Rail emissions can be a concern as railway switching yards are often located near populated areas and rail lines may pass through areas where people live. Trains in Canada are powered by very large diesel engines. Thus the pollutants emitted by trains are similar to those emitted by large trucks. However, railway locomotives produce a relatively higher proportion of sulphur dioxide (SO2) emissions than on-road diesel engines since the diesel fuel used by locomotives has a higher sulphur content.
Since 2006, federal regulations (Sulphur in Diesel Fuel Regulations) have required that on-road diesel engines
use ultra-low-sulphur diesel fuel with less than 15 mg/kg sulphur content. These same regulations allow locomotives to use diesel fuel with up to 500 mg/kg sulphur content until May 31st, 2012, at which
point locomotives will also be required to use ultra-low-sulphur diesel fuel.
Locomotive emissions in Canada are regulated by Transport Canada and Environment Canada. These agencies are working to align Canadian locomotive standards with those in the United States (Transport Canada).
According to Canada's National Pollutant Release Inventory (Environment Canada) rail transportation accounts for approximately
1.6% of total emissions of fine particulate matter emissions in British Columbia, as well as 1.2% of SO2 emissions and 9.5% of NOx emissions in British Columbia.