Transport – October 2016

In honour of International Walk to School Month, our theme for October 2016 is TRANSPORT. Getting around is important ... but there are environmental considerations at every turn. 
So, which forms of transport have the least environmental impact, and is there any way to achieve sustainable transport? Read on to find out ... 


Why does it matter?

There are several environmental considerations when thinking about transport: 

• Carbon dioxide emissions (see chart, below) 
• Air quality 
• Safety 
• Congestion/mental health 

In the modern world, we have so many choices of how to get around. For work or pleasure, we can enjoy the luxury and convenience of our own vehicles, be they cars or motorbikes or bicycles – or we can take shared public transport. For shorter journeys, including the journey to school, many of us can walk. Walking has the least environmental impact of any form of transport, scoring very low on all the four considerations above. But for many journeys, it's not practical. Cycling also scores very low – only safety a possible concern – and is a great way to go further. But if it's raining, or you have lots to carry, cycling or walking are not popular choices. 

Public transport has the next least environmental impact: although overall energy consumption and pollution are higher per vehicle, it is shared by many passengers. Congestion is not such an issue, because one vehicle can carry many passengers, and does not need a parking space. And overall, public transport is safer than personal vehicles. Airliners are a form of public transport – but they tend to go much further, and many of the journeys their passengers are making are non-essential. Motorbikes contribute less to congestion, and most produce less carbon dioxide than cars – although there is nearly always only one passenger.

Cars are the most convenient – with comfort and protection from wind and rain, the luxury of warmth on a cold day, freedom to go wherever, whenever. But regular, petrol-engined cars produce the most carbon dioxide per person per mile (see chart below); they also produce nitrogen oxides that threaten health and contribute to acid rain; in cities, they create traffic jams and they require parking spaces. With global warming a real threat to our future, many new designs of car are being considered and developed to reduce the environmental impacts of the motor car. See the box below to find out about some of them. 

It is worth noting that we also increasingly have choices of where and whether to get around. Choosing not to go on a holiday to the other side of the world, for example, will save two long-haul flights from your carbon footprint. 

Zero carbon dioxide per mile (apart from what you breathe out, which comes from your food, and is therefore renewable).


70 grams carbon dioxide per passenger kilometre – the figure varies hugely, of course, so this is an average.


120 to 250 grams per passenger per kilometre carbon dioxide – varies with traffic, number of passengers etc.


175 carbon dioxide per passenger kilometre (average). Aeroplane journeys are generally much longer than other journeys.


Reducing your transport footprint

Transport is one of the major contributors to global warming – not least because motorised vehicles (cars, motorbikes, lorries, buses, trains, aeroplanes) obtain the energy they need to move from fossil fuels – either directly in their engines or indirectly if they are electric vehicles. Electric vehicles tend to have lower greenhouse gas emissions, because they do not run when the vehicles are stationary.  

The 'per person' greenhouse gas emissions of a car are halved when two people are in the car, and reduced more if there are more passengers. That's why some cities have 2+ lanes that encourage multi-occupancy of cars. Public transport is by definition a multi-passenger solution to getting around – and bus lanes are a way to encourage people to take public transport, reducing their overall carbon footprint. 

For shorter journeys the best way to reduce carbon footprint associated with travel is to walk or cycle. 

Alternative cars

Cars are very convenient, and their popularity unlikely to wain. But increasing awareness of the contributions of cars to climate change have led manufacturers and consumers to seek ways to reduce the environmental impact. Many new cars have smaller, more efficient engines, with start-stop technology that stops the engine automatically when the car is stationary. Some even have 'regenerative brakes' that recapture energy normally wasted during braking, turning it into electricity to charge the battery. This is particularly important in hybrid cars and electric cars whose wheels are powered by electric motors. See the links section below for a video that explains both these technologies. 

Of course, ditching old cars to encourage the production of new, more energy-efficient new cars requires huge amounts of energy, and therefore results in tonnes of greenhouse gas emissions. Many car makers are developing hydrogen-powered vehicles, which either burn hydrogen directly or combine it with oxygen in a fuel cell produce electricity. In either case, the only waste product is water. Energy is needed to produce the hydrogen gas – and today, most of that energy comes from burning fossil fuels. But in a future in which most energy is generated by renewable sources such as wind and hydroelectric power, hydrogen vehicles, and electric vehicles, could have zero carbon emissions. 

Useful links ...

Here are some links for you to investigate further: 

• International Walk to School Month is co-ordinated in the UK by Living Streets: website or Facebook.  
• More detailed information about carbon dioxide per passenger per mile:
• Union of Concerned Scientists on cars and global warming
Short video explaining start-stop and regenerative braking (which is called brake energy recuperation in the video).