessing road safety of a project or on an existing road section. Unfortunately, an accurate estimation of the available sight distance is still an issue on existing roads, above all due to the lack of information regarding the as-built condition of the infrastructure. Today, the geomatics field already offers different solutions for collecting 3D information about environments at different scales, integrating multiple sensors, but the main issue regarding existing mobile mapping systems (MMSs) is their high cost. The first part of this research focused on the use of a low-cost MMS as an alternative for obtaining 3D information about infrastructure. The obtained model can be exploited as input data of specific algorithms, both on a GIS platform and in a numerical computing environment to estimate ASD on a typical urban road. The aim of the investigation was to compare the performances of the two approaches used to evaluate the ASD, capturing the complex morphology of the urban environment

Back-propagation neural networks and generalized linear mixed models to investigate vehicular flow and weather data relationships with crash severity in urban road segments

The paper deals with the identification of variables and models that can explain why a certain Severity Level (SL) may be expected in the event of a certain type of crash at a specific point of an urban road network. Two official crash records, a weather database, a traffic data source, and information on the characteristics of the investigated urban road segments of Turin (Italy) for the seven years from 2006 to 2012 were used. Examination of the full database of 47,592 crash events, including property damage only crashes, reveals 9,785 injury crashes occurring along road segments only. Of these, 1,621 were found to be associated with a dataset of traffic flows aggregated in 5 minutes for the 35 minutes across each crash event, and to weather data recorded by the official weather station of Turin. Two different approaches, a back-propagation neural network model and a generalized linear mixed model were used. Results show the impact of flow and other variables on the SL that may characterize a crash; differences in the significant variables and performance of the two modelling approaches are also commented on in the manuscript

Longitudinal and Transversal Driver Behaviour with Innovative Horizontal Markings Along Curved Motorway On Ramps and Terminals

The manuscript presents a driving simulation study on the effectiveness of two innovative horizontal marking designs (in comparison with the conventional marking) along acceleration ramps and reverse and continue terminals on curved motorway sections. Longitudinal and transversal behavioural data were collected from forty-eight test drivers in response to variations in marking type, lighting conditions, and traffic-flow along the motorway. Although the innovative markings did not have a significant impact on speeds along continue terminals, they did have an impact on the lane gap and the standard deviation of lateral positions. Along the reverse terminal design type, their impact was evident on all the investigated longitudinal and transversal outcomes. This study proved that the perceptual techniques used by drivers engaged in speed and trajectory management along curved terminals are effective in promoting better driving performances

Traffic crash pattern modification as a result of a 30 km/h zone implementation. A case study in Turin (Italy)

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Investigation of Influential Variables to Predict Passing Rate at Short Passing Zones on Two-Lane Rural Highways

The passing zone (PZ) is that part of two-lane highways in which drivers can safely overtake slower vehicles. Several studies have presented passing rate models in the PZ. However, there is no model to predict the passing rate in PZs shorter than 350 m. Furthermore, the effect of variables such as lane width and the proportion of motorcycles on the passing rate were not investigated in previous works. This study assessed the effects of these variables on the passing rate and presents a prediction passing model for short PZs. Data were collected from seven PZs using a drone on three different two-lane rural highway segments in Iran. The results showed that the passing rate depends on the lane width, the absolute vertical grade, the flow rate in both directions, the directional split, the proportion of heavy vehicles in the subject direction, and the proportion of motorcycles in the subject direction. Short PZ length values did not have a significant effect on the passing rate. The passing capacity occurred at a flow rate of 680vehicle/h in both directions irrespective of the directional split

Vehicle movements in roundabouts

This article describes a research study that used a new method based on image processing for analyzing vehicle movements in traffic circles (roundabouts). The study had three stages: a field survey to collect vehicular flow images captured by video cameras; the processing of these images using a proprietary software (VeTRA—Vehicle Tracking for Roundabout Analysis); and the analysis of the collected data. The authors note that the software allows the automatic computation of the main variables necessary to rank and evaluate a generic roundabout: the entry/exit (E/E) matrix with classification of vehicles (e.g., heavy, light, and motorcycles), vehicle trajectories, and vehicular speed diagrams along the paths of the traffic circle. The processing system can overcome classic problems affecting image processing such as variable wind conditions, cloud cover, shadows, and obstructions. The authors manually compared data on entry and exits generated by VeTRA to those manually counted on the corresponding video images. They also present a case study of an existing roundabout in an urban Italian environment. The authors conclude that the software has a high capability of generating the E/E matrix and that the analysis of vehicular trajectories enable the accurate evaluation of driver behavior in the roundabout

Performance-based Re-use of Tunnel Muck as Granular Material for Subgrade and Sub-base Formation in Road Construction

Large volumes of muck are produced in the Alpine Region and bordering areas as a result of new road and railway construction. For example, in Austria every year approximately 32*10^6 Mg of muck are produced from tunnelling activities. In the near future, many other initiatives along the European corridors will lead to further construction activity, with an inevitable increase in the environmental problems related to the use or disposal of the muck generated. Therefore, there is a clear opportunity for the extensive re-use of muck due to the high demand for granular materials (about 3 billion tonnes in Europe, only 5% of which comes from recycling), the depletion of existing quarries (approximately 24,000 in Europe), and the environmental constraints preventing or delaying the opening of new quarries. In this scenario, a new approach to the re-use of muck is both necessary and timely. Although many typical defects deriving from its geological nature and/or from the extraction techniques employed may lead to its rejection as an aggregate, these same defects are of less importance in embankment, subgrade and sub-base construction in transportation infrastructures and, indeed, in most cases they can be mitigated by granular or chemical stabilization. The investigation described here embraces this philosophy. Starting from the chemical physical characterization of seven different mucks derived from tunnelling activities on the Italian side of the Alps, the paper aims to explore the potential benefits deriving from their re use as a construction material. The test methods used all adhere to prescriptive and performance based construction specifications. Notwithstanding the unfavourable geological origin of some of the considered materials, they all exhibited mechanical properties that would encourage their almost complete re-use in infrastructure construction projects