Travel by bus to help improve our city's air quality

3 years ago Wed 27th Mar 2019

It may not sound like much, but just one of our double decker buses with its Euro 6 engine - carrying upwards of 70 people - gives off far less harmful emissions than a brand new diesel car. And if thousands of people committed to this change it could have a significant impact of the air quality here in Southampton.

Clean Air Facts

  • A Euro 6 diesel bus emits on average 10 times less NOx per passenger/km than a Euro 6 diesel car

  • Diesel cars are the biggest contributor to roadside NOx emissions in the UK, contributing 35% of emissions compared with just 16% for buses and coaches

  • A Euro 6 standard bus emits fewer emissions overall than the average diesel Euro 6 car despite having 15 to 20 times the capacity

  • Buses are an inherently clean way to travel - a fully loaded double decker bus can take up to 75 cars off the road, reducing congestion and pollution

  • The latest generation of clean diesel British buses deliver huge environmental and economic benefits and are key to tackling the UK’s air pollution crisis

  • Congestion will bring average traffic speeds in the UK’s busiest cities down from 17mph to 12mph by 2030, resulting in higher emissions

  • Since 2015, the sector has already invested around £700 million in England outside London on over 3,000 new Euro 6 or equivalent buses

Greenhouse gas emissions

A standard 5 door car with 4 passengers in it produces twice as much CO2e / passenger km compared to a fully laden bus.

SMMT average g CO2 /km for cars produced in 2017 : 121 g CO2/km (source). Assuming 4 passengers in the car, each passenger has 30.25 g CO2 /km. The average occupancy of a car in the UK is around 1.6 people per journey, if 2 people were travelling in a car, then their associated CO2/km would be 60.5 g CO2/km.

LowCVP average g CO2e/km for double deck diesel bus at Euro VI in 2017: 1303.9 g CO2 /km. Assuming a passenger capacity of 84, a full bus would result in each km producing 15.52 go CO2/km. A bus that is running at half capacity, has a CO2 impact of 35.2 g CO2/pass km.


  • All bus technologies are clean at Euro VI.

  • Euro VI bus technologies perform as good in terms of NOx than Euro VI diesel cars – NOx target for diesel cars at Euro 6 is 0.08 g NOx/km. Average DD diesel at Euro VI is 0.33 g NOx/km. Could look to include data from DfT testing demonstrating real world performance of diesel cars is much worse than target… (DfT Vehicle Emissions Test Programme for Cars)

  • Retrofit scheme CVRAS sets NOx target of 0.5 g NOx as Euro VI equivalent level – technologies proven under lab conditions. Again lower than Euro VI diesel car

Chart showing major decrease in emissions from Euro 5 to Euro 6 diesel engines