Scientific publications

PhD thesis

1. Univ. Lyon

   Study of the choice behaviour of travellers in a transport network via a “simulation game”

   González Ramírez, H.

   LICIT - Laboratoire d’Ingénierie Circulation Transport, Univ. Lyon, ENTPE, IFSTTAR Jun 2020

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   The objective of this thesis is to find route choice models that scale-up at network level, i.e., models that predict the choices of travellers over the diversity of situations found in a transport network. The approach is to investigate travellers’ behaviour in transportation networks through computer-based experiments at large scale, for which a platform named the Mobility Decision Game (MDG), has been developed. The MDG permits to observe the choices of the participants on a diverse set of scenarios (OD pairs and routes) with varying traffic conditions and travel time information. The experiments focus on the route choices of uni-modal car trips that are based on the map of the city of Lyon, France. To attain the objective of this thesis, firstly a methodology to find OD pairs that are representative of the network is proposed. The representative OD pairs are used in route choice experiments to obtain choice models that generalise to the various OD configurations in the network. Secondly, the choices of participants in the experiments are analysed from the rational and boundedly rational behaviour perspectives, in order to establish the principle that best describe their choices. Finally, the choice models are assessed in terms of their predictive accuracy. This thesis is part of a European ERC project entitled MAGnUM: Multiscale and Multimodal Traffic Modeling Approach for Sustainable Management of Urban Mobility.

Journal articles & conferences

1. Roy. Soc.

   A paradox of traffic and extra cars in a city as a collective behaviour

   Prieto Curiel, R.,  González Ramírez, H., Quiñones Domínguez, M., and Orjuela Mendoza, J.P.

   Royal Society Open Science Jun 2021

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   Promoting walking or cycling and reducing cars’ use is one of the city planners’ main targets, contributing to a sustainable transport method. Yet, the number of vehicles worldwide is increasing as fast as the population, and motorized mobility has become the primary transport method in most cities. Here, we consider modal share as an emergent behaviour of personal decisions. All individuals minimize their commuting time and reach an equilibrium under which no person is willing to change their transportation mode. In terms of the minimum travel time, the best-case scenario is used to determine the extra commuting time and the excess cars, computed as a social inefficiency. Results show that commuting times could increase up to 25% with many more vehicles than optimum. Paradoxically, all individuals trying to minimize their time could collectively reach the maximum commuting times in the extreme case, with all individuals driving during rush hour.

2. Sci. Rep.

   Vaccination strategies against COVID-19 and the diffusion of anti-vaccination views

   Prieto Curiel, R., and González Ramírez, H.

   Scientific Reports Mar 2021

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   Misinformation is usually adjusted to fit distinct narratives and propagates rapidly through social networks. False beliefs, once adopted, are rarely corrected. Amidst the COVID-19 crisis, pandemic-deniers and people who oppose wearing face masks or quarantine have already been a substantial aspect of the development of the pandemic. With the vaccine for COVID-19, different anti-vaccine narratives are being created and are probably being adopted by large population groups with critical consequences. Assuming full adherence to vaccine administration, we use a diffusion model to analyse epidemic spreading and the impact of different vaccination strategies, measured with the average years of life lost, in three network topologies (a proximity, a scale-free and a small-world network). Then, using a similar diffusion model, we consider the spread of anti-vaccine views in the network, which are adopted based on a persuasiveness parameter of anti-vaccine views. Results show that even if anti-vaccine narratives have a small persuasiveness, a large part of the population will be rapidly exposed to them. Assuming that all individuals are equally likely to adopt anti-vaccine views after being exposed, more central nodes in the network, which are more exposed to these views, are more likely to adopt them. Comparing years of life lost, anti-vaccine views could have a significant cost not only on those who share them, since the core social benefits of a limited vaccination strategy (reduction of susceptible hosts, network disruptions and slowing the spread of the disease) are substantially shortened.

3. TBS

   Assessing traveler compliance with the social optimum: A stated preference study

   Mariotte, G., Leclercq, L.,  González Ramírez, H., Krug, J., and Bécarie, C.

   Travel Behaviour and Society Apr 2021

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   The development of Advanced Traveler Information Systems (ATIS) with en-route navigation systems has opened the door to new traffic regulation policies such as collective route guidance based on social costs, i.e. routes that minimize total travel time. However, a critical element for their efficiency is the compliance of travelers with route recommendations. It is well established that the social optimum is different from user equilibrium, where users drive on their shortest path. Thus, even when knowing that recommendations are for the common good, users may still choose not to follow the guidance given and drive as they wish. In this paper, we use a stated preference survey based on route choice situations from a real network to investigate traveler compliance for different levels of travel time sacrifice vs several social benefits. Two kinds of social benefits are considered: congestion alleviation and emission reduction. The data collected allows us to precisely quantify the travel time sacrifice that a given proportion of travelers would be ready to accept in order to take a different alternative that has a given level of social benefit. In line with the literature, our analysis confirms the decrease of compliance with the increase of sacrifice. Moreover, it suggests that the way the recommendation is intended could play a significant role in the level of compliance: the display of an advice message for the social path (in the congestion alleviation case) is shown to be more efficient than only showing additional information (in the emission reduction case).

4. TBS

   Travel time and bounded rationality in travellers’ route choice behaviour: A computer route choice experiment

   González Ramírez, H., Leclercq, L., Chiabaut, N., Becarie, C., and Krug, J.

   Travel Behaviour and Society Jan 2021

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   Recent empirical studies have found that travellers route choices deviate from perfect rationality, showing that urban trips do not necessary follow the shortest-time routes. However, there is no consent on how much the travellers’ route choice behaviour deviates from the perfect rational assumption. The objective of this study is to contribute to the understanding on how travellers process travel time when making route choices, and to quantify to what extent users are strict travel time minimisers or if bounded rationality is observed. The question of whether travellers evaluate travel time differences in absolute or relative terms is also addressed, and the heterogeneity in the route choice behaviour of travellers investigated. The results of route choice experiments, focused on the choices in diverse OD pairs and traffic conditions, are analysed. In total, 496 participants recorded 5535 choices over 41 OD pairs. It was found that travellers evaluate relative rather than absolute differences in travel time. In 60.5% of the trips participants chose the fastest route, but this percentage is 80% when the travel time between the fastest and the rest of the alternatives is at least 30% higher. Only 10% of the individuals chose the fastest route in all trips, confirming the hypothesis of bounded rationality. Participants exhibited heterogeneous travel time indifference bands: the average participant was indifferent to relative travel time differences of less than 31%. A mixed logit model (MXL), considering heterogeneous indifference bands is proposed. The model shows a similar predictive accuracy compared to the classical MXL model.

1. PLOS One

   Unravelling travellers’ route choice behaviour at full-scale urban network by focusing on representative OD pairs in computer experiments

   González Ramírez, H., Leclercq, L., Chiabaut, N., Becarie, C., and Krug, J.

   PLOS ONE Nov 2019

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   In a city-scale network, trips are made in thousands of origin-destination (OD) pairs connected by multiple routes, resulting in a large number of alternatives with diverse characteristics that influence the route choice behaviour of the travellers. As a consequence, to accurately predict user choices at full network scale, a route choice model should be scalable to suit all possible configurations that may be encountered. In this article, a new methodology to obtain such a model is proposed. The main idea is to use clustering analysis to obtain a small set of representative OD pairs and routes that can be investigated in detail through computer route choice experiments to collect observations on travellers behaviour. The results are then scaled-up to all other OD pairs in the network. It was found that 9 OD pair configurations are sufficient to represent the network of Lyon, France, composed of 96,096 OD pairs and 559,423 routes. The observations, collected over these nine representative OD pair configurations, were used to estimate three mixed logit models. The predictive accuracy of the three models was tested against the predictive accuracy of the same models (with the same specification), but estimated over randomly selected OD pair configurations. The obtained results show that the models estimated with the representative OD pairs are superior in predictive accuracy, thus suggesting the scaling-up to the entire network of the choices of the participants over the representative OD pair configurations, and validating the methodology in this study.

2. CEUS

   Temporal and spatial analysis of the media spotlight

   Prieto Curiel, R., Cabrera Arnau, C., Torres Pinedo, M.,  González Ramírez, H., and Bishop, S. R.

   Computers, Environment and Urban Systems May 2019

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   Items featured in the news usually have a particular novelty or describe events which result in severe impact. Here, the length of time that a story remains in the media spotlight is investigated as well as the scaling with population size of the amount of attention that the media gives to stories from different cities. Based on Twitter feeds, the media coverage from the major online newspapers in Mexico is analysed over a period either side of a recent powerful earthquake. The amount of coverage given to earthquake-related stories had an initial peak and then exhibited an exponential decay, dropping by half every eight days. Furthermore, the coverage per person usually exhibits a superlinear scaling with population size, so that stories about larger cities are more likely to appear in the news. However, during the immediate post-earthquake weeks, the scaling was no longer superlinear. The observed trends can be interpreted as a fundamental switch in the emergent collective behaviour of media producers and consumers.

1. PLOS One

   A novel rare event approach to measure the randomness and concentration of road accidents

   Prieto Curiel, R.,  González Ramírez, H., and Bishop, S.

   PLOS ONE Aug 2018

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   Background Road accidents are one of the main causes of death around the world and yet, from a time-space perspective, they are a rare event. To help us prevent accidents, a metric to determine the level of concentration of road accidents in a city could aid us to determine whether most of the accidents are constrained in a small number of places (hence, the environment plays a leading role) or whether accidents are dispersed over a city as a whole (hence, the driver has the biggest influence). Methods Here, we apply a new metric, the Rare Event Concentration Coefficient (RECC), to measure the concentration of road accidents based on a mixture model applied to the counts of road accidents over a discretised space. A test application of a tessellation of the space and mixture model is shown using two types of road accident data: an urban environment recorded in London between 2005 and 2014 and a motorway environment recorded in Mexico between 2015 and 2016. Findings In terms of their concentration, about 5% of the road junctions are the site of 50% of the accidents while around 80% of the road junctions expect close to zero accidents. Accidents which occur in regions with a high accident rate can be considered to have a strong component related to the environment and therefore changes, such as a road intervention or a change in the speed limit, might be introduced and their impact measured by changes to the RECC metric. This new procedure helps us identify regions with a high accident rate and determine whether the observed number of road accidents at a road junction has decreased over time and hence track structural changes in the road accident settings.

2. TRB

   A massively multiplayer simulation game framework to study dynamic route choice behavior

   González Ramírez, H., Leclercq, L., Chiabaut, N., Becarie, C., and Krug, J.

   In TRB’18, 97th Annual Meeting of the Transportation Research Board Jan 2018

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   In this work, we introduce a novel simulation game platform to study the route choice behaviour of travellers. A unique feature of this game is that it interacts with a microscopic simulator, which is in charge of reproducing the traffic conditions over real road networks, such as Lyon-Villeurbanne (36km2 and 3,222 nodes). Multiple OD pairs can be assigned to players during one game session. The participants play trips changing their departure times and routes, and thus modifying the original assignment of the simulation in real-time. Thus, the simulation game permits to investigate not only the determinants of player decisions (travel time, characteristics of the alternatives, traffic information), but also how concomitant decisions from multiple players impact the network.