Anna Grana

University of Palermo | UNIPA · Department of Engineering

Nowadays, the majority of society decides to use individual transport for everyday travel, which negatively affects the congestion of cities. Nevertheless, in the transport policy of the European Union, public transport is becoming more and more important, which is reflected in strategic documents in the field of sustainable transport development....

Road safety is a crucial global concern because of the high number of fatalities and injuries resulting from road crashes each year. Median crossover collisions are among the most dangerous crashes that happen on highways, frequently leading to serious or fatal injuries. The main approach to decreasing the occurrence of these types of crashes is th...

The attractiveness of an offer is the main factor in determining the demand for public transport services, which goes beyond just the transportation itself and includes various accompanying aspects. Before starting their journey, many people confront the dilemma of choosing a mode of transportation. Often, this choice depends on individual habits....

This paper presents a simulation-driven method for assessing the safety and efficiency of traffic at roundabouts incorporating connected and automated vehicle (CAV) technology. Utilizing the newly proposed CAV-based factors specified by the Highway Capacity Manual (HCM) provided a practical framework for analyzing capacity dynamics across various t...

This paper explores the domain of intelligent transportation systems, specifically focusing on roundabouts as potential solutions in the context of smart mobility. Roundabouts offer a safer and more efficient driving environment compared to other intersections, thanks to their curvilinear trajectories promoting speed control and lower vehicular spe...

The introduction of connected automated vehicles (CAVs) on freeways raises significant challenges, particularly in interactions with human-driven vehicles, impacting traffic flow and safety. This study employs traffic microsimulation and surrogate safety assessment measures software to delve into CAV–human driver interactions, estimating potential...

Urban mobility underscores the vital importance of ensuring traffic efficiency on road segments, intersections, and transportation networks, especially in challenging circumstances. In this perspective, the essential approach to improving urban intersection efficiency should involve understanding critical factors for maintaining operational perform...

Which intersection geometry or type of control mode may affect the efficiency and resilience at urban isolated intersections before and after a disruption as a storm? Is the research question that is expected to answer in this paper. Starting from some types of urban road intersections from the real world, this paper presents the first conceptualiz...

Traffic-calming measures (TCMs) are non-invasive devices designed to improve road mobility and urban areas on a human scale. Despite their potential, they have been in use for a long time and now have to deal with the latest technological innovations in the automotive field, such as cooperative driving technologies (CDTs), to improve energy efficie...

There is increasing interest in connected and automated vehicles (CAVs), since their implementation will transform the nature of transportation and promote social and economic change. Transition toward cooperative driving still requires the understanding of some key questions to assess the performances of CAVs and human-driven vehicles on roundabou...

Walking is a basic form of activity for every human being and has many advantages, including health, economic and environmental benefits. Every journey made using various means of transport begins and ends on foot. As is well known, the group of road users particularly exposed to the risk of serious injury in road accidents, apart from cyclists, al...

E-scooters as a new form of mobility are gaining more and more popularity. This popularity results from the flexibility of this mode of transport, but above all from the positive impact on the natural environment through the much higher energy efficiency of an e-scooter compared to a motor vehicle (according to the literature the rate is 2 km per k...

Connectivity and automation are technologies applied in combination to achieve increases in road safety, traffic efficiency and energy savings. Despite their potential, there are still many open questions regarding how roadway capacitycapacity will be affected and what methods should be employed to assess the expected benefits in the transportation...

Despite the potential of connected and automated vehicles (CAVs), there are still many open questions on how road capacity can be influenced and what methods can be used to assess its expected benefits in the progressive transition towards fully cooperative driving. This paper contributes to a better understanding of the benefits of CAV technologie...

Transportation, like other spheres of human activity, is constantly changing due to economic development [...]

In line with globally shared environmental sustainability goals, the shift towards citizen-friendly mobility is changing the way people move through cities and road user behaviour. Building a sustainable road transport requires design knowledge to develop increasingly green road infrastructures and monitoring the environmental impacts from mobile c...

Transformation toward greener, healthier and safer management of urban mobility demand is needed soon. Smart tools are available to assess the impact of new infrastructural projects and road facilities also from an environmental point of view. In this pilot study pollutant emissions at a sample of urban roundabouts were estimated employing the Vehi...

To meet continuous and sustainable improvement on road infrastructures, new technologies and smart devices are encouraging the development of a mobile crowdsensing system for collecting and monitoring data to be used in efficiency assessment. In this view, the paper proposes a methodological approach that employs in an integrated way vehicle trajec...

Transportation and technological development have for centuries strongly influenced the shaping of urbanized areas. On one hand, it undoubtedly brings many benefits to their residents. However, also has a negative impact on urban areas and their surroundings. Many transportation and technological solutions lead, for example, to increased levels of...

The paper presents a microsimulation approach for assessing the safety performance of turbo-roundabouts where Cooperative Autonomous Vehicles “CAVs” have been introduced into the traffic mix alongside conventional vehicles “CVs”. Based on the analysis of vehicle trajectories from VISSIM and subsequent analysis of traffic conflicts through the Surro...

The importance of being circular reflects one of the key concepts of the life-cycle thinking that promotes the sustainable production of goods and services. If it is true that the analysis of the product life-cycle is fundamental to optimize the use of resources and to plan for the future reduction of adverse effects on urban environment, it is als...

Increasing concern about global warming and air quality has meant an increasing use of energetic and environmental indicators in roundabout design. This research compares different suburban roundabouts in terms of traffic performance, pollutant and noise emissions through an integrated empirical assessment. Field measurements were carried out with...

The paper addresses issues related to Passenger Car Equivalents (PCEs) at roundabouts. Compared to other road units, the curvilinear elements of roundabout geometric design may impose greater constraints on vehicular trajectories and have a significant effect on the swept envelope of heavy vehicles. Specifically, the aim of the paper is to present...

The paper describes the pilot study conducted to assess the feasibility of the empirical approach utilizing vehicle trajectory data from a smartphone app and the Vehicle-Specific Power methodology to estimate pollutant emissions at urban roundabouts. The goal of this research phase is to acquire instantaneous speed data from a sample of six roundab...

Passenger Car Equivalents (PCEs in the following) are used to transform a mixed fleet of vehicles into a fleet of equivalent passenger cars and to analyze capacity and level-of-service of roads and intersections. Most roundabouts guidelines propose constant values for PCEs but a single PCE value can result improper under heterogeneous traffic condi...

This paper addresses issues on road safety analysis through microscopic traffic simulation models. The Surrogate Safety Assessment Model (SSAM) was applied to read vehicle trajectory files generated by two micro-simulators and then calculate surrogate measures of safety. Since safety assessment of any road entity can provide different results based...

The paper presents a microsimulation-based approach for roundabout safety performance evaluation. Based on a sample of Slovenian roundabouts, the vehicle trajectories exported from AIMSUN and VISSIM were used to estimate traffic conflicts using the Surrogate Safety Assessment Model (SSAM). AIMSUN and VISSIM were calibrated for single-lane, double-l...

The paper introduces a methodological approach based on genetic algorithms to calibrate microscopic traffic simulation models. The specific objective is to test an automated procedure utilizing genetic algorithms for assigning the most appropriate values to driver and vehicle parameters in AIMSUN. The genetic algorithm tool in MATLAB ® and AIMSUN m...

Calculation of passenger car equivalents for heavy vehicles represents the starting point for the operational analysis of road facilities and other traffic management applications. This paper introduces a criterion to find the passenger car equivalents that reflect traffic conditions at double-lane roundabouts, where the capacity is typically estim...

PurposeIn gap-acceptance theory the critical and the follow-up headways have a significant role in determining roundabout entry capacities which in turn depend on circulating flow rates under a specified arrival headway distribution. Calculation considers single mean values of the gap-acceptance parameters, neglecting the inherent variations in the...

Passenger car equivalents for heavy vehicles are required to carry out capacity calculations and perform operational analysis of any road entity (roadway segments or intersections). At single-lane roundabouts, the constraints to the vehicular trajectories imposed by the curvilinear geometric design and the driver's gap acceptance behaviour are expe...

This chapter describes the genetic algorithm-based calibration procedure for a microscopic traffic simulation model, focusing on freeways and modern roundabouts. For both case studies, the genetic algorithm tool in MATLAB® was applied in order to reach the convergence between the outputs from Aimsun microscopic simulator and the observed data. The...

Turbo-roundabouts represent an innovative scheme of modern roundabouts which provides a spiraling traffic flow and requires drivers to choose their direction before entering the intersection, since raised lane separators mark the lanes on the ring. The configuration of the turbo-roundabout makes that patterns of conflict at entries with one and two...

Several studies and researches have shown that modern roundabouts are safe and effective as engineering countermeasures for traffic calming, and they are now widely used worldwide. The increasing use of roundabouts and, more recently, turbo and flower roundabouts, has induced a great variety of experiences in the field of intersection design, traff...

Due to its geometric design, turbo-roundabouts impose greatest constraints to the vehicular trajectories; by consequence, one can expect a more unfavourable impact of heavy vehicles on the traffic conditions than on other types of roundabouts. The present paper addresses the question of how to estimate Passenger Car Equivalents (PCEs) for heavy veh...

Purpose The critical and follow-up headways are the two gap-acceptance parameters which explain the traffic interaction of a minor street vehicle when enters the roundabout, merging into or crossing one or more circulating (major) streams. Several studies and researches provide measurements of critical and follow-up headways from real data at round...

In this paper a method of estimation of the passenger car equivalents for heavy vehicles on freeway is described. The variation in traffic quality was evaluated basing on a traffic demand characterized by different percentages of heavy vehicles. Aimsun micro-simulator was used to isolate traffic conditions difficult to capture on field, to replicat...

This paper presents the first results of a research which applied a genetic algorithm to calibrate a microscopic traffic simulation model based on speed-density relationships. A large set of traffic data collected from the A22 Freeway, Italy, was used and a comparison was performed between the field measurements and the simulation outputs obtained...

In the last few years a considerable amount of safety models and evaluation tasks have been developed and specifically dedicated to roundabouts. Several safety performance functions (SPFs), indeed, have been implemented for roundabouts worldwide. Since SPFs are developed using crashes, traffic volume and other characteristics of a specific site (or...

In the paper, a choice criterion between flower roundabouts and double-lane roundabouts is proposed, focusing on operational benefits that can derive from one scheme over the other, and outlining a general framework for benefit-cost analysis. In order to assess operational benefits of innovative roundabouts over modern roundabouts, a comparative an...

Starting from consideration that urban intersections are sites with promise for safety and operational improvements, the paper describes the steps taken to develop a crash predictive model for estimating the safety performance of urban unsignalized intersections located in Palermo, Italy. The focus is on unsignalized four-legged one-way intersectio...

This paper addresses traffic modeling issues at urban multi-lane roundabouts where, despite circulating vehicles have priority, negotiation of the right-of-way can occur between antagonist traffic flows, as a result of minor drivers' failing to obey the nominal operating rule (stop or yield control). Existing models for the estimation of operationa...

In this paper the calibration of a traffic microsimulation model based on speed-density relationships is presented. Hypothesis test was applied in the calibration process to measure the closeness between empirical data and simulation outputs and determine whether the difference between (observed and simulated) speeddensity relationships was statist...

In this paper, a criterion for predicting the reliability of freeway traffic flow is presented. The idea is based on an analysis of spot speed time series divided into sequences of events of random and homogeneous traffic processes. For each process, the flow rate and density were calculated; then the relationships between parameters of spot speed...

According to the state-of-the-art of the methodologies, the development of safety performance functions (SPFs) for road sections and intersections requires the employment of statistical models to predict expected crash frequencies on the basis of traffic volumes and site characteristics to be surveyed and used as input to models. Nevertheless, lite...

In statistical analysis of crash count data, as well as in estimating Safety Performance Functions (SPFs), the failure of Poisson equidispersion hypothesis and the temporal correlation in annual crash counts must be considered to improve the reliability of estimation of the parameters. After a short discussion on the statistical tools accounting fo...

In this paper the performance level of basic turbo-roundabouts and double-lane roundabouts are compared. Cowan's M3 headway distribution was chosen to take into account bunched vehicles moving along each circulating lane; the Hagring model was adopted to evaluate entry capacity both at turbo-roundabout and at double-lane roundabout.The comparative...

Starting from assumptions regarding the arrival process of circulating streams and according to models based on the gap-acceptance theory, the paper is aimed at comparing operational performances between basic turbo-roundabouts and double-lane roundabouts. The paper proposes applications of the Hagring model for entry capacity estimations at double...

The South Korean Government established a high-speed rail line in May 1989 and gave a new boost to the railway sector with regard to infrastructure and rolling stock. The South Korean Train eXpress, well known by the acronym of KTX, is the high-speed train manufactured in South Korea and represents the high-speed railway system of the Country. The...

This article summarizes a research program designed to assess operating conditions through capacity estimation at not-conventional roundabouts characterized by a central island with a large diameter and by two (or more) entering and circulating lanes. Although giving priority to vehicles on circulatory roadway is the nominal operating rule, on-fiel...

This paper examines the safety-related issues for pedestrians at modern roundabouts. For this purpose findings of research studies documented in the scientific literature and best practices have been examined trying to focus on roundabout installations by a pedestrians safety perspective. Whereas one of the main reasons for which roundabouts are bu...

Polluting emissions depend on vehicle characteristics and on traffic conditions expected after the construction of a road project. Nevertheless, in the assessment of new projects, the task of road designer becomes uncertain when the reduction in polluting emissions has to be evaluated. Moreover, vehicle emissions are highly linked to modal vehicle...

For some years now, problems relating to gas emissions that affect climate and result from human activities have assumed a global dimension of large importance. The climate is, indeed, influenced by the concentrations of some pollutants in the atmosphere; these pollutants trap the long wave radiation emitted by the Earth and alter the energy balanc...

Poisson basic assumption of equidispersion is often too much restrictive for crash count data; in fact this type of data has been found to often exhibit overdispersion. Underdispersion has been less commonly observed, and this is the reason why it has been less convenient to model directly than overdispersion. Overdispersion and underdispersion are...

Pedestrians are important users of the transportation system, but most guidelines have given them little importance in the geometric design of roads and intersections. In these cases it can be difficult for vehicles and pedestrians to share the road safely, particularly at intersections where vehicle-pedestrian conflicts (and the risk of vehicle–pe...

Traffic calming schemes refer to a combination of road network planning and engineering measures to minimize undesirable effects of traffic in residential areas. The traffic calming role in urban road network management is, indeed, to enhance road safety as well as other aspects of liveability for the citizens; in this context accident reduction ca...

It is generally accepted that accident rates tend to be higher at intersections than on through sections of a road. This is particularly frequent in urban area where roads are characterized by intersections in close succession; moreover, the safe and effective operations of the urban road system can be significantly affected by safety conditions at...

The role of traffic calming schemes in urban network management is mainly to minimize the undesirable effect of traffic in residential areas; in this context accident reduction can be a realistic objective. Several studies, indeed, inform us that traffic calming is a major part of the treatments available to reduce road accidents in urban areas. Pa...

The inapplicability of current methods for analyzing the operations of notconventional urban roundabouts (i.e. not referable to standard schemes) seriously hampers the assessment of their operational performances. Moreover, local constraints and the road network structure have produced lots of geometric layouts that make it hard to propose a framew...

Traffic calming schemes refer to a combination of road network planning and engineering measures to minimize undesirable effects of traffic in residential areas. The traffic calming role in urban road network management is, indeed, to enhance road safety as well as other aspects of liveability for the citizens; in this context accident reduction ca...

The definition of decision support tools for identifying ex ante evaluation issues for road safety measures is a new challenge for policymakers and designers managing road networks with the intention of improving traffic safety for roads of their competence. This is consistent with explicit strategies on sustainability in the transport sector estab...

Calibrating a safety performance function (SPF) with many years of accident data creates a temporal correlation that traditional model calibration procedures cannot deal with. It is well known that generalized estimating equations (GEE) models are able to incorporate trends into accident data and thus overcome difficulties in accounting for correla...

This paper proposes a methodology of valuation for the urban environment, trying to answer questions and problems deriving from new road installations, or functional requalifications in existing road infrastructures, in accordance with specific practices already well-known as Urban Impact Assessment (UIA). More generally, the objective of the urban...

The available knowledge of traffic safety at roundabouts is not a complete reference for geometric design; where there are organizational schemes for junctions characterized by a geometric design, quite different driving behaviours are required from those that are observable at roundabouts. This is very frequent in urban areas, where the existing c...

The roundabout installations in urban areas are often conditioned by the existing constraints of different kind (particularly physical and topographical ones), compelling road engineers to make "compromise solutions" compared with the traditional geometric design standards of roundabouts; operational performances and risk conditions, in their turn,...