Alessandro Vitale

Comparing Safety at Signalized Intersections and Roundabouts Using Simulated Rear-End Conflicts

The safety implications of adopting roundabouts in place of conventional signalized intersections have not been adequately assessed. A microscopic simulation model was used to compare the pattern of traffic conflicts at roundabouts with conflicts for signalized intersections. Three indicators of safety performance were defined: (a) time to collision (TTC), (b) deceleration rate to avoid the crash (DRAC), and (c) crash potential index (CPI). For each indicator, traffic conflict profiles were obtained in terms of number of vehicles in conflict and number of conflicts per vehicle for selected directional maneuvers. The exposure time to conflict for each maneuver and vehicle was also determined. Twelve combinations of geometric and traffic attributes (traffic scenarios) were simulated over a 15-min period. The results suggested that roundabouts yield reduced exposure times to rear-end conflicts compared with signalized intersections. On average, signalized intersections also reflected increased number of vehicles in conflict and percentage of vehicles in conflict compared with roundabouts. This relationship was found to be independent of input volumes and pavement surface condition and applied consistently to all safety indicator measures (TTC, DRAC, and CPI).

Comparing Safety Performance Measures Obtained from Video Capture Data

Safety performance is evaluated by using measures obtained experimentally from a videotaping of traffic operations at an urban roundabout situated in Cosenza, Italy. Five different expressions of safety performance from the perspective of “rear-end” vehicle interactions include maximum deceleration rate to avoid a crash (DRAC), time-to-collision (TTC), proportion of stopping distance (PSD), time integrated time-to-collision (TIT), and crash potential index (CPI). Differences in safety performance are discussed with respect to the type of measure, traffic conditions, and variations in roundabout geometry. The results of this analysis suggest that safety performance is highly sensitive to the way it is measured; different measures can highlight different locations or geometric features of the roundabout as posing potential safety problems. This study underscores the usefulness of safety performance measures for providing meaningful experimental indicators of potential safety problems at roundabouts and how ...

Using Smartphones as a Tool to Capture Road Traffic Attributes

Road network management under critical conditions is achievable by adopting technologies that trace vehicles and capture unsafety events to provide users with real time traffic information. Most common approaches used to acquire vehicle tracking data are based on video image processing algorithms and satellite navigation systems. However, many studies are increasingly focused on the emerging smartphone technologies for tracking vehicles. The aim of this study is to present a procedure for acquiring vehicle tracking data from smartphone sensors, supporting managers of transportation systems to take effective decisions on their networks, especially in conjunction with special events and/or critical road safety issues.

Traffic data acquirement by unmanned aerial vehicle

ABSTRACT This paper presents a methodology aimed to acquire traffic flow data through the employment of unmanned aerial vehicles (UAVs). The study is focused on the determination of driving behavior parameters of road users and on the reconstruction of traffic flow Origin/Destination matrix. The methodology integrates UAV flights with video image processing technique, and the capability of geographic information systems, to represent spatiotemporal phenomena. In particular, analyzing different intersections, the attention of the authors is focused on users’ gap acceptance in a naturalistic drivers’ behavior condition (drivers are not influenced by the presence of instruments and operators on the roadway) and on the reconstruction of vehicle paths. Drivers’ level of aggressiveness is determined by understanding how drivers decide that a gap is crossable and, consequently, how their behavior is critical in relation to a moving stream of traffic with serious road safety implications. The results of these experiments highlight the usefulness of the UAVs technology, that combined with video processing technique allows the capture of real traffic conditions with a good level of accuracy.

The Use of Adaptive Traffic Signal Systems Based on Floating Car Data

This paper presents a simple concept which has not been, up to now, thoroughly explored in scientific research: the use of information coming from the network of Internet connected mobile devices (on vehicles) to regulate traffic light systems. Three large-scale changes are going to shape the future of transportation and could lead to the regulation of traffic signal system based on floating car data (FCD): (i) the implementation of Internet connected cars with global navigation satellite (GNSS) system receivers and the autonomous car revolution; (ii) the spreading of mobile cooperative Web 2.0 and the extension to connected vehicles; (iii) an increasing need for sustainability of transportation in terms of energy efficiency, traffic safety, and environmental issues. Up to now, the concept of floating car data (FCD) has only been extensively used to obtain traffic information and estimate traffic parameters. Traffic lights regulation based on FCD technology has not been fully researched since the implementation requires new ideas and algorithms. This paper intends to provide a seminal insight into the important issue of adaptive traffic light based on FCD by presenting ideas that can be useful to researchers and engineers in the long-term task of developing new algorithms and systems that may revolutionize the way traffic lights are regulated.

A smartphone based DSS platform for assessing transit service attributes

This paper presents a methodology for determining public transportation quality attributes, based on a decision support system (DSS). The platform, once set up, combines the capability of geographic information systems (GIS) to analyze spatial attributes and the smartphone mobile technology, which is a “smart” solution to collect dynamically bus locations and their cinematic variables. The DSS has been applied to a real case study in order to test its reliability. The results highlight a good flexibility of the platform combined with a good level of scalability and interoperability of the system that can be applied in any context. Moreover, the high penetration rate of smartphones among users and the system capability of disaggregating data in both space and time, makes the DSS useful to identify operational problems and take appropriate actions with a non-intrusive approach.

Analysis of Non-Conventional Roundabouts Performances through Microscopic Traffic Simulation

This research is focused on the applicability, in particular contexts, of roundabouts characterized by a non conventional geometry configuration. The methodology is based on the microsimulation approach, validated through a series of surveys on real case studies and traffic conditions. A microsimulation model (VISSIM, PTV), was applied in order to reproduce roundabouts geometry and to define vehicle flow parameters. The research results allow to evaluate roundabouts level of service as a function of geometric features and to establish the limits connected to the employment of noncircular roundabouts in different traffic scenarios.

Assessing public transport reliability of services connecting the major airport of a low density region by using AVL and GIS technologies

This paper presents a study of bus services operational performance through the analysis at a stop level of Automatic Vehicle Location (AVL) data, using the capability of Geographic Information Systems (GIS) to analyze spatial and temporal patterns of change. In particular, the analysis is focused on the study of the reliability of public transport services that connect the most important urban centers and the airport of a low density region. The intention is to suggest transport demand management policies aimed at shifting the modal split towards public transport modes as sustainable forms of mobility, encouraging intermodality. In order to determine average travel times and the standard deviation of travel times a specific statistical analysis has been carried out. The results of this analysis have been imported into a GIS package for a further investigation of the services reliability to highlight some critical aspects and adopt specific policies and opportune solutions.

Level of Safety on Two-Lane Undivided Rural Highways

Due to the great increase of congestion levels on transportation infrastructures researchers and practitioners have focused on the study of safety performance on road network to identify unsafe locations and assess the effectiveness of different countermeasures introduced at a given site to reduce unacceptable accident risk. Safety performance measures represent an useful tool for evaluating road safety conditions on the basis of objective parameters deducible from the vehicle kinematics. The focus of the present paper is on the assessment of the safety level on two-lane rural highway with a particular attention on rear-end interactions among different pairs of vehicles belonging to the traffic stream. The roadway safety performance study is based on the traffic conflict technique applied to vehicle maneuvers obtained experimentally from a frame by frame analysis of video-taped traffic data. The authors also explored qualitatively the possible relationship between safety level and traffic level of service. This aspect is very important because this kind of roads represents a large part of non-urban highways in many countries.

Localization issues in the use of ITS

The problem to rectify and optimize distance measures from satellites in GNSS devices has been thoroughly explored in many researches. Instead there is not much information on available procedures to replicate the observed errors. The replication of GNSS errors can, in fact, be useful in many traffic simulation scenarios to test for ITS performances. The purpose of this article is to present cases where such a methodology can be useful and then introduce a methodology for the explicit simulation of errors in GNSS systems. The proposed methodology is based on the experimental analysis of some statistical distributions. Such distributions, arising from multiple observations in the field, are able to reproduce the behavior of the error in time as a function of the factors that influence it. The analyzed data were extracted by the GPS/GLONASS sensors of common smartphones and compared with a high-precision GPS equipment. These data were evaluated in different signal coverage conditions, in an open field where the signal quality is expected to be better, suburban and urban areas, where the signal is expected to be worse. The analysis considers many aspects such as the signal reflection problems and the sudden loss of the signal because of a change of the received satellite constellation. The research was conducted by following various steps: a field survey through smartphones and high-precision instrumentation in different conditions, the creation of reference distributions for each parameter that can have an influence on the error, the analysis of correlation functions between the variables, and a final implementation of the proposed algorithm coupled with microsimulation. The paper intends to shed some light on this problem allowing scientist and developers of new ITS system methodologies to reproduce in a simulated environment not only the movement of single vehicles (as usually carried on with microsimulation) but also the data that could be obtained from on-vechicle GNSS instrumentation. The reproduction of this GNSS tracks can be useful to assess the overall response of some new ITS systems before implementing them in the field. The proposed simulation methodology could become a standard tool to help in making better decisions in ITS implementation and to develop better ITS systems.