It’s true that diesel-powered trains emit a lot more polluting greenhouse gas than electric trains. That’s why most western countries with adequate electrical generation and distribution grid capacity are switching to electric propulsion. Other benefits are lower maintenance costs and faster acceleration. Energy, normally dissipated as heat during braking, can be returned to the grid to reduce overall energy consumption.
Electric propulsion is generally mandatory for passenger trains running more than 200kph as their high energy demands cannot be met with diesel engines and associated on-board fuel tanks. But, below 200kph diesel power remains a viable power option, particularly for operation with high-performance passenger trains with a maximum speed of around 175kph.
Although electricity is considered non-polluting it is only so when generated with emissions-free renewable power such as wind, solar, hydro-electric and nuclear. But the catch is that the manufacture and installation of power distribution infrastructure (transformers, overhead catenary and cables) is fairly emissions intensive. They can also be visually intrusive.
The very latest diesel passenger locomotives meet Environmental Protection Agency Tier 4 emissions (or its European equivalent) whereby exhaust aftertreatment (like your car’s catalytic converter) drastically reduces damaging oxides of nitrogen and carbon particulates. Carbon dioxide remains a problem but, typically, a diesel-powered passenger train emits about half the greenhouse gas per passenger/km than short-haul passenger aircraft on journeys up to about 800km.
Diesel-powered passenger trains can operate on freight lines owned by CN and CP as these freight carriers do not currently permit overhead electrical power equipment.
Ontario must eventually transition to electric trains in areas of high population density and eventually rural areas, where feasible. But High-Performance Rail using modern, low emission diesel engines is an economical and time-efficient interim solution that will make passenger railways appealing to more travelers while minimising taxpayer risk and cost.