An optimization framework for exclusive bus lane allocation in large networks with dynamic congestion

Road space distribution among multiple modes of transport in urban networks has attracted the interest of several researchers and policy planners. Traditionally, these problems are solved by ignoring operational and dynamic characteristics of multi-modal congestion due to the computational burden involved. Revealing the relation between road space share and global performance of the network can lead to more efficient transport system design. The introduction of dedicated bus lanes in some parts of the network has been proposed as a measure to allow high occupancy vehicles to travel through regions with high traffic load without long delays. In this way, the bus transit system operates more efficiently and is competitive to the private car option in terms of travel time. This effect can stimulate a significant mode shift from car to bus and help alleviate congestion by reducing the number of low occupancy vehicles. In this work we address the problem of optimal allocation of exclusive bus lanes in a multi-modal urban network of fixed total road infrastructure and passenger demand, with the aim of minimizing the total passenger hours travelled (PHT) for all travel modes, within a framework which is consistent with the dynamics of congestion. A queueing theory based traffic flow model with proper treatment of spillbacks and traffic signal settings, known as the Store-and-Forward (SaF) model, is extended to simulate the dynamics of congestion inside the network by keeping track of the queues inside all links over time. The SaF simulation model can be used to evaluate the performance of different allocation policies.

A complex networks approach to traffic flow theory: measures and models

Leonardo Bellocchi

In this thesis, we developed a research direction that combines the theoretical concepts of complex networks with practical needs and applications in the field of transportation engineering. As a first objective we analyzed the phenomenon of congestion propagation in a city trying to synthesize - hence reproduce - dynamical systems of complex nature in a well-established and elegant mathematical-physical structure. With this perspective, we identified in the reaction-diffusion-like system the most natural way to describe how congestion spreads in the road networks according to elementary diffusion mechanics (linear) and self-enhancement of traffic jam (non-linear). This analysis showed that models with a small number of parameters can reproduce dynamic network patterns without the need for very detailed and accurate input data. Another topic we dealt with was to indicate centrality measures expressively defined for congested road networks. Inspired by classical complex networks theory, we defined more suitable and exploitable indices in the field of transport and urban mobility that consider in a dynamic framework both the network topology and the spatial distribution and magnitude of congestion. For this scope, we proposed the definition of dynamical efficiency for single and multi-layer networks. Dynamical efficiency responds adequately to the need for classification of urban areas based on their accessibility and on the influence that traffic has, region-par-region, on the average travel time of passengers. This measure combines and exploits local information (average road speeds, functional type) with the complex structure of the road network and the opportunity for convenient alternative routes. Furthermore, by generalizing the dynamical efficiency definition in a multimodal environment, we are able to identify the most attractive intermodal exchange stations (for example, bus-metro, private car-public transport) and estimate their optimal capacity service. This opens up the workspace for innumerable engineering applications and accurate evaluations of the impact of high traffic demand in each transport system. Among the same lines, another chapter of this thesis concerns a measure of simplicity for paths and allows us to study an extended database of real trajectories and classify the drivers according to their priority path choice factors. Finally, we studied the congestion propagation under a topological perspective as an aggregation of connected components of congested links. By analyzing the distribution of their sizes and the average merging rate we are be able to (i) point out important premonitory signals that anticipate imminent traffic jam (namely morning and evening peak-hours), (ii) to visualize the most critical bottlenecks and (iii) to better understand the causal inference between components of congestion and the average network speed.

EPFL2020

Public Urban Transport, Mobility Patterns and Social Exclusion

Regina Witter

What are the social impacts of a new, less efficient public transport system in a city that is known for its inequality concerning access to daily activities and participation in urban life? More precisely, what are the implications of a re-regulated transport system, if the city has previously gone through a long period of deregulation? Are the changes limited to altered accessibility conditions, or are there further consequences for people's travel competencies, habits and mobility patterns? And what does that mean for the dissolution or manifestation of social inequality and risks of social exclusion? With a specific regard to these interests, this work specifically focuses on the case of Santiago de Chile. There the public transport policy passed from a period of complete de-regulation in the 1970s and 1980s to a period of re-regulation as of the 1990s. During the deregulation period, the services had been characterized by an uncoordinated oversupply of private busses that existed in parallel to the more expensive public metro. In order to suspend the stigmatization of bus-based transport as the 'mode for the poor', the sophisticated 'Transantiago' bus system was implemented in February 2007, which was modelled of the famous BRT system 'Transmilenio' in Bogotá. The Transantiago project included the total re-design of the network system and the private operating companies at one glance. It introduced new vehicles and infrastructures as well as an electronic ticketing system that combined the bus and metro systems in a tariff union. Unfortunately, the ambitious project failed, due to various political, technical and social reasons. Up until today, the acceptance and satisfaction of the inhabitants with Transantiago have been rather low. Being aware of the importance of the technical problems, this study concentrates on the social problems and the related impacts Transantiago has had on people's daily life. The research is done on the basis of three hypotheses that are strongly based on the concept of 'motility', i.e. the potential to be mobile, including the set of factors which enable spatial mobility (access, competencies and appropriation). The hypotheses are tested on the basis of a mixed approach that combines various qualitative methods with an 'ad-hoc' survey of 2000 households in five different areas of the metropolitan Santiago area. The survey results are analysed on the basis of various spatial and statistical procedures, including, among others, structural equation modelling. We first consider the relation between the differences related to mobility and the social differences during the period of deregulation and describe the major mobility patterns and habits developed during that time (hypothesis 1). Then we come to the Transantiago failures and the changes imposed on people's accessibility conditions, travel competencies, preferences and habits (hypothesis 2). Finally we also explore the impact the Transantiago system has had on people's daily life, more precisely on people's daily activities and the activity locations as well as the main travel modes used to reach these locations. Comparing people's current activity patterns and travel patterns with those of the deregulated transport period, we intend to reveal if Transantiago has aggravated or alleviated existing mobility inequalities and related risks of social exclusion (hypothesis 3). The results show that mobility patterns developed during the deregulated period have had a strong negative impact on people's ability to get used to and accept the sophisticated Transantiago system. Particularly people of low income, people of a lower education level, people without access to a private car and people who live in peripheral areas and don't have direct access to the metro were most heavily impacted. Sometimes, older people and women within these groups suffered more than younger adults and men. The initial difficulties have had a negative impact on the current evaluation and image of public transport, and on the other hand they have exacerbated already existing risks of social exclusion and segregation. Especially the more 'vulnerable' inhabitants have adapted their daily activity patterns and travel patterns. They travel less for job-related and leisure-related purposes; they prefer other modes to bus-based public transport and remain often closer to their place of residence than before the Transantiago implementation. Nonetheless, Transantiago has also had some positive impacts such as increased spatial mobility for inhabitants with direct access to the metro, low travel expenditures due to permanent operating subsidies as well as reduced environmental emissions and safety problems. After all, it is hardly possible to definitively determine if the current mobility-related and social inequalities are effectively a consequence of the Transantiago system. It is also unclear if these inequalities have today a more widespread impact than during the deregulated transport period. In general, throughout this study the important influence of income and social status on inhabitants' mobility conditions and travel behaviour is revealed. Alternative concepts related to residential preferences and urban lifestyles turn out to be less pertinent to the explanation of social differences in travel behaviour. This also means that transport policy aimed at equal mobility conditions can only give a contribution to social inclusion. Therefore, additional urban and social measures are needed. This work consists of six parts. Following the introduction (chapter 1), a broad theoretical framework is presented where the different topics of interest are discussed and examples of empirical studies are presented, with a focus on emerging economies (chapter 2): transport regulation and deregulation and recent trends in public transport policy and supply (2.1); the various spatial, social and individual determinants of travel behaviour and mobility patterns and the implications for transport research (2.2); mobility inequality as possible source of social exclusion, which calls for transport policy making with a focus on social equity (2.3). After having presented the research hypotheses and the methodology employed (chapter 3), the case study area of Santiago is introduced. In this context we describe the development from the deregulated transport period up until today with regard to four issues: the spatial and social structure of the city as well as the development of transport policy and people's mobility patterns (chapter 4). Each of the three hypotheses is analysed and evaluated on the basis of the own empiric works (chapter 5). The work concludes with a synthesis as well as some final remarks and implications for the development of transport policy in Santiago and other cities in emerging economies, where comprehensive transport changes are envisaged (chapter 6).

EPFL2012

Network design of a transport system based on accelerating moving walkways

Michel Bierlaire, Iliya Dimitrov Markov, Riccardo Scarinci

Pollution, congestion and urbanistic considerations are leading to a change in the use of private vehicles in dense city centers. More frequently, the last-mile is covered with systems such as public transport, car sharing and bike sharing as well as an increase in walking and cycling. Following this trend, we assume a hypothetical scenario where the use of private cars is strongly limited in dense urban areas, and innovative transport modes must be used. This work investigates a futuristic system based on a network of accelerating moving walkways (AMW) to facilitate the movement of pedestrians in city centers where cars have been banned. Unlike constant speed moving walkways, AMWs can reach speeds of up to 15 km/h thanks to an acceleration section. This paper presents a rigorous description of the system characteristics from a transportation point of view, develops a heuristic algorithm for the network design problem, and tests it on a real case study. Given a network of urban roads and an origin-destination demand, the optimization algorithm, which combines traffic assignment and supply modification, explores the trade-off curve between the total travel time and capital cost of the infrastructure. The results give practical insight on the possible dimensioning of the system, show the optimal network designs, and how these vary with a reduction of the available budget. This paper investigates for the first time the use of AMWs at a network scale, and provides results useful for analyzing the system feasibility. The results on travel time, investment budget and payback period indicates that AMWs could be an effective mode of transport in cities. (C) 2017 Published by Elsevier Ltd.