Antonio Pratelli

Design of Modern Roundabouts in Urban Traffic Systems

This paper provides an overview of modern roundabouts design and practice. Modern roundabout have become an issue of great interest over the last decade in Italy. This fact is partially drawn on the great success of roundabout traffic solutions in some European countries, where intersections design practice has changed in consequence of the performances gained with roundabouts and their general good acceptance by drivers. Modern roundabouts can have significant impacts and benefits in terms of circulation safety, delays and capacity.

Gap Acceptance Parameters for HCM 2010 Roundabout Capacity Model Applications in Italy

This paper deals with the field data observation and successive application of estimation procedures in order to estimate follow-up headway and critical headway at roundabouts. Average follow-up headway and average critical headway are two key parameters in the new roundabout capacity model presented in the 2010 edition of the Highway Capacity Manual (HCM). The HCM 2010 capacity model was developed as an exponential regression model with parameter estimates based on gap acceptance theory. Gap acceptance models are strongly affected by driver behaviour and local habits. Follow-up headways can be field measured, while critical headway cannot be obtained directly. The paper mainly aims to check if general suggested values are wellsuited also for Italy or not. There have been numerous techniques developed for estimating critical headway. In order to perform a better check of a sample of experimentally observed values, three different procedures are chosen and applied. The first is a quite popular mathematical method based on maximum likelihood technique. The second is a statistical method based on the median of the observed sample distribution. The third is a graphical method known as Raff’s method. All these three methods require information about the accepted gap and the largest rejected gap for each driver. Therefore a sample of field data was recorded by digital camera and processed following the instructions suggested by NCHRP. The sample data of critical headway and follow-up headway are gathered in seven selected roundabouts located in Northern Tuscany (Italy). Our first obtained results indicate that the average critical headway is significantly lower than the values recommended by some international references. However, the average follow-up headway is only higher than that

Estimation Of Gap Acceptance Parameters For HCM 2010 Roundabout Capacity Model Applications

This paper deals with the field data observation and successive application of estimation procedures in order to estimate follow-up headway and critical headway at roundabouts. Average follow-up and average critical headway are two critical parameters in the new roundabout capacity model presented in the 2010 edition of the Highway Capacity Manual (HCM). The HCM 2010 capacity model was developed as an exponential regression model with parameter estimates based on gap acceptance theory. Gap acceptance models are strongly affected by driver behaviour and local habits. Follow-up headways can be field measured, while critical headway cannot be obtained directly. The paper mainly aims to check if general suggested values are well-suited also for Italy or not. There have been numerous techniques developed for estimating critical headway. In order to perform a better check of a sample of experimentally observed values, three different procedures are chosen and applied. The first is a quite popular mathematical method based on maximum likelihood technique. The second is a statistical method based on the median of the observed sample distribution. The third is a graphical method known as Raff’s method. All these three methods require information about the accepted headway and the largest rejected headway for each driver. Therefore a sample of field data was recorded by digital camera and processed following the instructions suggested by NCHRP. The sample data of critical headway and follow-up headway are gathered in seven selected roundabouts located in Northern Tuscany (Italy). Our first obtained results indicate that the average critical headway is significantly lower than the values recommended by some international references. However, the average follow-up headway is only higher than that recommended for the State of

Visibility, Perception and Roundabout Safety

In Italy, over the past fifteen years, modern, or second generation roundabouts have become very popular. On these roundabouts, entering vehicles must yield to vehicles already within the circle. This modern design provides for much higher capacity of operation. Although first implemented in the UK in the 1960s, it took twenty years for the second generation to begin to spread to other European countries. Between 1987 and 2002, in particular, Germany, France and Switzerland conducted research that led to standards techniques that, along with English ones, now comprise the major technical references. The causes of the delay in implementation are uncertain and the subject of much speculation. The United States has only recently begun implementation, as it was not until the 1998 version did a chapter on roundabouts appear in the Highway Capacity Manual (developed further in the 2000 edition). In Italy, the first standards were proposed for the 1993 New Road Code, but it was not until 2004 that the standards were passed through national legislation. However, these codes are approximate and inadequate, and lack elementary technical foundations (see for instance Art. 4.5 of D.M. 19/04/2006, no.1699). A quick calculation for 4 legs and 60 meters diameter is sufficient to demonstrate its failure and infeasibility. The design of a roundabout, like that of any other road element, should be based on principles of safety, and should be deployed in a systemic context that combines geometric characteristics to meet capacity requirements – the perception of road space is also important. When designing a roundabout, the engineer should consider simultaneously both safety factors and capacity. But in addition to using geometric standards, formulas and models, aspects of perception and visual appeal should be considered.

A New Data-Driven Approach to Forecast Freight Transport Demand

Transport modeling, in general, and freight transport modeling, in particular, are becoming important tools for investigating the effects of investments and policies. Freight demand forecasting models are still in an experimentation and evolution stage. Nevertheless, some recent European projects, like Transtools or ETIS/ETIS Plus, have developed a unique modeling and data framework for freight forecast at large scale so to avoid data availability and modeling problems.

THE COMBINED ZONE AND FARE PLANNING PROBLEM

This paper looks at the problem of planning an integrated transit system from the viewpoint of optimal fares and zone design. More succinctly, the matter is how to plan an integrated fare system that allows each passenger to travel within different zones with a single zone-based ticket. A 2-level model is given, which is both quite near to real operation practices and makes the planner able to consider various transit firms operating within the same context. The main problem is divided into 2 distinct subproblems: one for the fare problem, and the other for the zone problem, solved sequentially. The fare problem leads to the minimization of an aggregated cost function that is mainly related both to the budget needs of each transit agency, and changing in fare levels for the patronage. The zone problem is solved by a heuristic method which was set up to randomly search for the optimal zone configuration reflecting a given fare policy. Computational test results of the proposed model applied on a real database gathered in the metropolitan area of Florence are also reported.

Car-sharing Relocation Strategies:A State Of The Art

Traditional car sharing systems are round-trip and require advance reservations. The advances of ICT and vehicle automation allow to improve car sharing systems and to provide users with greater flexibility. As it concerns reservation, new car sharing systems offer users open-ended reservation and/or instant access. As it concerns the trip typology, new car sharing systems are multiple station shared vehicle systems (MSSVS). Roundtrips still occur in this type of system, however there is a large number of one-way trips made between the multiple stations. Operating an MSSVS is much more difficult than operating a round-trip shared vehicle systems. The problem is that the system can quickly become imbalanced with respect to the number of vehicles at the multiple stations. These systems are called new (or second) generation car sharing systems. Third generation systems are the last being developed; in these systems vehicles can be accessed at any point of the area. An overview of all these car sharing systems is provided in this paper.

Calibration of a method for selecting roundabouts as a function of the inner island treatment

It is generally accepted that a driver’s ability to perceive, recognize, and react to surroundings contributes to safer roads. The objective of this paper is to investigate the perceptibility of roundabouts as influenced by their most distinctive feature – the central island treatment. Previous work has shown how visual perception of central island treatment can improve road safety performance. Recently, the authors have suggested a roundabout central island treatment classification scheme with three categories: Reduced, Compressed and Slender. Classifying roundabout central island treatment types was necessarily somewhat subjective. This paper introduces a more quantitative measure for central island visual perception, based on the theory of visual intrusion as measured by the solid angle subtending the central island treatment. Data were collected using laser instruments, Google Streetview ® and Google Earth ® , and the related solid angles have been estimated for a large sample of roundabouts located both in Tuscany (Italy) and in the United States. The classification scheme is analyzed using the nonparametric Fishers exact test which shows the central island treatment classification scheme is not associated with roundabout size. Therefore, central island treatment can be utilized as a unique metric for categorizing roundabouts. Descriptive statistics indicate that roundabouts with compressed island treatments have the largest solid angles (and implied visibility) when compared to either reduced or slender treatments, which have similar levels of visual intrusion as estimated by their solid angle.

Roundabout Perception: Review of Standards and Guidelines for Advanced Warning

This paper deals with roundabout visibility and perception design requirements, including available standards and guidelines in the US and Europe for warning signs. To provide for the highest levels of safety, visual perception of junctions is important even where advance warning signs are provided, to reinforce driver knowledge and confidence in their actions. For roundabouts, three different types of central island development are recently suggested to affect their visual perception, and the related classification defines the reduced, the compressed and the streamlined, or slender, central island development. The paper proposes new methodologies to test this perceptibility of various roundabout designs and developments. Two research strategies based on the specific roundabout visual intrusion defined by the solid angle are outlined: on-site stand-by/2D and virtual video/3D. Finally, some preliminary results are discussed in view of selecting original and proper standards. Moreover, future research is suggested for extending the methodology to more comprehensive application.

A Feasibility Study for New Transport Connections between Italy and Algeria

The present study is part of the Executive Scientific Project 2 in the ItalMed Project which aims to elaborate a feasibility study for new transport connections between Italy and Algeria. The main objectives of the study are to increase the degree of economic integration between the two countries and improve commercial exchanges and direct investments in Algeria by Italian private companies. Moreover, the study tries to promote Italy’s role as logistic platform for Mediterranean Countries along the east-west and north-south corridors and to improve the capacity of Italian regions to manage international cooperation programs on transport and logistics, finally, to support regional entrepreneurship in the foreign services sector.