Conversion of existing roundabouts into turbo-roundabouts: case studies from real world, Journal of Civil Engineering and Architecture 6(8)

Compared with roundabouts the main advantages of turbo-roundabouts are the reduction in the number of potential conflicting points and the lower speed of vehicles through the intersection; they both can improve road safety conditions at the junction. Moreover, the physical delimitation among lanes limits the side-by-side accident risk. These aspects make turbo-roundabouts more appropriate than roundabouts when a higher level of safety has to be guaranteed, particularly in presence of relevant pedestrian and two-wheels traffic volumes. The present paper has three main objectives : 1) to discuss general design criteria and functional principles of turbo roundabouts; 2) to give the geometric d…

EVALUATING CAPACITY AND EFFICIENCY OF TURBO-ROUNDABOUTS.

Recent evolution of roundabout design has been directed towards the so-called turbo-roundabout, with the aim of ensuring better safety conditions than those afforded by traditional schemes. The few turbo-roundabout installations so far implemented have not allowed sufficient research in order to analyze operational conditions and capacity models validated by field observations. In any case the theoretical approach to the functional study of turbo-roundabouts undoubtedly involves more complex aspects compared to typical roundabouts because of the paths of entering streams (constrained to get onto physically separated lanes), the “turbine” configuration of the circulatory carriageway, as well…

Understanding Safety-Related Issues for Pedestrians at Modern Roundabouts. Journal of Sustainable Development, 5(4):23-37

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 built is related to safety benefits, roundabout design features and implications in road casualties have been commented first to evaluate the influence of roundabouts on pedestrian safety and then to identify design elements that have such a high potential for traffic safety. At last, measures and treatments that can be taken in the roundabouts desi…

Improving reliability of road estimates based on high correlated accidents counts

Approccio teorico-sperimentale per l'analisi delle condizioni opertaive di rotatorie urbane non convenizonali.

I metodi tradizionali di analisi delle intersezioni a rotatoria non consentono una valutazione attendibile delle condizioni operative del traffico in presenza di schemi organizzativi dell’intersezione, nei quali la geometria, unitamente alla molteplicità delle situazioni di traffico ed all’inserimento in contesti vincolati, induce comportamenti di guida anche molto distanti da quelli osservabili in rotatorie convenzionali. Quanto evidenziato interessa, in particolare, gli schemi circolari di intersezione in area urbana, dove risultano particolarmente diffusi e si caratterizzano per requisiti geometrico-funzionali spesso distanti da quelli propri delle rotatorie convenzionali. I vincoli loca…

DERIVAZIONE DEI MODELLI PREVISIONALI PER LE ROTATORIE URBANE.

L'applicazione dell'analisi di sicurezza preventiva ad un itinerario urbano di una strada di quartiere

Recent Evolutions of Roundabouts: Methodological Issues and Practical Concerns.

The aim of the research is to provide a choice criterion between innovative roundabouts (turbo-roundabouts and flower-roundabouts) and double-lane roundabouts by evaluating convenience in terms of performances, when traffic demand is known. For this purpose, comparisons of operational performances at innovative roundabouts with regard to those at traditional roundabouts were developed. We started from consistent assumptions regarding the arrival process of major streams and used capacity models founded on gap-acceptance theory. Having in mind a bunched exponential headways distribution, we proposed adaptations of the Hagring model for estimating entry capacity at intersections under examina…

A generalized model for analyzing operational conditions at intersections in urban areas

Modeling traffic operations and drivers' behavioral parameters at not-conventional roundabouts. A theoretic-experimental approach

The inapplicability of current methods based on gap-acceptance theory for analyzing operational conditions at not-conventional roundabouts (very frequent in urban areas) seriously hampers the performance assessment; in practical applications, this also makes the choice of corrective design measures very uncertain. Starting from this considerations, the present paper shows the conceptual path followed for analyzing traffic operations at multilane-large-diameter not-conventional roundabouts. The research follows a theoretic-experimental approach that intends to put in a fair equilibrium the need both to match field observations and to have a general criterion to determine behavioral parameter…

Modello di capacità e valutazione delle prestazioni per le rotatorie a turbina.

L’evoluzione più recente delle intersezioni a rotatoria si è indirizzata verso schemi cosiddetti a turbina (turborotatorie) con l’obiettivo di garantire condizioni di sicurezza più elevate rispetto agli schemi tradizionali. I pochi esempi di realizzazione delle rotatorie a turbina non hanno tuttavia finora consentito di sviluppare metodi di analisi delle condizioni operative e modelli di capacità che possano vantare una validazione attraverso osservazioni di campo. In ogni caso, l’approccio teorico allo studio funzionale delle turborotatorie presenta aspetti decisamente più complessi di quelli delle rotatorie convenzionali sia a causa delle traiettorie dei flussi in ingresso (costretti ad i…

TURBO-ROUNDABOUT GENERAL DESIGN CRITERIA AND FUNCTIONAL PRINCIPLES: CASE STUDIES FROM REAL WORLD

Compared with usual roundabouts the main advantages of turbo-roundabouts are the reduction in the number of potential conflicting points and the lower speed of passing vehicles through the intersection; they both can improve road safety conditions at the junction. Also, the physical delimitation among lanes limits the side-by-side accident risk. These aspects make turbo-roundabouts more appropriate than roundabouts when a higher level of safety has to be guaranteed, particularly in presence of relevant pedestrian and two-wheels traffic volumes. In a previous paper authors proposed a theoretical approach to evaluate turbo-roundabouts capacity founded on gap acceptance theory. In particular, …

Genetic algorithm-based calibration of microscopic traffic simulation model for single-lane roundabouts

A calibration procedure for microscopic simulation models based on a genetic algorithm is proposed. Focus is made on single-lane roundabouts for which many random factors such as gap- acceptance affect operations. A comparison is performed between the capacity functions based on a meta- analytic estimation of critical and follow up headways and simulation outputs of a roundabout built in Aimsun microscopic simulator. Aimsun parameters were optimized using the genetic algorithm tool in MATLAB® which automatically interacted with Aimsun through a Python interface. Results showed that applying the genetic algorithm in the calibration process of the microscopic simulation model, a good match to…

Efficacia delle procedure di valutazione preventiva della sicurezza stradale.

Approccio teorico-sperimentale per l'analisi delle condizioni operative di rotatorie urbane non convenzionali

I metodi tradizionali di analisi delle rotatorie cadono in difetto in presenza di schemi organizzativi dell’intersezione, nei quali l’organizzazione geometrica, unitamente alla molteplicità delle situazioni di traffico ed all’inserimento in contesti vincolati, induce comportamenti di guida anche molto distanti da quelli osservabili in rotatorie convenzionali. Quanto evidenziato interessa, in particolare, l’ambito urbano, dove le intersezioni a circolazione rotatoria risultano particolarmente diffuse e si caratterizzano per requisiti geometrico-funzionali spesso distanti da quelli propri delle rotatorie convenzionali. Uno dei maggiori ostacoli che si incontrano nell’analisi delle condizioni …

Improving reliability of road safety estimates based on high correlated accidents counts

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 correlation; the usual application of GEEs to safety analysis uses robust (or sandwich) estimates of regression coefficients under the independence hypothesis for the working correlation matrix. This practice is justified by the robustness of the GEE procedure against misspecification of the response correlation structure. Nevertheless, with this method,…

Modeling capacity at multilane-large-diameter roundabouts. An exploratory analysis.

Calibration of Speed-Density Relationships for Freeways in Aimsun

The first application of a calibration methodology which uses speed-density relationships in the microsimulation calibration process is described in this article. Traffic patterns were implemented developing speed-density relationships for empirical and simulated data. For empirical relationships reference was made to traffic data observed at A22 Freeway (Italy). Aimsun microscopic traffic simulator software was then used to obtain analogous relationships for a test freeway segment under uncongested traffic conditions. Thus on field conditions were reproduced varying some calibration parameters until a good matching between field and simulation was achieved. The closeness between empirical …

A microsimulation calibration methodology based on speed-density relationships for freeways

This paper describes the calibration methodology based on speed-density relationships in the microsimulation calibration process, stated that they represent the traffic flow phenomenon in a wide range of operational conditions and well summarize all the information that may be collected on field (or following a run of the microsimulation model) on two of the three key variables of traffic flow. The matching of speed-density relationships from field and simulation was evaluated using statistical analysis as technique of pattern recognition. A test freeway segment under uncongested traffic conditions was selected as case study; based on traffic data observed at A22 Brenner Freeway, Italy, sta…

I PRINCIPI DELL'ORGANIZZAZIONE GEOMETRICA E FUNZIONALE DELLE INTERSEZIONI A RASO LINEARI

Ruolo dell'infrastruttura nella sicurezza stradale

La via Libertà a Palermo

Effect of the construction process on the performances of asphalt paving mixes with crumb rubber from scrap tires

This paper presents the results of an experimental study on the use of CRM (Crumb Rubber Modifier) in bituminous mixtures for asphalt pavements, using a Dry Process. Employing experimental methods capable of ensuring that the mixtures obtained and the stress conditions that they undergo in pavements are representative, we clarify some aspects relating to the design and production of mixtures; we also show the effects of the bitumen-rubber interaction on mechanical performances (fatigue resistance and rutting). Among the various factors involved in manufacture, a particular investigation was carried out on the effects of asphalt content, mixing temperatures and mixture compaction. The experi…

EMISSION FACTORS, VEHICLE MODAL ACTIVITY AND ROAD OPERATIONS. A MESOSCOPIC APPROACH

Current studies underline that vehicle emissions are highly linked to modal vehicle activity and a modal approach to traffic-related air quality modeling is suitable to estimate mobile source contribution to air quality. Pollutant emissions depend on characteristics of vehicles in traffic flow and on road operating conditions predictable after the implementation of the road project; then, the usual emission rate models do not predict properly the on-road vehicles emissions of modal traffic events, such as those ones occurring at intersections. Moreover modal activity analysis carried out at micro scale level, as required by modal emission models, will be still necessary to value reliable em…

ROAD SAFETY IN URBAN AREAS: A PLACE OF MYTHS