Clément Poirier
email: clement.poirier@ifsttar.fr

Sonia Adelé

Jean-Marie Burkhardt

Individual accidents at the interface between Platform, Train and Tracks (PT 2 I) in the subway: a literature review

The subway context is a risky environment. Hundreds of individual incidents occur every year in this environment, entailing a safety issue for subway companies and safety organizations. This review deals with individual incidents at the platform-train-tracks interface (PT²I) with a particular focus on accidents and precursor analysis and on preventive measures. 42 articles ranging from 1984 to 2018 were selected and analysed to understand this issue. Our results suggest that the existing literature provides a relatively comprehensive picture of the individual factors involved in accidents, but that there is a lack of knowledge on the impact of the socio-cultural environment, the equipment and surroundings, and the organisational factors. Concerning preventive measures, although 19 measures covering all levels and types of prevention are presented, only 6 have been evaluated. Research areas of particular interest are real user behaviours, systemic approaches to behavioural determinants, and evaluations of preventive measures.

Introduction

Subway networks have developed continuously ever since the first one was built in London in 1863, and they currently serve many of the world's major cities [START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF]. In 2017, there were 178 subway systems distributed in 56 countries. They transported 53,768 million passengers in the world. In the six years between 2012 and 2017, ridership grew globally by 19.5% (UITP 2018). Four main types of subway infrastructures exist worldwide: stations are mostly underground (67%), elevated (20%) or at-grade (12%) while in-trench stations (1%) are uncommon (UITP 2018).

Subway networks experience several incidents and accidents, some of them resulting in injury or death to both staff members and to users. The most widely publicized accidents are those involving a large number of casualties, such as the derailment of a train in Chicago in 2014 (30 injured) or in Moscow the same year (21 fatalities and more than 160 injured).

Globally, however, subway networks have recorded very few collective accidents, (i.e accidents implying multiple victims), and those that have occurred have caused few casualties; individual incidents and accidents are largely predominant. For example in France, subway companies report annually more than 1,200 individual safety incidents on their systems (STRMTG 2018) although most of them did not result in any severe consequences for humans. These incidents resulted on average in more than 10 fatalities and 700 injuries per year over a five-year period (STRMTG 2017) while twenty-eight suicide-related deaths occurred on average each year between [START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF]and 2015(STRMTG 2017)). The London Underground reported on average about 3,000 incidents each year including assaults, slips, on board injuries, etc. (e.g. LUL 2019), that resulted in about 40 deaths per year of voluntary or involuntary origin between 2000 and 2010 [START_REF] Martin | Suicide patterns on the London Underground railway system, 2000-2010[END_REF].

In addition to the human loss, subway accidents cause trauma and work-related stress to the rail staff and rescue employees, severe consequences for train drivers (e.g. somatic problems, anxiety, sleep disruption, etc.) as well as for passengers and eyewitnesses [START_REF] Havârneanu | A systematic review of the literature on safety measures to prevent railway suicides and trespassing accidents[END_REF]. Subway drivers who experienced a "person under train" (PUT) event had higher sick leave absenteeism, smoking habits and alcohol habits, and these problems worsened when the victims when the victims were severely injured [START_REF] Theorell | Person under train' incidents from the subway driver's point of view-A prospective 1-year follow-up study: The design, and medical and psychiatric data[END_REF].

The platform-train interface (PTI) has been identified for a long time as a hotspot of individual injuries and fatalities in subway networks [START_REF] Santoso | How Safe is the Rail Platform? A Study of Bangkok Mass Transit System (BTS)[END_REF]. This interface encompasses the train door and the corresponding adjacent spaces on the platform and on the trains, and includes any devices and information provided to the passengers during their interactions in this phase of their trip. Passenger interactions are mostly concerned with moving, waiting, boarding and alighting. In fact, since the tracks are also a critical component in relation to injuries and fatalities, it would be more correct to refer to the platform-traintracks interface (PT²I) rather than to the platform-train interface (PTI).

The aim of this paper was to review research on individual accidents 1 leading to injuries and fatalities at the PT²I with a focus on their individual, contextual, spatio-temporal and behavioural determinants, as well as on existing and prospective means to prevent their occurrence. It updates and extends two previous literature reviews. The review by [START_REF] Gershon R R M | Health and Safety Hazards Associated with Subways: A Review[END_REF] covered all subway hazards (including crimes) without much detail on subway accidents and was not specific to the PT²I. We share three references [START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF][START_REF] O'donnell | The epidemiology of suicide on the London underground[END_REF][START_REF] Sonneck | Imitative suicide on the Viennese subway[END_REF] with this review and have added 39 references mostly posterior to 2005. The review by [START_REF] Havârneanu | A systematic review of the literature on safety measures to prevent railway suicides and trespassing accidents[END_REF] concentrated on the prevention of accidents and suicides in the railway context with some marginal references to the subway context. Furthermore, [START_REF] Havârneanu | A systematic review of the literature on safety measures to prevent railway suicides and trespassing accidents[END_REF] did not review the knowledge about user behaviours and other determinants associated with accidents. Our review includes this topic and shares six references [START_REF] Coats | Effect of station design on death in the London Underground: observational study[END_REF][START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF][START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF][START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF][START_REF] Niederkrotenthaler | Predictors of Suicide and Suicide Attempt in Subway Stations: A Population-based Ecological Study[END_REF]O'Donnell andFarmer 1992, 1994).

It is not easy to conduct a literature review on accidents as no international standardized classification of individual accidents in subways has been adopted. Thus, research dealing with accidents is not fully comparable. Moreover, current knowledge on victims' profiles, the context of accidents (e.g. time, location) and their determinants is sparse and scattered throughout the literature. User behaviour at the PT²I is sparsely documented and poorly understood, especially in relation to the occurrence of individual accidents. Furthermore, some of our references include information about both accidents and suicides for the following reasons, although the literature search did not include keywords related to suicide or incidents. First, the way in which injuries or fatalities are classified as accidents or suicides is not always clear or consistent across the different sources. While the presence or 1 The term accident will be used exclusively to describe events that led to unintentional injury or death. The term suicide is used when injuries or deaths due to intentional events (excluding crimes), suicide attempts are included. The term incident will be used to all types of events (accidents, suicides, crimes). absence of intent to kill oneself is the common criterion to distinguish between suicides and accidents [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF]), this intention is not always easy to determine. Second, most of the existing references address fatalities and injuries either in an undifferentiated manner [START_REF] Coats | Effect of station design on death in the London Underground: observational study[END_REF][START_REF] Cocks | Study of 100 patients injured by London underground trains 1981-6[END_REF][START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF][START_REF] O'donnell | The epidemiology of suicide on the London underground[END_REF] or separately [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Uittenbogaard | Temporal and spatial patterns of suicides in Stockholm's subway stations[END_REF]. Finally, existing preventive measures may, in some cases, apply to both suicides and accidents. This review is split in four parts. We first present the method used to select, classify and analyse the articles. The second part is dedicated to the two-step analysis of the articles.

The quantitative analysis covers the country and time distribution, the methodologies used and the types of data in each article. The qualitative analysis addresses two main topics: accident analysis/description and prevention. The last part discusses the contributions of existing research in order to identify gaps that need to be filled in future research.

Method

This review used a three-step methodology based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement [START_REF] Moher | Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement[END_REF]) (Fig. 1). The search was applied to title, keywords and abstract using the following terms: "Metro" or "Subway" or "Underground" completed with "Injur*" or "Fatalit*" or "Accident*". In addition, we also looked at the "grey literature" such as practical safety guidance documents, conference proceedings, accident reports, statistical reports, and official publications of subway companies. Several subway companies, as well as national and international administrations, publish reports on safety, incidents, and the organisation of subway systems on their own websites. This step resulted in 4,289 references.

We read through all the titles and abstracts. To be included, the document had to provide evidence about the subway system, station design and user behaviours, safety performance of measures dedicated to the subway, or subway accidents. This process resulted in a subset of 126 documents, of which 22 were not included because we could not access to the full document (e.g. unpublished conference presentation) or only the summary was written in English or French.

The content of the remaining 104 documents was analysed in depth to determine their eligibility. To be included, references needed to address at least one of the following themes: 1) preventive measures against PT²I incidents (suicides or accidents), 2) users' behaviours at the PT²I, 3) precursors of PT²I incidents, 4) victimology (context and victims' profiles) on PT²I incidents. We obtained 42 articles that met these criteria. Our analytical approach was twofold. We first carried out a quantitative synthesis of the 42 eligible publications using the following descriptive schema: 1) type of publication (conference proceedings or journal article), 2) country and year of publication, 3) main topic (prevention or accident), 4) type of data (empirical, theoretical or technical), 5) methodology used, 6) preventive measures (none, proposed, or evaluated). Second, we conducted a content analysis, adopting a qualitative perspective on accidents, the description and explanation of human behaviour at the PT 2 interface, existing evidence related to general and specific preventive measures proposed by different authors, and possibly unique measures to prevent individual incidents and accidents in subway networks.

Results

Quantitative analysis

This first section describes the 42 selected papers published between 1984 and 2018 based on the criteria mentioned above. Most of the publications come from scientific journals (n=34), the rest from conference proceedings (n=8). The scientific journals are all peerreviewed and correspond to Q1 or Q2 in the SCIMAGO classification. All the conference papers except the one by [START_REF] Zhou | Causal Analysis to a Subway Accident: A Comparison of STAMP and RAIB[END_REF] were presented at international conferences based on a peer-reviewed selection process.

Spatial and temporal distribution of our corpus

The data used in these publications usually came from a single country although three documents reported on data and results within an international scope [START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF]2013;[START_REF] O'donnell | Suicidal acts on metro systems: an international perspective[END_REF]. Most of the papers came from three regions (Table 1): Asia (n=16) followed by Europe (n=12) and North America (n=9). Less well represented areas were Latin America (n=2) and the Middle East (n=1). The most represented countries were China (n=10), the United-States (n=6) and the United Kingdom (n=5). Other countries had less than four publications. The number of publications increased between 1984 to 2018 (χ² (2, N=42)=19.5; p<.01) (Table 1) with the development of Asian research on this topic, in line with the growth of subway networks in this area.

Table°1 Distribution of references by country and time period

World region

Country Time Period Tot.

Topic evolution: accident description vs. preventive means

All the publications were classified according to the main topic they addressed, either prevention (n=18) or accidents and precursor analysis/descriptions (n=24) (Table 2). They were classified as oriented towards prevention when most of the text was about the design and/or evaluation of one or more preventive measures against individual accidents at the PT²I. They were classified as accident analysis when the text was mostly oriented towards describing the characteristics of accidents and victims (toxicology, location, time, etc.) or investigating some accident precursors such as user behaviours, knowledge or perception of risk at the PT²I. It is worth noting that preventive measures were sometimes mentioned in papers oriented towards accident analysis, but usually in a marginal and cursory manner, for example as a suggestion for possible preventive solutions in the conclusion or discussion section. Accident reports were the main topic in the literature on subway issues before 2007.

After this date, prevention and accidents were given equal importance. The temporal evolution of these two topics was the same (χ²(2, N=42)=0.9; p<n.s).

Nature of contributions and methods used

Three types of papers can be distinguished according to the nature of the evidence on which they are grounded: empirical, technical and theoretical contributions (Table 2).

Empirical studies

Empirical papers are based on the collection and analysis of data from the field or from the laboratory through observation, experiments, surveys or accident/incident reports.

Various data collection and analysis methods are used, and sometimes combined, in our subset of 35 empirical papers.

Descriptive analysis (n=26) refers to the analysis of data on accidents, fatalities and incidents from different sources (police, medical services, transport agencies, subway operator reports).

Questionnaires were used with one or two target populations: professionals (n=3) and users/passengers (n=6). Various topics were investigated: the perception of platform safety and risky behaviours [START_REF] Santoso | How Safe is the Rail Platform? A Study of Bangkok Mass Transit System (BTS)[END_REF][START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF][START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF], the risk of accidents in general [START_REF] Kim | Accident risk associated with smartphone addiction: A study on university students in Korea[END_REF], the acceptance of subway incidents [START_REF] Chen | Risk analysis on Beijing metro operation initiated by human factors[END_REF][START_REF] Jones-Lee | Scale and context effects in the valuation of transport safety[END_REF]. Preventive measures were also investigated or described through questionnaires [START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF][START_REF] Santoso | How Safe is the Rail Platform? A Study of Bangkok Mass Transit System (BTS)[END_REF].

Experimental design characterized four papers. Three papers evaluated a preventive measure [START_REF] Duarte | The effect of humoristic vs. dramatic animationbased warnings: A study on acceptance and risk perception[END_REF][START_REF] Muñoz | Alleviating a subway bottleneck through a platform gate[END_REF][START_REF] Yang | Temporary Incentives Change Daily Routines: Evidence from a Field Experiment on Singapore's Subways[END_REF], while the fourth assessed users' perception and beliefs of risks in several scenarios in the PT²I context [START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF].

Observation was reported in only four studies, either as the main (Clarke and Poyner 1984;Zhang et al. 2012) or as a preliminary approach for gathering data [START_REF] Santoso | How Safe is the Rail Platform? A Study of Bangkok Mass Transit System (BTS)[END_REF][START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF]. Three papers used interviews as a pilot study to create questionnaires [START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF][START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF] or to prepare observations (Clarke and Poyner 1984) by listing risky behaviours with participants.

Technical studies

We considered as technical papers (n=5) those that used computer-based simulation instead of studying real users or that described the organizational and technological measures for the prevention of PT 2 I accidents.

Two papers used computer-based simulations to create the station environment with the aim of mimicking passengers' behaviours or testing preventive measures [START_REF] Baee | Passenger Boarding/Alighting Management in Urban Rail Transportation[END_REF][START_REF] Portillo-Villasana G De | Effectiveness of Physical Barriers Installation for Prevention of Incidents in Mexico City's Subway System[END_REF]. Three papers described technical devices for the PT²I [START_REF] Joung | A study on system to reduce the gap between subway vehicle and platform[END_REF][START_REF] Mathew | Using the environment as an interactive interface to motivate positive behavior change in a subway station[END_REF][START_REF] Zhang | Monitoring the gaps between the platform screen doors and the doors of subway train based on optical time domain reflectometer[END_REF].

Literature review

Two papers present literature review about safety in railway contexts (including the subway) in the sense that they are based on assertions about human behaviours and descriptions about subway safety, rather than on the collection and analysis of empirical data. [START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF] proposed a theoretical description and analysis of incidents, focusing on suicides in the railway context (including the subway). [START_REF] Gershon R R M | Health and Safety Hazards Associated with Subways: A Review[END_REF] reviewed the literature about various dimensions of passengers' health and safety in the subway.

Preventive measures found in the corpus

Thirty-eight of the 42 papers mention one or more preventive measures, from which we identified 19 distinct specific measures (Table 3). 1984-1996-2008-1995 2007 2018 Preferential tariff 1(1) 1

These preventive measures were described with various levels of detail and evidence.

Some papers (n=9) proposed only one or more measures, sometimes at a very general level.

Another set of papers reported on some assessments of preventive measures (n=13). A third set proposed and detailed the content of preventive measures without any evaluation (n=12).

A third of these measures (7/20) were subjected to evaluation. Platform screen doors (PSD) (n=4) was the most frequently evaluated measure, followed by suicide pits (n=3), unidirectional gates on the platform (n=2), an accident analysis method (n=2), the presence of surveillance units (n=1), video spots (n=1), and preferential tariffs (n=1).

3.2 Qualitative analysis

Characteristics of incidents and accidents

Fourteen studies investigated the consequences of subway incidents on victims. They used various sources and types of data and examined the issues at various levels of detail (Tables 4, 5 and6).

While some papers focus on fatality records, the others adopt a broader scope and consider patients admitted after a subway-related accident, or incident databases. In the case of incident databases, accidents are often one of the different items surveyed and few, if no, details are given about the context and the explanatory factors. Furthermore, the classification of occurrences is not always consistent between authorities or sources. For example, only a subset of the studies make a clear distinction between intentional (suicide) and unintentional incidents (accidents) [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF][START_REF] Uittenbogaard | Temporal and spatial patterns of suicides in Stockholm's subway stations[END_REF]. This makes it difficult to aggregate outcomes based on existing data because of their lack of consistency and incompleteness. A further difficulty is that subway networks exhibit highly distinctive characteristics depending on the world region, the country and the moment of the study in terms of infrastructure, degree of automation, ridership etc. This means that the outcomes are not applicable between countries or even between regions, as well as over time. In addition, these data are associated with a limited range of identifiable risk factors, and in particular those relative to individual behaviours and motivations.

Four main classes of individual incidents with wide variations in accident and other event rates

The literature identifies up to four main classes of individual incidents depending on the intentionality criterion: accidents, suicides, homicides, and undetermined.

The proportion of subway fatalities (Table 4) classified as accidental ranges from 5% [START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF] in Toronto between 1954and 1980, 11% in Montreal between 1986-1995[START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF] to 47% in the New York city subway between 1990 and 2003 [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]). An even higher rate of 50% of accidents is reported by [START_REF] He | Unnatural Deaths in Shanghai from 2000 to 2009: A Retrospective Study of Forensic Autopsy Cases at the Shanghai Public Security Bureau[END_REF] for the Shanghai subway between 2000 and 2009. However, a particularly low number of fatalities in comparison to any other network characterises the latter. Suicide rates vary in a complementary fashion between 95% to 51% depending on the city and the period. One hypothesis could be that accidents are more prone to occur in large networks with a high ridership (e.g. NY City), whereas a lower prevalence of accidents in smaller subway networks (e.g. Toronto, Montreal or Stockholm) would increase the proportion of suicides. Another explanation may lie in differences related to the stations' infrastructure, the rolling stock and the preventive measures implemented. It is worth noting that the ratio between accidents and suicides differs depending on the sources and the nature of the data (medical reports, death reports, etc.). For example, in New York city, medical records of patients admitted after subway-related injury to Bellevue Hospital show only 17% [START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF] or 25% [START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF]) of suicides whereas an average of 51% of suicides was found when death certificates were consulted [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF]. This may be due to a greater proportion of fatal outcomes in the case of suicides as compared to any other incident.

Depending on the papers, there can be also up to 17% of "undetermined" fatality cases, highlighting that this four-part classification is not straightforward, in particular when information about the person's intention is missing. Finally, homicides represent between 0.2% [START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF] and 0.3% of patients admitted after subway-related injuries [START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF]) and between 2% [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF] and 3% [START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF] of fatalities in North America. Results: The number of suicides was slightly higher on weekdays with a peak in the afternoon (15:00 and 16:00).

Accidents were most frequent during the evening and night and during weekends.

Highest incidence of suicides was in spring and highest incidence of accidents was in autumn and winter.

Highest rates of suicide were observed in the periphery while highest rates of accidents were found adjacent to the city center.

Fatality rate and causes of injury

To the best of our knowledge, and in contrast with other transport modes (e.g. road, rail), there are no published data on death rates and passenger injuries in subway systems at an international level. The few existing sources concern a specific network or a country -over a given period -and provide limited information on the incidence and mortality of passenger incidents in subways. These studies based on incidents and patient records (Table 5) showed a fatality rate between 10% [START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF]) and 57% [START_REF] Coats | Effect of station design on death in the London Underground: observational study[END_REF]. At a wider scale, data from the U.S. subway showed a fatality rate of 0.33 deaths per billion passengermiles between 2000 and 2014. This is higher than the fatality rate for bus transport (transit, intercity, school, charter) (0.2 deaths per billion passenger-miles) but slightly lower than commuter rail and Amtrak (0.36 deaths per billion passenger-miles) and far safer than roads (6.53 deaths per billion passenger-miles) (APTA 2016). Subway-related injuries and fatalities are associated with two main causes: mechanical when a collision occurs and/or electrical when there is contact with the third rail that delivers electrical power to the train. [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF] give the only available evidence regarding the prevalence of these two causes. They report that between 2003 and 2007, most of the 211 fatalities registered in the New York City subway were caused by blunt trauma (98%) and very few by electrocution (2%).

Accidents and suicide-related fatalities differ in their daytime and weekday distribution

The time distribution of fatalities in the subway differs depending on whether they are intentional (suicide) or unintentional (accident) in nature. Data from two networks (New York and Stockholm) show that accidents occur most frequently during the afternoon rush (17:00 to 20:00), in the evening (20:00 to 24:00), and early in the morning (4:00 to 8:00) (Lin and Gill 2009; Uittenbogaard and Ceccato 2015). In addition, there is no difference in the accident rate by day of the week in London, New York and Stockholm subway networks [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF]O'Donnell and Walter 1994;[START_REF] Uittenbogaard | Temporal and spatial patterns of suicides in Stockholm's subway stations[END_REF].

In contrast, the suicide rate (Table 4 and6) is the highest in the middle of the day, i.e.

between 10:00 and 16:00 [START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF][START_REF] Ladwig | Patterns of suicidal behaviour in a metro subway system: A study of 306 cases injured by the Munich subway, 1980-1999[END_REF][START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF] suicide rates are at the beginning of the week, on Monday and Tuesday [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Sonneck | Imitative suicide on the Viennese subway[END_REF]. Results: Suicides occurred the most between 9:00 to 12:00, and most at the beginning of the week and least on Sunday, The sample did not reveal a consistent seasonal pattern. Results: Most incidents occurred in the morning and afternoon rush hours (7:00 to 9:00 and 17:00 to 19:00)

Studies using media records

Distribution of accidents across seasons and places varies depending on the network

Some variations across seasons are specific to the network: whereas the winter is the highest accident-prone period in New York [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF], most accidents are observed in autumn in Stockholm [START_REF] Uittenbogaard | Temporal and spatial patterns of suicides in Stockholm's subway stations[END_REF]. Suicides occur less at the beginning of autumn (September and October) and more in spring and winter on three networks: New York city, London and Stockholm [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Martin | Suicide patterns on the London Underground railway system, 2000-2010[END_REF][START_REF] Uittenbogaard | Temporal and spatial patterns of suicides in Stockholm's subway stations[END_REF]. Conversely, in the Munich subway, the number of deaths due to suicide does not vary with the season [START_REF] Ladwig | Patterns of suicidal behaviour in a metro subway system: A study of 306 cases injured by the Munich subway, 1980-1999[END_REF].

In New York, London and Stockholm, fatalities due to accidents are mainly concentrated in the city centre area while suicides are more frequent in suburban stations [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Uittenbogaard | Temporal and spatial patterns of suicides in Stockholm's subway stations[END_REF] or in proximity to psychiatric hospitals [START_REF] O'donnell | The epidemiology of suicide on the London underground[END_REF].

Victims are predominantly male and middle-aged

Medical and coronary records provide information about the victims' characteristics (Table 4 and6). The study of cohorts of patients admitted after a subway related injury showed that 49 to 80% of them are male [START_REF] Cocks | Study of 100 patients injured by London underground trains 1981-6[END_REF][START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF][START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF].

However, the male/female distribution between accident and suicide victims appears to differ: the victims of fatal accidents in the subway are predominantly male [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] He | Unnatural Deaths in Shanghai from 2000 to 2009: A Retrospective Study of Forensic Autopsy Cases at the Shanghai Public Security Bureau[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF], accounting for 88% on average. When only deaths by suicide are considered, the male-to-female ratio is slightly lower but men still account for the vast majority with on average 66 to 81% [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Martin | Suicide patterns on the London Underground railway system, 2000-2010[END_REF][START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF].

Generally, the age of victims appears to be similar in subway-related accidents and suicide fatalities [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF]. The victims of subway incidents are predominantly middle-aged, with an average age of about 40 [START_REF] Cocks | Study of 100 patients injured by London underground trains 1981-6[END_REF][START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF][START_REF] He | Unnatural Deaths in Shanghai from 2000 to 2009: A Retrospective Study of Forensic Autopsy Cases at the Shanghai Public Security Bureau[END_REF][START_REF] Martin | Suicide patterns on the London Underground railway system, 2000-2010[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF][START_REF] Sonneck | Imitative suicide on the Viennese subway[END_REF].

Alcohol and cocaine are associated with accidents, antidepressants with suicides

Alcohol or drug intoxication is frequently associated with accidents and suicides [START_REF] Gershon R R M | Health and Safety Hazards Associated with Subways: A Review[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF]. [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF] and [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF] report toxicological evidence of drugs in 63% of victims. The substances identified appear to differ depending on the type of incident. In the New York City subway, alcohol was detected on average in 40% of fatal accidents and 15% of suicides [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF][START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF]. In New York, drugs were detected on average in 20% of fatalities (suicides and accidents) but the types of drugs used differ between accidents and suicides. [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF] found that antidepressant medications are more frequently detected in suicides (21% vs. 8% in accidents) whereas cocaine is more frequent in accidents [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF][START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF]. [START_REF] Rodier | Subway-Related Trauma: An Urban Public Health Issue with a High Case-Fatality Rate[END_REF] found that 39% of patients admitted after a subway related injury had a history of psychiatric illness and [START_REF] Cocks | Study of 100 patients injured by London underground trains 1981-6[END_REF] found that 58% of patients injured on the London underground system had a previous history of psychiatric illness. In contrast, [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF] reported differences in the number of victims of subway-related fatalities with psychiatric illness: 34% of suicide victims vs. 3% of accident victims.

Psychiatric and socio-economic characteristics of victims

A few studies have investigated the impact of socio-economic factors on the occurrence of incidents. [START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF] observed that the higher the number of accidents at a station, the higher the unemployment rate in the corresponding area. They found that slightly less than half of 46% of patients admitted after subway injuries in the New York city subway between 1990 and 2003 were unemployed. In the same network, [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF] and [START_REF] Lin | Subway Train-Related Fatalities in New York City: Accident versus Suicide[END_REF] found that most of the subway-related accident and suicide fatalities concerned minorities (71% of "non-white race"). In contrast, [START_REF] Martin | Suicide patterns on the London Underground railway system, 2000-2010[END_REF] observed more white North European victims (80%) in suicide cases on the London underground between 2000 and 2010.

Characteristics of risky behaviours in relation to incidents and accidents

Based on the declared frequency of several risky behaviours by passengers in the Shanghai subway network, [START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF] distinguished between three main categories of risky behaviours in relation to accidents: transgressions (transgression of subway riding rules, violations and errors), self-willed inattention (more frequent but less risky behaviours implemented for convenience, comfort, etc.) and abrupt violations (deviation from normal behaviour). They reported that transgressions and abrupt violations were significant predictors of incident and accident involvement.

There is a partial consensus among authors on the most specific risky behaviours.

Estimating the incidence and the potential severity of the consequences associated with 19 pre-identified behaviours occurring at the PT²I, [START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF] highlighted four specific behaviours as being more risky than others: boarding or alighting when the door-close alarm sounded, squeezing into the train before alighting had finished, forcing the doors to board or alight, and finally crossing the yellow line when waiting on the platform. Likewise, Zhang et al. (2012) characterized "stepping on the yellow line" and "pushy riding" as the twin behavioural indicators of risk in the only published study based on the observation of real passengers' behaviours (although carried out at a single station). [START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF] added the use of smartphones as another frequent risky behaviour, although direct evidence was lacking. Existing indirect evidence is provided by [START_REF] Kim | Accident risk associated with smartphone addiction: A study on university students in Korea[END_REF] showing that students who are smartphone addicts have overall more accidents (of different types) than other students do, although they do not exhibit statistically more accidents in the subway (they studied the accident of being trapped in the subway). However, the lack of a significant difference could be due to the low levels of prevalence of this kind of accident (1.8% for smartphone-addicted students vs. 0.78% for non-addicted students).

Factors explaining risky behaviours

The existing literature on subway accidents focuses mostly on individual explanatory factors of risky behaviour at the PT 2 I. Zhang et al. (2012) argued that the emergence of risky behaviours could be explained by the lack of knowledge or understanding of the dangers related to the subway environment. Other authors suggested that risky behaviours could relate to the false perception of how risky the behaviour actually is [START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF]. The latter idea is debated, however. For example [START_REF] Santoso | How Safe is the Rail Platform? A Study of Bangkok Mass Transit System (BTS)[END_REF] showed that users are well aware of the safety concerns associated with some behaviours such as teasing or playing on the platform. In general, users correctly consider the platform zone and especially the space near the platform edge as risky.

Rather than implicating the cognitive level, [START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF] proposed that passengers' risky behaviour may be better explained by social norms and beliefs. Grounded on the extended theory of planned behaviour (TPB; Ajzen 2002), they surveyed a sample of habitual subway users on three specific behaviours: last-second riding, pushy riding (boarding before alighting ends) and door forcing. They found an effect of the different beliefs on the prediction of an intention to ride dangerously. Behavioural and control beliefs are consistently predictive across the behaviours surveyed (saving time, getting a seat and being late/in a hurry). Other factors increase the explanatory power of the model: moral norms, past behaviour, perceived risk and self-identity. TPB factors [START_REF] Ajzen | Perceived Behavioral Control, Self-Efficacy, Locus of Control, and the Theory of Planned Behavior[END_REF] on average accounted for 56% of variation in intentions to commit the three risky behaviours studied.

However, as with all the studies using TPB as theoretical framework, the focus is on intentions instead of actual behaviours and comprises self-reporting biases.

The literature also reports the impact of contextual factors. Zhang et al. (2012) identified in particular the effect of crowd density, speed and flow on the level of risk. With measurements at morning, noon and evening peak times, they observed the highest rate of late boarding and alighting in the evening (3% of the observed passengers) and the lowest in both morning and noon hours (less than 1%). They hypothesized that, in the evening, the subway is so overcrowded that no space is left to jump onto the train, and at noon, there is no need to crush in the train because there are very few passengers. In contrast, [START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF] showed that those passengers that ride the subway during peak periods declare more frequent transgressions of subway riding rules, inattentive behaviour and high risk behaviour.

They also report that the characteristics of the trip, of the riding area and the increase in the number of stops, predict the involvement in incidents, although no clear interpretation can be provided. Finally, Zhang et al. (2012) explained the near to zero rate of stepping on the yellow line (on the edge of the platform) observed in their study by the presence of subway staff who stop passengers effectively and in a timely manner. The difference in the results of these two studies (Zhang et al. 2012;[START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF]) may be due to a difference in the methodologies used. Zhang et al. (2012) observed passengers' behaviour at a single station of the Beijing subway, whereas [START_REF] Wan | Metro passenger behaviors and their relations to metro incident involvement[END_REF] used self-report questionnaires published on the homepage of some popular forums. Self-report questionnaires may be biased by social representations, while observations are limited to a single location and can also be biased due to physical constraints in the station environment.

Preventive measures against PT²I incidents

Within our selected set of studies, several preventive measures are adapted against PT²I incidents and their consequences for victims. In a study on the prevention of trespassrelated railway accidents and suicide, [START_REF] Havârneanu | Optimizing suicide and trespass prevention on railways: a problem-solving model from the RESTRAIL project[END_REF] distinguished between three families of preventive measures based on their nature and the mechanisms underlying their effect: technological and physical measures, organizational measures, and finally educational and communicational measures.

Technological and physical measures

Technological and physical measures refer to technical means and physical barriers to avoid the occurrence of an accident or to reduce its gravity. These measures can be implemented on the station environment (e.g. CCTV, PSD, etc.) as well as on the tracks (e.g. suicide pits, fall detector systems, etc.) or on the train (e.g. airbag, protective skirt, etc.).

Eleven distinct technological and physical measures are mentioned in 23 of our papers (Tables 3 and7).

Measures to reduce the occurrence of incidents (PSDs, sliding steps)

The Platform Screen Door (PSD) is the most widely documented measure in our corpus, and references to this measure have recently increased even further. Already in 1984,

To clear platforms faster, Baee et al. ( 2012) simulated several scenarios. When the entrance to and exit out of wagons were isolated through a separator (Boarding/Alighting Space Division; BASD), simulations showed fewer passenger collisions with a lower failure rate in boarding/alighting. The train stopping time at the platform was shorter with the BASD scenario than with the other three scenarios (Table 7).

Platform design can also change passengers' habits to reduce congestion in subway stations. Matthew ( 2005) described environmental persuasion with artwork on the walls and screens to increase social interaction and users' attention. These environments did not avoid PT²I incidents but they may create positive behaviours.

Measures to increase safety in stations (CCTV, alarms, lighting, infrared beams)

Some incidents at the PT²I are caused by malicious and illegal action [START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF]. Closed circuit television (CCTV) will not necessarily stop intrusions or accidents at the PT²I but it could play a critical role in apprehending miscreants and reducing vandalism and antisocial behavior [START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF][START_REF] Kyriakidis | A global safety analysis and best practice for metro railways[END_REF]. With CCTV, staff can detect falls or jumping onto the tracks [START_REF] Clarke | Preventing suicide on the London underground[END_REF][START_REF] Yeo | A study on the prevention of accidents in subway station through the surveys on accidents in a subway station[END_REF]). The passengers' perceptions that they are being watched may reduce crime and suicides [START_REF] Clarke | Preventing suicide on the London underground[END_REF]. In addition, the cost of installation is relatively low [START_REF] Yeo | A study on the prevention of accidents in subway station through the surveys on accidents in a subway station[END_REF]). The quality of lighting in the station could also increase safety, [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF] mentioned adequate lighting to improve safety outcomes. However, lighting has never been tested as an preventive measure in its own right in subway systems.

With the same objective, O'Donnell and Farmer (1992) presented infra-red beams as a preventive measure to avoid intrusions. They alerted the station staff if an unauthorized person attempts to enter the tunnel in Prague. The infra-red beams are rarely mentioned and do not appear to be evaluated in the literature.

Educational and communication measures

Educational and communication measures correspond mainly to primary prevention (OMS 1948). The objective is to use communication or educational programs in order to change behaviours and/or to increase attention, as well as to avoid a copycat effect related to suicide media reports. There are 5 specific educational and communicational measures distributed across 22 papers in our corpus (Table 3 and8).

Measures of public awareness (educational and communication campaign, media guidelines)

To strengthen global safety in the subway context, poster campaigns are launched to reduce risky behaviours by passengers [START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF][START_REF] Kyriakidis | A global safety analysis and best practice for metro railways[END_REF]. Public messages and information similar to what is provided for road traffic (e.g. drunk driving) could be effective in raising public awareness of risk in the subway [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]).

Communication about suicides in the subway is managed in various ways. Publicity campaigns may be counterproductive in suicide cases [START_REF] Clarke | Preventing suicide on the London underground[END_REF]. It is necessary to monitor the media very carefully. To avoid imitative effects after a subway suicide, guidelines are proposed to newspapers [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]Sonnecks et al. 1994).

The emotion induced by a communicational campaign is also important to change passengers' perceptions of risk. [START_REF] Duarte | The effect of humoristic vs. dramatic animationbased warnings: A study on acceptance and risk perception[END_REF] examined the effect of two different approaches, dramatic vs. humoristic animation-based warnings, for conveying the consequences of non-compliance. The authors showed that a video spot with a dramatic ending improved attention and risk perception, while willingness to comply was higher for the humoristic version as compared to the dramatic version (Table 8). As this study only took place on students, it seems questionable to generalize these results to all subway users. The willingness to comply is higher with the humoristic finale than with the dramatic one.

To prevent a PT²I incident before it occurs, an educational program can be used.

Educational campaigns should teach subway users about risky behaviors [START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF], they could teach commuters to leave enough commuting time and stress the hazardous outcomes related to risky riding behaviors, especially those highlighted ones. To prevent suicide, programs may specifically affect suicide rates [START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF][START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF][START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF]. In subway context, educational campaigns were not evaluated in the literature. With regard to the presentation made in the literature, campaign content should be adapted to targeted incidents and behaviours [START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF][START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF][START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF][START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF])

Staff training measures

In addition to public campaigns and educational programs, specific employee education about risky behaviours and subway suicides may also reduce subway incidents [START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF][START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF]. Guidelines to staff and police exist on how to approach a suspect or passenger in the subway in order to avoid incidents [START_REF] Gaylord | Suicide in the Hong Kong subway[END_REF][START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]. For example, the Mass Transit Railway (MTR) district in China suggested guidelines to prevent suicides [START_REF] Gaylord | Suicide in the Hong Kong subway[END_REF] including : surprise approach, direct approach, indirect approach. The effectiveness of different approaches to transit policing are difficult to assess due to limited available data [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF].

Organizational measures

Organizational measures refer to measures that aim to analyse and identify the precursors and risks of accidents. Policies and relations with the media are in this category of measures, as well as procedures to avoid or to manage an accident or risky situation. We found 4 specific measures cited in 11 articles (Table 3 and9).

Measures aiming to change passengers' habits (preferential tariff)

Passenger flow and congestion could be managed before the passengers arrive at the platform. [START_REF] Yang | Temporary Incentives Change Daily Routines: Evidence from a Field Experiment on Singapore's Subways[END_REF] proposed the use of promotional fares in order to change passengers' habits, with the idea of reducing platform congestion, conflicts and thus potential accidents. They tested a promotional fare period in the Singapore subway during 10 weeks. Before the promotion (during 20 weeks), only 5-10% of morning trips ended before 8:00, against 15% for the early treatment (ET) and late treatment (LT) groups during the promotional period. The post promotion (during 30 weeks) percentages for ET and LT were consistently higher than that of the control group (Table 9).

Measures to increase station safety (presence of surveillance units) [START_REF] Niederkrotenthaler | Predictors of Suicide and Suicide Attempt in Subway Stations: A Population-based Ecological Study[END_REF] showed that the presence of surveillance units in Vienna subway stations reduced the number of suicide attempts (Table 9). Station agents maintain order, and passengers engage in less risky behaviours when they are present in the station. They help to discipline passenger behaviour and prevent risky ridings [START_REF] Wan | What factors determine metro passengers' risky riding behavior? An approach based on an extended theory of planned behavior[END_REF]. [START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF] considered that it is necessary to increase surveillance by station staff since increasing the visibility of police is an important component in reducing the overall climate conducive to violent crime [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]) and suicides [START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF].

However, the effect of the presence of surveillance units on the number of suicide attempts could be due to others variables (e.g. crowdedness of stations) but a more frequent assessment was not possible due to the lack of data [START_REF] Niederkrotenthaler | Predictors of Suicide and Suicide Attempt in Subway Stations: A Population-based Ecological Study[END_REF].

Measures to adapt the speed limit of trains

Another suggestion to reduce injuries after PT²I incidents without engineering is to change the speed limit of trains entering a station [START_REF] Mishara | Suicide in the Montreal Subway System: Characteristics of the Victims, Antecedents, and Implications for Prevention[END_REF][START_REF] Mishara | Railway and Metro Suicides: Understanding the Problem and Prevention Potential[END_REF]. In 1984, Johnston and Waddell proposed an entrance speed of 10 miles per hour instead of 45 mph after analysis of death and injury patterns in the Toronto subway. Several years after this publication, [START_REF] Guth | Public Health Lessons Learned From Analysis of New York City Subway Injuries[END_REF] also proposed to reduce the speed at which trains enter the station, which could decrease the severity and lethality of injury and allow the driver more time to notice a person on the tracks. However, for authors at 10 miles per hours, it would take a considerable distance to train to stop and the severity of the body still be considerable [START_REF] Johnston | Death and Injury Patterns, Toronto Subway System 1954-1980[END_REF]. However, reducing speed means reducing the frequency of trains, which affects the available transport supply and increases congestion; this congestion can lead to an increase in the risk of accidents. Although a reduced entry speed in station is necessary, too much speed reduction may not be an appropriate solution to avoid PT²I incidents. Further studies are needed to anticipate the beneficial and negative consequences of a possible reduction in the speed of trains entering a station

Measures using incidents feedback (MOID, STAMP, RAIB)

Zhou and Yan (2018) compared the analysis results of RAIB with that of STAMP of one accident (the passenger trapped in train doors and dragged at station) on the London underground ( RAIB investigations help to identify the events that have led to an accident, but do not identify the relationship between these events and the cause(s) of the accidents. This RAIB investigation could be used as an information source. STAMP analyses the relationship between various causal factors and causes. It provides the examine the entire sociotechnical system design to identify the weaknesses in the existing safety control structure [START_REF] Leveson | Engineering a safer world: Systems thinking applied to safety[END_REF]. STAMP provides a more comprehensive perspective than RAIB investigation to ensure the safety of a system.

With the same objective of improving safety by using feedback, [START_REF] Zhang | An incident database for improving metro safety: The case of shanghai[END_REF] created a database called: Metro Operation Incident Database (MOID). It brings together three types of incidents in the Shanghai subway: serious accidents, non-serious accidents and near misses (Table 9). With MOID in the Shanghai subway, 24 accident precursors were identified. The authors concluded that MOID analysis could help the subway company and the government to manage and improve operation safety.

Conclusion and perspectives

The subway is a risky environment, especially at the interface between the platform, train and tracks (PT²I). Some results emerge from the literature. Accidents occur more during rush hour or very off-peak hours, such as at night. In other words, accidents occur when the metro network is overcrowded or almost deserted. Moreover, accidents seem to occur more during the boarding and alighting of passengers. The people involved in accidents are predominantly middle-aged men, in an altered state of consciousness (alcohol and drugs detected). In the majority of cases, accidents are considered to be directly related to user risktaking behavior, whether due to a lack of knowledge or deliberate flouting of the regulations, either to maximize personal comfort or out of a desire to transgress.

Our review has shown that this subject has been insufficiently studied and that existing studies do not allow us to conclude on the factors involved in the occurrence of accidents and the efficient associated preventive measures. Various phenomena make it difficult to cross-reference the existing literature on the subject. First, there is no international consensus: the categories of incidents and their definitions vary from one country to another.

Second, most existing studies consider both accidental events and suicides. Third, studies focusing on user behaviour and risk perception are very sparse; by the way, they are mostly located in Asia. Fourth, each network studied has its own characteristics, both physical and in terms of passenger flows, which makes it difficult to make reliable comparisons. Finally, too few studies validate the effectiveness of preventive measures, which are most often only mentioned in passing. In addition, some of these evaluations or propositions are dated, changes have occurred in the subway environment that have rendered certain measures obsolete (e.g. speed limit, airbag on train, etc.). The majority of studies do not mention the potential impact of the proposed or evaluated measures on the subway operation (e.g. frequency reduction, structural adaptations, etc.).

To address these weaknesses, we argue that more research is needed and that it is necessary to draw on what is proposed in systemic approaches, i.e. to look at the problem as a result of the interaction of all the system's components, considering the whole as the unit of analysis, not just individual's behaviour. Indeed, several levels of explanatory factors could be involved in incident and accident development from a system-oriented approach [START_REF] Hollnagel | Barriers and accident prevention[END_REF]Leveson 2011b;[START_REF] Read | Associations between task, training and social environmental factors and error types involved in rail incidents and accidents[END_REF][START_REF] Stefanova | Systems-based approach to investigate unsafe pedestrian behaviour at level crossings[END_REF][START_REF] Wilson | Fundamentals of systems ergonomics/human factors[END_REF]. For example, [START_REF] Stefanova | Systems-based approach to investigate unsafe pedestrian behaviour at level crossings[END_REF] analysed in particular the following levels: individual, sociocultural environment, the equipment and surroundings, and lastly the organisational level.

The organisational level includes all the factors related to the management of the systems (e.g. urban planning, station design, procedures and policy, human resources, collaboration between organisations, public safety awareness campaigns, etc.). The equipment and surroundings level encompasses contributing factors related to the characteristics of the environment (e.g. type of tracks, presence of controls, etc.), the size of the urban area, the temporal characteristics of the moment (e.g. time of day, weather). The social environment refers to the visible presence of other actors (including both other passengers -our case -, staff, police patrols, etc.) in the immediate context and the way they behave. Finally, the individual level includes various dimensions strictly related to the characteristics of the persons. While the few existing research explores almost exclusively the later level, very few theoretical considerations have been adduced to explain behaviours (only the attitudes are considered). Furthermore, the prevention of unsafe passenger behaviour and the apprehension of associated risk factors require taking intentionality into account, i.e. distinguishing between errors and violations [START_REF] Stefanova | Systems-based approach to investigate unsafe pedestrian behaviour at level crossings[END_REF][START_REF] Reason | Errors and violations on the roads: a real distinction?[END_REF]). While errors result from failures on different levels of information processing (skill, rules, knowledge-based levels of performance) and are thus associated with cognitive precursors, violations highlight the role of social context in decision-making (e.g. social norms, rules, operating procedures)

and are therefore associated with motivational factors which lead the person to intentionally deviate from the prescribed rules [START_REF] Reason | Errors and violations on the roads: a real distinction?[END_REF]). This distinction will inevitably have an impact on the modes of prevention to be considered. Errors are more likely to be minimised through "retraining, redesign of the human-machine interface, memory aids, and better information", whereas violations are more likely to be reduced by the modification of attitudes, norms, beliefs or the overall safety culture [START_REF] Parker | Driving errors, driving violations and accident involvement[END_REF](Parker et al. , p.1036)).

Existing technological, physical, educational and organisational preventive measures act at different levels of prevention (primary, secondary or tertiary). Concerning technological measures, PSD, suicide pits, CCTV, detection with infrared beams and the appropriate (re)design of the front train material are solutions that were identified long ago.

Sliding steps, alarms, lighting, and barriers associated with a good ticketing system appeared more recently. Educational and communicational measures include educational and communication campaigns, media guidelines to avoid copycat behaviour, and staff training.

A wide range of organisational measures have been identified: trying to change passengers' habits by using ticketing policies or by the presence of surveillance units, adapting the train speed to facilitate the mitigation of critical situations, and fostering organisational learning by using incidents feedback. Most of the identified measures have not yet been evaluated however. In fact, the available evidence is meagre, and concerns a very small set of measures such as Platform Screen Doors, or Suicide pits. Other preventive measures used in the railway context could be relevant for subway networks. In their review, [START_REF] Havârneanu | A systematic review of the literature on safety measures to prevent railway suicides and trespassing accidents[END_REF] showed the effectiveness of communication and educational programs, and reinforcement to avoid trespassing. PSDs are sufficiently well documented to stand out as the most effective measure in terms of accident prevention and mitigation of feelings of insecurity. Unfortunately, this installation is very expensive, especially for already built subways [START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF]. We found in our literature review other, less costly preventive measures such as reducing the speed limit. One opportunity to decrease the accident rate is to change users' behaviour using implicit techniques (station design, promotional tariffs) or targeted communication programs.

Subsequently, suggestions for future research and for public authorities include the study of the actual behaviour of subway users through systematic observations taking into account its various determinants within a system-oriented framework. At the moment, we have too little information on the characteristics of a situation that may lead users to adopt or not certain behaviours. This information would make it possible to propose preventive measures acting on the precursors of behaviours. Research should also screen the effectiveness of different preventive methods depending on where they are implemented and the specificities of the place. The physical and socio-economic environment of the station must be taken into account. Some measures can only be effective in specific contexts and cannot be extended to all stations. The evaluation of preventive measures requires more information about passengers' habits and perceptions. Preventive measures do not have the same effect depending on the habits and experience of users and this must be measured and this consideration of passengers' perceptions would improve the acceptability of certain measures and improve their effectiveness.This information could make it possible to propose new, cheaper interventions to reduce risky behaviours or to increase passengers' knowledge.

Finally, international standards in the definition of accidents and their categorisation would significantly improve future research, together with the development of databases for systematically recording detailed information about the conditions of the accident and the characteristics of the victim. Indeed this would provide a strong support for the comparisons and monitoring of accidents at both national and international levels, as well as a useful framework for the development of research on precursors and prevention of individual accidents in subway systems.

Fig. 1

 1 Fig. 1 PRISMA flow chart Studies were identified by searching through several scientific databases covering peer-reviewed journal papers published in French and English up to January 2019 in behavioural science, social science and medicine (Scopus, PsychINFO, and Google Scholar).

  Vienna subway Source: Records of Austrian daily newspapers Period: 1984-1987 Results: Weekday with the most suicides was Monday. Location: Shanghai subway Source: Data collected in literature and media Period: Jan. 2005

Table 2

 2 Distribution of references by main topic and design

	Time	Main topic	Design	Tot.

Table 3

 3 Distribution of preventive measures in the corpus (() number of evaluations included)

	Type of measures

Table 4

 4 Summary of the studies that provide empirical results about subway incidents with different causes R November and December had the highest suicide rates.Midday is the time when most suicide attempts were made.

	eference	Data description and main results	Sample
	( 3 authors, date)
	S tudies using fatality records
	G ershon et al.	Location: New York city subway	315 fatal accidents: 91% male, 35-44 years, 46% with
	( 7 2008)	Source: Review of medical files at the Office	alcohol, 31% with drugs, 71 % of non-white victims
		of the Chief Medical Examiner of NYC	343 suicides: 78% male, 25-34 years, 18% with
		(OCME)	alcohol, 21% with drugs, 62% of non-white victims
		Period: 1990-2003	10 homicides: 60% male, 35-44 years, 0% with
			alcohol, 60% with drugs, 90% of non-white victims
	1 H e et al. (2015) Location: Shanghai subway	3 fatal accidents,
		Source: Review of unnatural deaths at the	2 suicides,
		Shanghai Public Security Bureau	1 undetermined death
		Period: 2000-2009

Results: All decedents were males with an average age of 36 years 2 L in and Gill 2 ( 2 2009) Location: New York city subway Source: Death certificates of OCME with the words "subway", "train" or "tracks" Period: Jan. 1, 2003-May 31, 2007 76 fatal accidents: 86% male, mean age 44, 42% with alcohol, 25% with drugs, 8% with antidepressant medication 111 suicides: 81% male, mean age 45, 14% with alcohol, 3% with drugs, 21% with antidepressant medication 20 undetermined deaths 4 homicides Results: 2% of deaths are caused by electrocution and the others by blunt force.

Greatest number of suicide deaths occurred in May and on Tuesday.

Accidental deaths occurred most in March and December with low day-to-day variability.

3 M ishara (1999) Location: Montreal subway

Table 5

 5 Summary of the studies that provide empirical results about subway incidents and patients after subway-related incidents.

	50Reference	Data description and main results	Sample
	(authors, date)
	Studies using incident records
	54Coats &	Location: London underground	58 incidents
	Walter (1999)	Source: Records of incidents	% deaths: 57
		Period: Jan. 1996-March 1997
	O'Donnell,	Location: London underground	3240 incidents
	& Farmer	Source: Records of railway operations and passenger services	% deaths: 10

Results: 45.5% of patients were unemployed, 25% of cases were suicide attempts, Similar pattern between unemployment rates, homeless rates and subway injuries.

Table 6

 6 Summary of the studies that provide empirical results about subway suicides Suicide deaths occurred most in May and June and the majority of victims (80%) were white North

	7Reference	Data description and main results	Sample
	(authors,
	date)
	11Studies using fatality records
	Martin	Location: London underground	132 suicides
	and	Source: British Transport Police	% male : 66
	Rawala (2017)	Period: 2004-2010	Mean age : 43
		Results: European
	Study using incident records
	Ladwig	Location: Munich subway	306 suicide attempts
	24(2004)	Source: MVG case registry	% deaths: 66
		Period: 1980-1999	% male: 53
			Mean age: 38

Table 7

 7 Summary of the studies that provide evaluation of technical and physical measures Reference Door placed at the center of the arrival platform, to traverse the platform uniquely from South to North, 3 removable unidirectional doors on weekdays between 7 and 9 a.m.

		Study design and measures	Significant results reported
	(authors,
	21date)
	Platform screen doors
	Chung et al.	Location: Seoul Metro	Suicides in subway stations
	25(2016)	Intervention: Half-height PSDs (1.65m) at two stations and full-	decreased significantly after
		height PSDs on 119 stations	installation of PSDs (-89%)
		Study design: Quasi-experimental, ecological study with before
		and after measurements, based on the number of suicides
		Data: 135 suicides on 121 stations
		Period : 2003 to 2012
	Law and Yip	Location: Hong Kong railway system	Installation of PSDs reduced
	(2011)	Intervention: PSDs in 30 stations in 2002	casualties (-67.5% suicidal; -
		Study design: Quasi-experimental, ecological study with before	69.5 accidental)
		and after measurements, based on injury data
		Data: 402 casualties (154 suicidal, 248 accidental)
		Period: 1997 to 2007
	Portillo-	Location: Zocalo subway station (Mexico City)	84% of subway passengers who
	43Villasana et	Intervention: PSDs	have the intention to commit
	al. (2017)	Study design: Simulation software ("AnyLogic"), Analysis of the	suicide succeed without PSDs
		effectiveness of physical barriers with two scenarios (with or	against 24% with PSDs
		without PSDs)
		Data: 100 simulations
	Santoso et al.	Location: Bangkok subway	Installation of PSDs was
	(2013)	Intervention : PSDs	perceived positively (76.67%
		Study design: Questionnaire survey about platform safety by users	agree) provided it does not
		(21 items), four items on the perception of PSD installations	imply any increase in the fare
		Data: 120 valid questionnaires (65% female, 54.17% aged 26-60
		years)
		Period: Nov. 2012
	Doors on the platform

Data: Nine stations (start station: all in flow; end station: all out flow; six regular stations and one inter-change station)

Table 8

 8 Summary of study that provides evaluation of communicational measures

	Reference	Study design and measures	Significant results reported
	(authors, date)
	Video-spot
	Duarte et al.	Intervention: Dramatic finale versus humoristic finale of	Attention capture, understandability,
	(2014)	animation-based warnings to convey the consequences of	explicitness are statistically higher
		non-compliance	with dramatic finale than with
		Study design: Experimental, comparing questionnaires	humoristic one.
		(attention, understandability, compliance, explicitness,
		risky behavior, hazard injury, injury likelihood, injury
		severity, drama, humor, duration),
		participants randomly assigned to dramatic or humoristic
		finale
		Data: 60 students (Mage = 22.6): 30 in each group
		Period: not specified

Table 9

 9 Summary of the studies that provide evaluation of organizational measures

	Reference (authors, date)	Study design and measures	Significant results reported
	Presence of surveillance units

  Table9). The rail accident investigation branch (RAIB) is a British government agency, created in 2005, that investigates fatal accidents causing death in the UK main line networks, the London underground and other subway systems, and tramways. RAIB investigation aims to increase railway safety by preventing future railway accidents or by mitigating their consequences. STAMP is an accident causation model. It analyses each component and controller of the system according to the safety control structure. With the result of RAIB investigations and STAMP analysis of the same incident, the authors concluded that the analysis and the explanations are more objective with RAIB investigation.

Acknowledgements 295(6612):1527-1529. https://doi.org/10.1136/bmj.295.6612.1527

Johnston and Waddell proposed this measure to prevent accidental or deliberate injuries involving moving subway trains. PSDs are physical barriers that limit passengers' access to the tracks by separating the rail from the platform [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]. They can be full or half-height. PSDs open only when the train stops at the station [START_REF] Chung | The effectiveness of platform screen doors for the prevention of subway suicides in South Korea[END_REF][START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]. PSDs have already been installed in several subway networks around the world (Clarks and Poyner 1994;[START_REF] Kyriakidis | A global safety analysis and best practice for metro railways[END_REF]. Their primary objective is to reduce falls, trespassing and suicides [START_REF] Chung | The effectiveness of platform screen doors for the prevention of subway suicides in South Korea[END_REF][START_REF] Kyriakidis | Metro railway safety: An analysis of accident precursors[END_REF]. Several studies have evaluated this measure and have confirmed its effectiveness (Table 7). PSDs reduce suicide attempts by around -80% on average [START_REF] Chung | The effectiveness of platform screen doors for the prevention of subway suicides in South Korea[END_REF][START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF]Yip 2011, Portillo-Villasana et al. 2017) and accidents by -69.5% [START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF], thereby contributing to reducing the time of service disruption by 64% [START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF]. These studies do not distinguish the use of full-height and half-height PSDs. The height of the doors can have an impact on the effectiveness of this measure. However, new risks have emerged with PSDs, passengers could be unfortunately restrained and killed in the gaps between PSDs and the doors of the train. To reduce these risks, [START_REF] Zhang | Monitoring the gaps between the platform screen doors and the doors of subway train based on optical time domain reflectometer[END_REF] propose to install a sensor system to monitor passengers and intrusion at the gaps based on optical time domain reflectrometer (OTDR). The presence of intrusions will be detected if the abrupt power loss at the locations of gaps is over a predetermined value. In their study, authors did not propose any data on the effectiveness of this system.

PSDs may also increase the perception of safety on the platform. In the Bangkok subway, passengers perceived this measure positively (mean of ⅘) provided that it did not imply any increase in the fare [START_REF] Santoso | How Safe is the Rail Platform? A Study of Bangkok Mass Transit System (BTS)[END_REF]). However, the installation of PSDs represents a huge cost of several million dollars for operators (Chung et al. 2008;[START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF]. [START_REF] Law | An economic evaluation of setting up physical barriers in railway stations for preventing railway injury: evidence from Hong Kong[END_REF] examined the effectiveness and cost-effectiveness of PSDs in preventing injuries in the mass transit railway of Hong Kong with the "WHO-CHOICE" method (Table 7). With their approach, PSDs become cost-effective when the expected useful life is extended by two additional years to 27 years. Furthermore, this analysis did not include the cost saving of energy conservation.

Another system can reduce the occurrence of PT²I incidents. The gaps between platforms and trains could also provoque incidents. This gap may be due to station design (curved area) or train characteristics. Sliding steps exist either on platforms or trains (Table 3). They fill the gap between the train and the platform. If the sliding step is installed on the vehicle, it is possible to respond to the various platform typed. This system has been validated as safe to use on subways but is not systematically used in existing networks [START_REF] Joung | A study on system to reduce the gap between subway vehicle and platform[END_REF].

Measures reducing the consequences of incidents (suicide pit, front train material)

The first mention of a suicide pit was in 1936 in the London underground [START_REF] Cocks | Study of 100 patients injured by London underground trains 1981-6[END_REF]. A suicide pit is a drainage pit under the tracks, usually about a meter deep [START_REF] Coats | Effect of station design on death in the London Underground: observational study[END_REF]. These pits increase the clearance between the train and the ground. As a result, after falling, an individual can lie safely underneath the train [START_REF] Gershon | Epidemiology of subway-related fatalities in New York City, 1990-2003[END_REF]. Studies found that suicide pits did not reduce the number of incidents but the mortality rate decreased (Coats and Walters 1999;[START_REF] O'donnell | Suicidal acts on metro systems: an international perspective[END_REF]. In the London underground, the fatality rate was on average 70% without pits and 45% at stations equipped with pits (Table 7) (Coats and Walters 1999;O'Donnell andFarmer 1992, 1994). Nevertheless, references to suicide pits as a preventive measure have declined since 2007.

In the nineties, [START_REF] Clarke | Preventing suicide on the London underground[END_REF] proposed other mechanisms on the front of the train to reduce injury such as an air bag or protective skirt. These mechanisms are not effective at high speeds but could avoid some fatalities in stations [START_REF] Clarke | Preventing suicide on the London underground[END_REF].

However, these systems have not been tested and changes in train design may make such additional devices unnecessary.

Measures avoiding passenger congestion (gates on the platform, platform design)

Passenger flow and congestion can be precursors of accidents. In the Santiago subway, unidirectional gates were installed in the middle of the arrival platform to constrain passenger flow on the platform to the South to North direction. The objective was to avoid counterflow on the platform. This installation decreased the platform's clearing time, generating a higher transport capacity -trains were more frequent and more reliable -and a higher level of safety as it eliminated passenger counterflow (Table 7). A few days after installation, users approved this initiative (Munoz et al. 2018). This installation has been preceded by public relations campaign and campaign reinforcement to requesting changes in boarding behaviour.

Two policemen stood next to the gate during the first two weeks of the installation to ensure its proper operation but subway personnel still stated the passenger counter-flow once a day (Munoz et al. 2018). Authors do not indicate the duration of the experiment; the effects of this intervention could change over time.

This study has been conducted as part of the project "Sécurité à l'IQTV" which was coordinated by the STRMTG. The authors would like to thank all collaborators for their support during the development of this work.