Safety Evaluation of Turbo-Roundabouts with and without Internal Traffic Separations Considering Autonomous Vehicles Operation

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 Surrogate Safety Assessment Model (SSAM), the research aims to evaluate the safety benefits of turbo-roundabouts where the lanes are physically separated by raised curbs, compared to roundabouts without such curbs. The paper will then describe the methodological path followed to build VISSIM models of turbo-roundabouts with and without raised curbs in order to calibrate the simulation models and estimate the potential conflicts when a higher percentage of CAVs are introduced into the traffic mix. A criterion has been also proposed for setting properly the principal SSAM filters. The results confirmed both higher safety levels for turbo-roundabouts equipped with raised lane dividers compared to turbo-roundabout solutions without curbs, and better safety conditions under the traffic mix of CVs and CAVs. Therefore, it follows that, in absence of crash data including CAVs, the surrogate measures of safety are the only approach in which the safety performance of any roundabout or road entity can be evaluated

A Novel Architecture of Parking Management for Smart Cities

AbstractParking is becoming an expensive resource in almost any major city in the world. Current technically advanced solutions for parking management are concerned with the application of secured wireless network and sensor communication for parking reservation. Moreover new rules concerning financial transactions in mobile payment allow the definition of new intelligent frameworks that enable a convenient management of public parking in urban area. The paper discusses the conceptual architecture of IPA (Intelligent Parking Assistant) which aims at overcoming current parking management solutions and thereby becoming a leading paradigm for the so called “smart cities”

Estimation of Passenger Car Equivalents for Two-Lane and Turbo Roundabouts Using AIMSUN

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 methodological approach which used traffic microsimulation to estimate PCEs. Focus is made on a case study which considered the conversion of a two-lane roundabout into a basic turbo roundabout with comparable size. Empirical capacity functions for both roundabouts were derived as target values to which simulated capacities by lane were compared. In order to estimate the PCEs a criterion of equivalence based on the amount of capacity used by cars and heavy vehicles is presented. AIMSUN allowed to simulate traffic conditions with different percentages of heavy vehicles at both roundabouts. Thus, variation of traffic conditions where mixed fleets operate was explored. A comparison was made between the PCEs estimated for each entry lane characterized by similar mechanism of entry maneuver. The results indicated there is a need to distinguish the impact of heavy vehicles when operational performance of a two-lane roundabout or a turbo-roundabout should be examined. Especially when circulating flows increase, a higher PCE value is expected than the value that the Highway Capacity Manual proposes for roundabouts

accounting for dispersion and correlation in estimating safety performance functions an overview starting from a case study

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 for dispersion and correlation, the paper presents the methodological path followed in estimating a SPF for urban four-leg, signalized intersections. Since the case study exhibited signs of underdispersion, a Conway-Maxwell-Poisson Generalized Linear Model (GLM) was fitted to the data; then a quasi-Poisson model in the framework of Generalized Estimating Equations (GEEs) was performed in order to account for correlation. Results confirm that dispersion and correlation are phenomena that cannot be eluded in the estimation of SPFs under penalty of loss of efficiency in estimating model parameters. Generalized Estimating Equations overcome this problem allowing to incorporate together dispersion and temporal correlation when a quasi-Poisson distribution is used for modeling crash data. Moreover, whereas GEE regression is handy (many statistical software packages have already implemented GEE functions), the interest of COM-Poisson regression, because of difficulties in interpreting the model parameters and in arranging COM-Poisson codes, is still limited to the research field

exploring effects of area wide traffic calming measures on urban road sustainable safety

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 can be a realistic objective. Several studies highlight that traffic calming treatments can significantly reduce road accidents in urban areas. Nevertheless, the increase of the accident rate per kilometre travelled has been found in urban areas as result of the so-called accident migration phenomenon. Starting from these considerations, the paper discusses the effects of traffic calming measures on road safety. The paper also aims to provide a concise overview of knowledge on the potential of the meta-analysis method in detecting the true effect of traffic calming measures on road safety. Therefore, the role of the road network planning and the characteristics of urban road network that have to be consistent to the traffic calming objectives are examined. Finally, authors suggest a methodological procedure for implementing a traffic calming zone in residential areas, from planning level to road design

ESTIMATING TRAFFIC OPERATIONS AT MULTI-LANE ROUNDABOUTS: A CASE STUDY

ABSTRACT 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 operational performances have the shortcoming of not representing the interdependencies between entering and circulating vehicles at multi-lane roundabouts. An analytical capacity model derived from field observations was developed for this kind of intersections in a previous study. The complexity of the model lies in the difficulty of observing the behavioral parameters which are needed to implement the model. A procedure to get unknown behavioral parameters from traffic surveys is here proposed. This concerns saturation headways, often eluding direct observations due to rare occurrences of traffic conditions in which they can be observed. The unknown parameters were estimated through a regression model using onfield data collected at a multi-lane roundabout. The presence of data correlation within a cluster of observations required the estimation of the regression parameters through a generalized estimating equation model. Results gave insight into the analysis of operations at multi-lane roundabouts, containing evidence to support assumptions made for the estimation of unobservable parameters

Environmental Performance Evaluation at Urban Roundabouts

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 Vehicle Specific Power methodology which needs second-by-second speed profiles both gathered in the field and simulated in AIMSUN. The versatility of the micro-simulation model for a calibration aimed at improving accuracy of the emissions estimates was tested in order to ensure that second-by-second trajectories experienced in the field properly reflected the simulated speed-time profiles. The results confirmed the feasibility of the smart approach that integrates the use of fieldobserved and simulated data to estimate emissions at urban roundabouts. It is also revealed friendly in collecting information via smartphone and in the subsequent data analysis, and provided new opportunities for a large-scale data collection through a digital communit

Environmental Performance Assessment of Urban Roundabouts

To meet continuous and sustainable improvement on road infrastrucutures, 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 trajectory data collected in the field, the Vehicle Specific Power methodology and a microscopic traffic simulation model for estimating emissions at urban roundabouts. For a first characterization of the emissive phenomenon reference was made to an existing two-lane roundabout in Palermo, Italy, where vehicle trajectory data were collected using a smartphone app in a test vehicle. The case study addresses the issue of converting existing roundabouts into turbo roundabouts, and gives an insight into how to assess the impacts of alternative designs from an environmental perspectiv

Safety evaluation of turbo roundabout with and without internal traffic separations considering autonomous vehicles operation

The paper presents a microsimulation approach for assessing the safety performance of turbo-roundabouts where Cooperative Autonomous Vehicles “CAVs” have been mixed with conventional vehicles “CVs”. Based on the analysis of vehicle trajectories from VISSIM and subsequent analysis of traffic conflicts through the Surrogate Safety Assessment Model (SSAM), the research aims to evaluate the safety benefits of turbo-roundabouts where the lanes are physically separated by raised curbs compared to roundabouts without curbs. The paper shall also lead to describe the methodological path followed to build VISSIM models of turboroundabout with and without raised curbs, to calibrate the simulation models, and to estimate the potential conflicts when the percentages of CAVs are introduced into the traffic mix. A criterion has been also proposed for setting properly the principal SSAM filters. The results confirmed both higher safety levels for turbo roundabouts equipped with raised lane dividers compared to turbo roundabout solutions without curbs, and better safety conditions under traffic mix with CAVs. Therefore, it follows that in absence of crash data including CAVs, the surrogate measures of safety are the only approach to evaluate the safety performance of a roundabout and any road entit

A New Experimental Investigation for Improving Bridge Management Systems and Road Operation Sustainability

Generally, during maintenance operations on bridges and motorway viaducts, the circulation of vehicles is limited or suspended. This causes significant economic losses due to the increase in the costs of transport: delays, increased fuel consumption, higher emissions of pollutants into the atmosphere, increased risk of accidents, etc. However, few studies have analyzed the influence of bridge vibrations on the final mechanical properties of the cement mortar placing during ordinary bridge service. As such, interest is increasing in repair techniques that could achieve high structural performance without reducing road service levels. This paper provides the results obtained through an innovative laboratory trials campaign that evaluated the influence of vibrations on the mechanical properties of high-performance mortar used for repairing bridge decks. The results of 24 cubic and prismatic specimens showed the relationship between the traffic-induced vibrations and the mechanical characteristics of the studied mortar. The findings can be considered as the first methodologic step that is necessary to address further field studies, drawing a detailed link between the repair techniques and transportation user costs. Based on the obtained results, a synthetic bridge management system framework was developed that merges the road function into the structural issue with the goals of increasing the resilience of road networks and optimizing the maintenance resources budget