20.06.2025 - Article

This study examines the exposure of bus drivers in Switzerland to physicochemical risks (noise, vibration, electromagnetic fields, etc.).

Previous studies have found that the health of Swiss bus drivers has generally deteriorated over the past few decades. However, we have no data on exposure to physical and chemical hazards that would help us understand this change in the health of bus drivers. It is therefore necessary to collect such data.

The aim of this study is to carry out measurements on buses and subsequently apply the results regarding exposure to physico-chemical risks to the entire Swiss bus fleet.

Using the bus inventory created previously (https://www.trapheac.ch/fr/30092024-article), we selected 10 buses representative of the evolution of the bus fleet in Switzerland. We then carried out measurement campaigns on these buses to measure noise, floor and seat vibrations (known as whole-body vibrations), high-frequency and low-frequency electric fields, magnetic fields, fine dust (https://www.bafu.admin.ch/fr/poussieres-fines), ultrafine particles and the air exchange rate (the number of times the entire volume of air is replaced in a room/bus in one hour). We then modelled the exposure values for physico-chemical risks for almost all the buses in the inventory. This enabled us to create a bus-exposure matrix. Minibuses were excluded as their technology is too different. To understand changes in exposure to physico-chemical risks, we cross-referenced the data from the bus-exposure matrix with data collected in 2022 as part of the survey on the health of bus drivers (history of buses driven).

The bus exposure matrix contains 705 bus models and the corresponding exposure values for physico-chemical risks. All measured values are below the limit values. As a general rule, noise and high-frequency electric fields are higher in urban areas. In the long term, working conditions for bus drivers have generally improved. Average noise levels, vibrations and pollution inside buses have fallen significantly since the 1980s. However, certain factors have increased, such as noise peaks and electric fields, due to advances in on-board technology. One negative aspect concerns air circulation, which is now less effective than before, which can be detrimental during long journeys without frequent stops.

Modern buses are generally quieter, produce less vibration and offer better protection against pollution, which improves working conditions for drivers. However, certain new risks are emerging (electromagnetic fields, ventilation), highlighting the importance of continuing to improve vehicle design.

The strength of this study lies in its use of an advanced statistical method known as the Integrated Nested Laplace Approximation (INLA). INLA is a method that enables data to be analysed quickly and reliably in complex situations. Instead of running the computer for a very long time to test thousands of possibilities (the standard method), INLA uses mathematical shortcuts to provide accurate estimates directly. In practical terms, this provides a better understanding of the links between bus characteristics and exposure to various physico-chemical risks, whilst saving a great deal of computing time and maintaining accurate results. To do this, INLA solves the problem analytically, much like a sat-nav that predicts traffic based on a few key sensors rather than monitoring every car on the road. One limitation of the study is that all exposure modelling is based on just 10 buses. A larger number of buses would have yielded more accurate results. The other limitation is that no measurements were taken on minibuses. As their technology differs too greatly from that of other buses, we were unable to model exposure values for minibuses. The bus-exposure matrix therefore does not include minibuses.

This study has established the world’s first bus-exposure matrix. It paves the way for a new method of attributing exposure in studies based solely on the vehicles used.

This study provides a tool for estimating exposure levels to physico-chemical risks based solely on the bus model driven. This will enable research to be carried out into physico-chemical risks and the health of bus drivers.