SBB trains are powered by electric motors and thus do not, generally, emit any airborne pollutants. The air is only polluted by the exhaust gases from building heating systems and diesel locomotives, or the fine dust generated by abrasion of wheels, brakes and rails.

Thanks to electrification, the passenger and freight trains operated by SBB cause practically no airborne pollution. The only exception is the fine dust that has increasingly come to the attention of the medical profession in recent years as it can penetrate deep into the respiratory tract.

Fine iron dust.

Scientific studies have shown that SBB generates around 1000 tons of fine dust each year. This amounts to some three percent of the entire quantity of fine dust in Switzerland. The fine dust ejected and blown around by the trains consists mostly of iron particles abraded from brakes, wheels and rails.

Although the fine dust arising from rail operations is significant in respect of the volumes generated, it is less hazardous to health - because of its composition and size - than the carcinogenic soot particles generated by the combustion of diesel, for instance. Measurements have shown that rail traffic, even along busy routes, is responsible for only 1.5 to 2 micrograms of fine dust per cubic metre. The limit value is 20 micrograms. Shutting down sections of track in times of high fine-dust pollution would therefore not alleviate the situation at all. On the contrary: road traffic would increase further, causing the concentration of airborne particles to shoot up.

Particle filters.

To reduce soot emissions by the diesel locomotives it uses for shunting work and track maintenance, SBB's procurements of diesel locomotives since 2004 have focused entirely on vehicles equipped with particulate filters. Nowadays, around 80 percent of installed engine power, or 75 percent of vehicles, are fitted with these filters (2011). Vehicles without filters that are due to remain in service for some time are being gradually retrofitted. In this respect, SBB leads the way among European railway companies.