PERSIAN traffic safety and health cohort: a population-based precrash cohort study


Road traffic injuries (RTIs) are one of the major health concerns and causes of mortality especially in low and middle-income countries (LMICs).1 2 Developed countries with high motorisation have the lowest rate of road traffic crashes (RTCs) with less than 50 per 1000 people.3 RTIs account for 41.2 million years of healthy life lost, and 90% of disability-adjusted life years in LMICs.4 5 The global average deaths from RTCs as part of intentional and unintentional injures are about 24%, however, in Iran, it is more than 50%. According to the 2018 Global Status Report on Road Safety, the estimated rate of road traffic deaths in Iran was 20.5 per 100 0000 people. Also, the number of deaths by RTCs in the world is three people for every ten thousand cars, while it is 33 people for every ten thousand vehicles in Iran.6 RTIs are the eighth leading cause of death worldwide, but in Iran, they are the second leading cause of death and are accounted for 80 000 major traumas yearly.7 8 RTCs and RTIs cause serious economic loss approximately 1%–2% of Gross National Product in high-income countries and 6%–7% in Iran.9 Furthermore, it is estimated that RTIs would cost the world economy US$1.8 trillion from 2015 to 2030.10

According to the definition of European Union and the International Transport, an RTCs is any accident involving at least one road vehicle in motion on a public road or private road to which the public has right of access, resulting in at least one injured or killed person.11 The risk factors related to RTCs are classified into three main factors, including human factors, road-related factors and vehicle-related factors. Human factors are the most common risk factors involved in RTCs.12 13

Although numerous studies have been conducted in the field of RTIs, there is no significant progress and it still remains one of the most serious public health problems in Iran.14–16 Therefore, one of the main priorities of the government is to obtain substantial evidence to improve traffic safety, reduce the burden of injuries and their various consequences. For this purpose, a comprehensive scientific study is required to assess the relationship between human factors and violation of traffic law, injury, the severity of the injury, hospitalised injury and deaths using Haddon’s matrix approach.17

Prospective population-based cohort studies are a fundamental design in epidemiological studies. They cover a wide range of research questions and assess the association among various variables individually, and in combination.18

Thus, to get a more robust inference about the causality of RTCs, the PERSIAN Traffic Safety and Health Cohort (PTSHC) study was established in 2019, in Iran. The PTSHC has two separate parts; the population-based cohort for precrash and the registered-based cohort for postcrash. The postcrash cohort data are presented in a related article.19 Other than human-related assessments which are robustly evaluated, precrash PTSHC also measures and controls for the effects of vehicle safety, vehicle use and land-use in traffic injury causality network. Furthermore, considering that this cohort is a household based, it provides an opportunity to examine the status of family aggregation in various traffic issues, including high-risk behaviour.

In order to respond to this major public health problem, the prospective precrash cohort study was designed for 30 years and is financially supported nationally and locally. This study has national funding from Ministry of Health and Medical Education and local funding from the Tabriz University of Medical Sciences. Moreover, this cohort study is systematically supported by the RTI Research Center (RTIRC) a centre of excellence specialised research centre on RTI prevention. Regarding this, study is the first priority of the RTIRC, the research centre has invested significantly in the field of human resources and equipment.

Cohort description

The precrash cohort study is a population-based prospective study that is part of the PERSIAN cohort and is carried out in four cities of Tabriz, Jolfa, Shabestar and Osku in East Azerbaijan province located in northwest Iran (1 600 000 residents).

This cohort study is systematically supported by the RTIRC (hereinafter referred to as the Centre), TBZMED. The Centre has a key intersectoral national role in RTIS prevention and road safety promotion as well as good capacity and experience at regional and international levels. This Centre is equipped with a Health and Traffic Safety Clinic and a laboratory to examine physical/mental health and driving behavioural performance.

Study participants and data collection

The participants in the prospective precrash cohort study were people who were sampled among the general population. The cluster sampling method was used to determine the households in this study. At first, the source population was categorised into three strata in term of socioeconomic status according to the place of residence. Then 25 clusters were chosen from within the strata. Next, 20 households from each cluster were selected to participate in a study using convenience sampling. The estimated sample size is 10 000 households. Until now, a number of 7200 subjects have been included. Also, approximately 1 220 000 person measurements have been collected. The sample size of this study will be grown up over time due to the openness of the cohort.

Trained interviewers do data collection. The interviewers go door to door with the determined households to explain the study objectives face-to-face and obtain their informed consent. The face-to-face method is an effective method to improve the participation of Iranian families into the study. If the individuals agree to participate, recruitment and enrolment occur and the general background information about the household is completed. The reasons for participation refusal are recorded if declared.

After that, the other questionnaires are given to the representative of each family and it is requested that all people over 14 years of age in the family complete them. Then, the completed questionnaires receive by coordinating and referring again. After that, all participants are contacted by phone and invited to attend RTIRC. Next, the specified measurements in the Traffic and Health Clinic, and Traffic Health and Behavioral Laboratory are performed. Later, the subsamples of participants are invited for selected specialty assessments such as Vienna Test System (VTS) and Electronic Travel Behavioural Monitoring. The inclusion criteria were comprised of the provision of informed consent and enrolment at baseline. The exclusion criteria comprise having no phone number for contact and follow-up and deaths, migration during the follow-up period or refusal to participate.

Cohort online system

Because multiple stakeholders were involved in the traffic cohort project and in order to facilitate data transfer among them, we decided to use an open-source programming approach for developing databases, user interfaces and middleware. We used Structured Query Language (SQL) databases and Java platforms for the backend, HTML and JavaScript programming languages for frontend user interfaces. The whole platform was designed using Model-View-Controller architecture. That approach makes it possible for quick expansion of the cohort system if a need arises and facilitates its integration with other registry systems housed inside other organisations where they were using heterogeneous internal systems for data collection, storage and processing. Protecting data against unauthorised access was the highest priority in designing the cohort registry system.


The prospective precrash cohort is planned to follow-up with participants for at least 30 years. The outcomes of this study are incidence of the crash, injury, severity of the injury, hospitalised injury and deaths. The first follow-up in this open prospective cohort will begin after 1 year, and then follow-ups will be done every 5 years (figure 1).

Figure 1
Figure 1

Timeline of prospective precrash cohort of health and traffic safety and follow-ups.

Quality controls

To ensure that all participants are enrolled in the study according to defined protocol, as well as to decision make based on valid and reliable data, quality assurance (QA) and quality control (QC) have been implemented by central and local QA/QC teams. QC involves three types of assessments: completeness, timeliness and correctness. Completeness and timeliness refer to the percentage of completion of question in the questionnaires by the participants and data collection according to the schedule, respectively. For assessing correctness, three types of evaluations were conducted: control random check, validity check and cross-check.

Risk factors and outcomes assessment

The measurements in this study are carried out in three main parts: the measurements for the human factor, the measurements for land-use and vehicle factors. The outcomes of this study are defined by the occurrence of the crash and its related injuries. The defined exposures in this study are human factors, including physical health, mental health, clinic examination, psychiatric clinic examination and preclinical examination.

The land-use and vehicle-related factors (include of traffic laboratory tests, vehicle clinic tests and road-related tests) are measured as predictor variables. Various tools are being used from previous studies or are designed and validated through the project. Figure 2 provides an overview of the measures that are used in this cohort study. Each part of the assessment and data collection is explained as follows:

Figure 2
Figure 2

Overview of the measurements in the health and traffic safety pre-crash population-based cohort study.

Household survey

In household-level measurements, the general background information about age, sex, job, literacy and insurance situation of the family members is gathered. Moreover, the socioeconomic status of the household is assessed using the short versions of the SESIran questionnaire, which was developed and validated in Persian by Sadeghi-Bazargani et al20 Measurements are performed by trained interviewers who visit respondents at home. On average, this interview takes 40 min to complete. To obtain additional data, respondents are asked to fill out a written questionnaire separately, which is left at the respondent’s home after the visit.

In-person survey

In an in-person survey, the information is gathered in three main parts; physical health, mental health, and safety behaviour.

Physical health assessment

In physical health assessment, the main parameters are scheduled such as general health status using the standardised and validated General Health Questionnaire,21 sleep quality by Pittsburgh Sleep Quality Index,22 quality of life using a Persian version of WHO quality of life questioner (WHOQOL),23 visual screening, hearing screening. Psychometric properties of the questioners available in the published studies. Moreover, the examination of diabetes, stroke diseases and brain haemorrhage are done. After the consent of the participants, the participants are invited to an in-person visit at the study site, and a physical examination is performed by a qualified general practitioner.

Mental health assessment

The mental health status of participants is examined by a psychiatrist through a Structured Clinical Interview for DSM Disorder in terms of several disorders. The main parameters of mental health are scheduled including adult deficit/hyperactivity disorder by CONNERS’ Screening Scale, Standardized Assessment of Personality, Personality inventory for DSM-5 brief form, Psychological Distress assessment using Kessler, major depressive disorder, mood disorder, Post traumatic stress disorder, Traffic psychological assessment using VTS, anxiety disorder, adaptive disorder, alcohol or drug use, schizophrenia or psychosis disorder, personality disorder. The participants are invited to an in-person visit at the study site and after they give consent, they are offered counselling with a qualified psychiatrist.

Behavioural assessment

Assessing the traffic behaviour of a person is considered according to his/her role in the traffic environment. In behavioural assessment, the main parameters are scheduled such as traffic behaviours by Pedestrian Behavior Questionnaire, Motorcycle Riding Behavior Questionnaire, Persian version of Manchester driving behaviour, reaction time, collision avoidance behaviour, total brake reaction time, driver performance, driver distance travelled, pedestrian walking travelled, travel pattern, compliance with traffic laws and virtual driving assessment on a driving simulator.

Vehicle assessment

The measurements related to vehicles are classified into five categories:

  1. Vehicle characteristics including vehicle model, type and vehicle age.

  2. Vehicle safety specifications at the production level such as airbags, the number of airbags, Electronic Brake-force Distribution, Electronic Stability Programme, etc.

  3. Measurements related to road use and vehicle use such as vehicle kilometres travelled.

  4. Information obtained from machine data includes speed, acceleration, location, etc (machine data is digital information created by the activity of computers, mobile phones, embedded systems and other networked devices that are installed in a vehicle).

Patient and public involvement

Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

Studies and findings to date

From late 2019 up to now, 7200 people have been recruited in this study. Of them, 51.14% (3546 people) were men. The mean age of participants was 39.23 (SD=19.96) years. The majority of participants (55.41%) belong to the age group of 30–56 years. The data of this study will be published in different articles. The selected summary results of this study are shown in table 1.

Table 1

The mean score of some assessments including of Kessler, SAPAS, GHQ according to age groups and sex

One of the main goals of this cohort is to develop health and traffic knowledge. Therefore, a number of master’s and PhD theses and research projects are part of this cohort study. The details of theses and projects that have been enrolled up to this time are presented in table 2.

Table 2

The details of theses that have been enrolled in Traffic Safety and Health Cohort

This study was not only effective in determining the pattern of risk factors affecting the occurrence of accidents but also able to determine the necessary interventions in prevention and provide practical programmes and solutions to reduce the risk of accidents and traffic violations and their subsequent consequences. Also, this study produced evidence-based data that is a basis for policymaking for planners in the field of traffic accident prevention.

The studies conducted in the field of traffic are only on the accidents and no study in the current conditions has been able to measure the role of vehicles and the injuries caused by them in the occurrence of accidents, which the cohort study has fully investigated.

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