A 50-year analysis of Transport for London staff found higher mortality rates in bus and Tube roles than in office roles, raising important questions about workplace exposures, job conditions, and long-term worker health.
Study: Mortality in a cohort of transport for London workers. Image Credit: TiberPics / Shutterstock
In a recent retrospective study published in the journal Scientific Reports, researchers analyzed more than 50 years of data from 1960 to 2021, from the long-term follow-up of more than 117,000 Transport for London employees, to investigate disparities in mortality by job role.
Study findings revealed that bus and London Underground (LU) workers experienced significantly higher all-cause, respiratory, and cardiovascular mortality rates than office-based staff. Most notably, lung cancer risks were found to be more than double for LU workers and bus workers compared to office workers. These findings are consistent with possible occupational and environmental influences on long-term health in urban transport systems, but the study could not identify the specific causes of the observed differences.
Government-maintained records highlight London’s transport network as one of the busiest in the world, with estimates suggesting it facilitates ~26.1 million journeys per day. The city’s multimodal transportation system is operated by Transport for London (TfL), which reportedly employs an occupationally diverse workforce (n = ~30,000).
Occupational Stressors and Environmental Exposures
Previous studies have suggested that transport workers are routinely subjected to a range of physiological (e.g., prolonged sedentary postures) and mental (e.g., irregular shift work) stressors. Researchers further hypothesize that specific occupations may expose employees to high levels of environmental pollutants.
For example, in the underground tunnels, workers are expected to breathe air containing high concentrations of particulate matter (PM) generated by train wear, while bus drivers contend with street-level exhaust and traffic noise. While previous research has investigated the short-term health issues associated with TfL employment, the long-term trends in transport-associated occupational hazards remain unknown.
The present study aimed to address this knowledge gap by evaluating whether specific daily occupational hazards were associated with differences in mortality risk among TfL workers. The study employed a retrospective cohort design, with data obtained from the TfL Pension Fund. The dataset comprised 117,166 employees who joined the fund between 1960 and 2010, with follow-up data extending to October 2021.
Worker Categories and Analytical Approach
Study analyses categorized TfL workers (study participants) into four primary cohorts: 1. Bus Workers – A group that included bus drivers, ticket sellers, and bus conductors working on surface transport, 2. London Underground (LU) Workers – A broad category comprising everyone who worked in the LU organisation, including drivers and customer service staff, but also some office workers and engineers, 3. Engineers – A diverse group involved in maintenance and technical roles, and 4. Office Workers – Non-operational staff who performed desk-based roles and statistically served as the control (“reference”) cohort.
Participant data included pension fund records and death certificate information. Statistical analyses primarily used Cox proportional hazards models to compare mortality-based hazard ratios (HRs) across participants in the four primary cohorts. The models were notably adjusted for participants’ sociodemographic and occupational variables, particularly age, sex, employment duration, and the decade in which the worker joined the company.
All-Cause Mortality Differences Across Roles
Study findings revealed that participants in the bus and LU categories demonstrated significantly higher mortality risk than their office-bound counterparts (cohort 4). Descriptive statistics noted that over the 50 years, 37,849 deaths occurred within the full cohort.
All-cause mortality data showed that LU and bus workers demonstrated the highest mortality risk, with 23% and 17% higher mortality risk than control participants (HRLU 1.23, 95% CI 1.15–1.32; HRBus 1.17, 95% CI 1.09–1.25). Unexpectedly, engineers did not demonstrate a statistically significant difference from office workers in all-cause mortality results (HREng = 0.97).
Cause-Specific Mortality and Lung Cancer Risk
When evaluating the specific causes of death:
- Respiratory mortality - LU and bus workers demonstrated 73% and 44% higher respiratory mortality risk than office workers.
- Cardiovascular mortality - LU showed a 51% increase in risk, while bus workers showed a 30% increase.
Most notably, LU (HR = 2.85) and bus workers (HR = 2.48) were found to be more than twice as likely to die from lung cancer as office workers, although the study could not determine whether occupational air pollutants were directly responsible for this pattern.
Furthermore, while LU showed the highest hazard ratios in several analyses, LU versus bus worker mortality was found to be statistically similar, leading the researchers to suggest that both occupations might share common risk factors despite their different work environments or lifestyles. The paper also noted that crude mortality rates were highest in bus workers.
Study Limitations and Confounding Factors
The present study is the first to utilize long-term TfL data to show that bus and LU job categories were associated with higher mortality risks than office-based TfL roles, rather than establishing that London’s transport systems themselves cause higher mortality. However, the researchers emphasize that these findings should be interpreted alongside the study’s inherent limitations.
Most importantly, the TfL Pension Fund dataset lacked data that could account for confounding variables (e.g., smoking habits, alcohol use, education, stress, and socioeconomic differences), which could significantly influence health outcomes independently of the job. Furthermore, missing cause-of-death data for older records and broad job categories may have influenced the results.
Implications for Worker Health and Future Research
Despite these limitations, the study concludes that bus and LU workers in this cohort had higher risks of several mortality outcomes, including lung cancer mortality, than office workers, highlighting the need for further research and for consideration of air quality management and health monitoring for operational transit staff.
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