Ana Bastos Silva

Turboroundabouts: Multicriterion Assessment of Intersection Capacity, Safety, and Emissions

A “turboroundabout” is a variation of the conventional multilane roundabout in which spiral road markings and raised lane dividers force drivers to follow a specific path according to their intended destination. This geometry eliminates weaving and cut-in conflicts by guiding drivers continuously from entry to exit. Turboroundabouts were conceived with the main aim of improving safety, but their practical benefits are relatively unknown. Likewise, the few existing studies on turboroundabouts do not allow definitive conclusions to be drawn about the delay and emissions performance characteristics of turboroundabouts; further research is needed. This research focused on the use of appropriate modeling methodologies to understand the effects of turboroundabouts on capacity, safety, and emissions in comparison with the effects of conventional single-lane and double-lane roundabouts. The results indicate that turboroundabouts have capacity levels comparable to those of two-lane roundabouts but are less robust concerning the directional split of the entry traffic; turboroundabouts lead to fewer traffic conflicts, but the traffic conflicts that do occur are more severe. The results also show that the implementation of turboroundabouts provides no advantages for emissions when the main concerns are carbon dioxide and oxides of nitrogen.

Hybrid calibration of microscopic simulation models

This chapter presents a procedure to calibrate the Gipps car-following model based on macroscopic data. The proposed method extends previous approaches in order to account for the effect of driver variability in the speed–flow relationships. The procedure was applied in a real calibration problem for the city of Coimbra, Portugal, as part of a broader calibration framework that also includes a conventional optimization based on a genetic algorithm. The results show that the new methodology is promising in terms of practical applicability.

Validation of the Surrogate Safety Assessment Model for Assessment of Intersection Safety

The surrogate safety assessment model (SSAM) is a software application that reads trajectory files generated by microscopic simulation programs and calculates surrogate measures of safety. This approach eliminates the subjectivity associated with the conventional conflict analysis technique and allows assessment of the safety of a facility under a controlled environment before accidents occur. The specific goal of this research was to validate SSAM as a tool for accident prediction at urban intersections. Two methods were used for validation. The first method compared the simulated number of conflicts from the use of SSAM and the predicted number of injury accidents from analytic models in three reference intersection layouts (four-leg priority intersection, four-leg staggered intersection, and single-lane roundabout). The second method compared SSAM results with conflicts observed on site in four real intersections: two priority ones and two roundabouts. The results indicate that, despite some limitations related to the nature of current traffic microsimulation models, SSAM analysis is an extremely promising approach to assessing the safety of new facilities or innovative layouts.

Setting speed limits in interurban single-carriageway highways using expert’s judgment

AbstractUntil recently, the design of road infrastructure involved mainly concerns related to the base speed value and to requirements ensuring a high level of service. Currently, it is widely accepted that only an integrated approach is able to take into account the interests and needs of all the involved stakeholders, namely the need of traffic fluidity by motor vehicles, and quality of life and safety associated to other users and local residents. This vision has been leading to different speed management approaches, particularly in relation to the setting of the appropriate and coherent speed limits along extensive routes. In this context, this study is part of a broader research program aimed to develop a methodology of speed management with a widespread use applied to single carriageway roads in interurban areas, crossing different road surrounding environments with varying rural, urban or mixed characteristics. More specifically, this research line is focused on the development of a decision-suppor...

Efficient Solutions for Urban Mobility - Policies, Strategies and Measures

Over the past few decades, particularly in urban areas, mobility needs have significantly grown and changed as a result of the normal social and economic development. The mobility is nowadays a very diverse and complex reality, in reason of the tendency for a more disperse residential occupation and for a more decentralized location of most commercial and service activities, as well as of different population mobility habits resulting from their increased wealth. As a consequence urban mobility has been ever more dependent on the private car and, in many cases, by the existence of inefficient and costly public transport systems, with obvious negative impacts at the environmental, social and economic levels for the society as a all. It is also relevant to refer that in some European Union (EU) countries transports use up to 30% of the energy used by the different human activity sectors and is responsible for 25-30% of the total of greenhouse gases (EEA, 2000; Civitas, 2006), with the car being responsible for as much as 50% of the emissions produced by passenger transport systems. It is also important to notice the negative impacts that transport systems can, and often have, over several quality of life aspects. In many cases these systems invade many of the cities public spaces, which are otherwise used in many other activities such as leisure. This situation has led to an increased emphasis being placed in the development of transport strategies and solutions within the Sustainable Development Global Agenda (Commission of the European Communities, 2006). The EU Green Paper over Urban Environment, the EU Treaty, the successive EU environment and transport action programs, the Rio de Janeiro UN Conference on Environment and Development or the different UN conferences culminating with HABITAT II, constitute some of the initiatives witch have been raising the sustainability issue and, in this context, have been discussing the future of urban mobility. An urban strategic planning process, taking into consideration the urban area fundamental characteristics and its population needs, is thus an essential framework for the identification of adequate sustainable transport policies. These planning processes can vary significantly but generally it can be said that they are evermore inter-disciplinary and focused mainly on two different but complementary areas. 12