Modes of Transport

End date: 
Friday, 2 May, 2014
The Aim: 

To illustrate how the levels of pollution we are exposed to as we travel around London vary greatly between different routes and different modes of transport.


The Participants: 

The study was proposed and produced in collaboration with the London Borough of Camden and Client Earth as part of their Healthy Air Campaign. It involved six London residents: 

  • Ted normally walks to and from work and uses buses occasionally.
  • David lives in south London near a busy road. He normally uses a car and he is worried about the air he breathes from other traffic on the road.
  • Rose tries to reduce her exposure to air pollution when cycling or walking by avoiding busy roads. 
  • Carole cycles to and from work regularly and is concerned about air pollution.
  • Lalitha lives in central London, she likes to walk to and from work but suffers from asthma and finds that the air is too 'heavy', which has put her off walking. She now takes the bus instead.
  • Richard normally cycles around London and is becoming more concerned about the long term health implications of exposure to air pollution.


The Method: 

The participants met up in central London during an afternoon rush hour and were given portable pollution monitors and GPS watches. Four of the participants travelled from A to B along the same busy route using different modes of transport, recording pollution levels as they went. The instruments measured the concentration of black carbon particles to assess exposure to diesel vehicle exhaust. The following modes of transport were used by the participants to travel along the chosen route:

  • bus 
  • car
  • walking
  • cycling

The two remaining participants followed a quieter route away from the busy roads on foot and by bicycle.


The Results: 

A short film showing the results of the experiment can be watched here:

The main finding was that the participants travelling inside vehicles were exposed to the highest levels of air pollution, whereas those taking active travel (walking and cycling) were exposed to the lowest.

The car driver was exposed to the highest levels of air pollution by a wide margin; this is because he was sitting in his car right amongst the fumes from other vehicles on the road, particularly while queuing. These fumes enter the car through vents and windows and can take longer to disperse.

The person travelling by bus experienced the second highest levels air pollution, lower than the person in the car but higher than the cyclist using the same busy route. This demonstrates that it is often not the case that we can escape air pollution by sitting inside a vehicle.

The cyclist was not only the quickest to complete the journey, but he was also the person exposed to the lowest pollution levels.

Despite taking the longest to complete the journey the person walking was exposed to about half the pollution of the person travelling by car.

Perhaps not surprisingly, the cyclist and the walker that used the quiet route were exposed to lower levels of air pollution on average compared with the participants that used the busy route.


The Outcome: 

This experiment provided clear local evidence that shifting to active travel modes, such as cycling and walking, can have the additional benefit of reducing your exposure to air pollution, particularly if you chose quieter routes. 

The video created by Client Earth has had international exposure through You Tube and the Guardian website, helping to raise awareness and dispel preconceived views in other urban areas.

The experiment will be repeated at a later date to assess the impact of different breathing rates on each travel mode, i.e., comparing the dose of air pollution breathed, rather than the exposure concentration.


Contact Details: 

Project Coordinator: Andrea Lee (