A 50-year analysis of Transport for London staff found that bus and tube staff had higher death rates than office workers, raising important questions about workplace exposures, working conditions and long-term worker health.
Study: Transport mortality among London workers. Image credit: TiberPics / Shutterstock
In a recent retrospective study published in the journal scientific reportResearchers analyzed more than 50 years of data from 1960 to 2021, from a long-term follow-up study of more than 117,000 Transport for London employees, to examine disparities in mortality rates by occupation.
The findings revealed that bus and London Underground (LU) workers had significantly higher all-cause, respiratory and cardiovascular mortality rates than office workers. Most notably, LU workers and bus workers were found to have more than twice the risk of lung cancer compared to office workers. Although these findings are consistent with possible occupational and environmental influences on long-term health in urban transportation systems, this study could not identify specific causes of the observed differences.
Government-maintained records highlight that London’s transport network is one of the busiest in the world, with estimates suggesting it facilitates around 26.1 million people’s journeys each day. The city’s intermodal transport system is operated by Transport for London (TfL), which reportedly employs an occupationally diverse workforce (n = ~30,000).
Occupational stressors and environmental exposures
Previous research suggests that transportation workers are exposed to a variety of physiological stressors (e.g., prolonged sitting) and psychological stressors (e.g., irregular shift work) on a daily basis. Researchers further hypothesize that certain occupations may expose employees to high levels of environmental pollutants.
For example, in underground tunnels, workers can expect to breathe air with high levels of particulate matter (PM) produced by train wear, while bus drivers contend with exhaust fumes and traffic noise on the road. Previous research has investigated short-term health issues associated with TfL employment, but long-term trends in transport-related occupational injuries remain unclear.
This study aimed to address this knowledge gap by assessing whether specific everyday occupational hazards are associated with differences in mortality risk among TfL workers. The study employed a retrospective cohort design using data obtained from the TfL Pension Fund. The dataset consists of 117,166 employees who joined the fund between 1960 and 2010, with tracking data extending to October 2021.
Worker categories and analytical approaches
The research analysis divided TfL workers (study participants) into four main cohorts: bus worker – A group including bus drivers, ticket sellers and bus conductors engaged in ground transportation, 2. London Underground (LU) workers – A broad category that includes everyone who works in an LU organization, such as drivers and customer service staff, but also some office workers and engineers. 3. engineer – Diverse groups involved in maintenance and technical roles, and 4. company employee – Non-work staff who held desk-based roles and served as a statistically control (“reference”) cohort.
Participant data included pension fund records and death certificate information. Statistical analyzes primarily used Cox proportional hazards models to compare hazard ratios (HRs) based on mortality across participants in the four main cohorts. The model was specifically adjusted for participants’ sociodemographic and occupational variables, particularly age, gender, employment tenure, and the decade in which the worker joined the company.
Differences in all-cause mortality between roles
Study results revealed that participants in the bus and LU categories exhibited a significantly higher risk of death than office-going participants (cohort 4). Descriptive statistics showed that 37,849 people died within the entire cohort over the 50-year period.
All-cause mortality data showed that LU and bus employees had the highest risk of death, with a 23% and 17% higher risk of death than control participants (HRLU 1.23, 95% CI 1.15 to 1.32; HRBus 1.17, 95% CI 1.09 to 1.25). Unexpectedly, engineers did not show a statistically significant difference from office workers in all-cause mortality outcomes (HREng = 0.97).
Mortality and lung cancer risk by cause
When evaluating a specific cause of death:
- Respiratory mortality – LU and bus workers were shown to have a 73% and 44% higher risk of respiratory mortality compared to office workers.
- Cardiovascular mortality – LU had a 51% increased risk, while bus workers had a 30% increased risk.
Most notably, LUs (HR = 2.85) and bus workers (HR = 2.48) were found to be more than twice as likely to die from lung cancer compared to office workers, but the study could not determine whether occupational air pollutants were directly responsible for this pattern.
Additionally, although some analyzes showed LUs to have the highest risk rates, the mortality rates for LUs and bus workers were found to be statistically similar, leading the researchers to suggest that both occupations may share common risk factors despite their different work environments and lifestyles. The paper also noted that bus workers had the highest crude death rate.
Study limitations and confounders
Rather than establishing that London’s transport system itself causes high mortality rates, this study is the first to use longitudinal TfL data to show that bus and LU roles are associated with a higher risk of death than office-based TfL roles. However, the researchers stress that these findings should be interpreted in light of the study’s inherent limitations.
Most importantly, the TfL pension fund dataset lacked data that could account for confounding variables that are unrelated to work and can significantly impact health outcomes, such as smoking habits, alcohol intake, education, stress, and socio-economic differences. Additionally, older records and missing cause-of-death data for a wide range of occupations may have influenced the results.
Implications for worker health and future research
Despite these limitations, this study concludes that bus and LU workers in this cohort are at higher risk of several deaths, including deaths from lung cancer, than office workers, highlighting the need for further research and consideration of air quality management and health monitoring of transit operating staff.
