This typically shows that a bus emits more than twice the carbon dioxide per passenger km than a car with four passengers. For example, the latest 2022 Defra statistics show that an average petrol car emits 170g of carbon dioxide vs 96g for an average bus, and 35g for national rail per passenger km.

That’s an excellent question, but the answer isn’t a single number. The CO₂ emissions of a bus per kilometer depend heavily on several key factors.

Here’s a breakdown, from general averages to specific details:

General Averages (Good for a Ballpark Figure)

• Average Diesel Bus: 0.82 - 1.19 kg of CO₂ per passenger-kilometer.
  • This is the most common metric, which factors in how many people are on board. An empty bus emits a lot per passenger, while a full one emits very little per person.
• Average Diesel Bus (vehicle-only): 800 - 1,200 grams of CO₂ per vehicle-kilometer.
  • This is the total tailpipe emission for the bus itself, regardless of passengers.

Key Takeaway: A typical 40-foot diesel bus emits roughly 1 kg of CO₂ per km it travels. But this number changes dramatically based on the factors below.

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Major Factors That Change the Emission Rate

1. Fuel Type (The Biggest Factor):
   • Diesel (Conventional): The baseline. ~1,100 g CO₂/km (vehicle).
   • Compressed Natural Gas (CNG): Emits about 15-20% less CO₂ than diesel.
   • Hybrid Diesel-Electric: Can reduce CO₂ by 20-35% depending on driving conditions.
   • Battery Electric Bus (BEB): Zero tailpipe emissions. The “well-to-wheel” emissions depend entirely on how the local electricity is generated (e.g., coal vs. wind/solar). In