What is the CO2 emissions of a diesel bus?
On typical service, a standard urban diesel bus emits about 0.9 to 1.2 kilograms of CO2 for every kilometer it travels, depending on design, load, and driving conditions. Emissions per passenger kilometer can be much lower when the bus carries many riders.
How diesel bus emissions are measured
Emissions are usually reported in two ways: per vehicle-kilometer (the CO2 released by the bus for each kilometer it travels) and per passenger-kilometer (CO2 divided by the number of passengers carried). The exact figures depend on fuel efficiency, engine technology, weight, route characteristics, and idling times.
Engine technology and fuel efficiency
Engine design, fuel economy, and after-treatment systems (such as SCR for NOx, diesel particulate filters) influence how much fuel is burned and, therefore, how much CO2 is produced per kilometer. Improvements over generations typically reduce fuel use and CO2 intensity, even as other emissions like NOx and particulates are addressed.
Typical emissions by bus type
- Urban 12–14 meter diesel bus: approximately 0.9–1.2 kilograms CO2 per kilometer
- Articulated (long) diesel buses: approximately 1.1–1.5 kilograms CO2 per kilometer
- Coach/intercity diesel buses: approximately 0.6–0.9 kilograms CO2 per kilometer
Note: These ranges reflect common operating conditions in many cities and can vary with fuel efficiency, maintenance, route grade, average speed, and how often climate control is used.
Emissions per passenger-kilometer
Riders influence the footprint per kilometer; the more people aboard, the lower the CO2 per passenger-km tends to be. The following figures assume typical urban occupancy ranges and standard diesel bus performance.
- Very light occupancy (~20 passengers): roughly 40–60 grams CO2 per passenger-kilometer
- Moderate occupancy (~30–40 passengers): roughly 25–33 grams CO2 per passenger-kilometer
- High occupancy (~60–80 passengers): roughly 12–17 grams CO2 per passenger-kilometer
These estimates illustrate how crowding can dramatically change the per-rider impact, making high-occupancy buses comparatively efficient on a per-rider basis.
Context and takeaway
Direct CO2 emissions from diesel buses are tied to fuel consumption, so improvements in engine efficiency, weight reduction, and route optimization lower their carbon footprint. Switching to alternative propulsion—such as hybrid, biofuel blends, or electric buses—can further reduce or eliminate tailpipe CO2 emissions, particularly on routes with high ridership or long life cycles.
Summary
Diesel buses generally emit about 0.9–1.2 kg CO2 per kilometer for urban operation, with higher figures for heavier or less efficient designs and lower figures for more aerodynamic coach configurations. Per passenger-kilometer, emissions depend heavily on how many people ride; higher occupancy dramatically lowers the footprint per rider. Across the board, fuel efficiency and occupancy are the two biggest levers for reducing a diesel bus’s CO2 impact, while alternatives such as hybrids, biofuels, and electric propulsion offer other paths to lower emissions.
