Well, after a bit of a hiatus we’re back. This one involves some weighty topics, and was a challenge to boil down. There was also some internal conflict over not being perfect. But here goes:

Before all the biologists in the room point out that active transport actually refers to the way living cells move molecules against a concentration gradient… let me give you our definition:

“Active Transport is getting from A to B by any means other than private vehicle or taxi. This includes, but is not limited to: walking, running, jogging, marching (with or without a band), cycling, roller-skating, roller-blading, skate-boarding, long-boarding, hover-boarding, scooting, segwaying… or using public transport.”

Win-Win Planet, 2021

Physical activity and health

Active transport involves physical activity. This is pretty obvious for walkers and cyclists, but even people who use public transport take on average 30% more steps per day than those who rely on cars.

We’ve known this is beneficial for health and longevity for some time. The earliest scientific study was a 1950 cohort of London bus drivers and conductors. Whilst the bus drivers spent their work days sitting, the conductors ran up and down the stairs selling tickets. This study showed the overall risk of developing heart disease was 40% lower for conductors than drivers. In conductors that did develop disease, this occurred later in life and was less likely to be fatal.

This discovery was followed a slew of studies demonstrating that physical activity reduced risks of incident heart disease, type 2 diabetes, and all-cause mortality, including after adjustment for obesity/ BMI. In other words; physical activity is probably more important for health and longevity than weight. The reason there has been so much focus on BMI in medical science is that it is easy to measure accurately. Physical activity is difficult to measure accurately, unless you put people in a laboratory, which then doesn’t represent a real world setting. As a result it’s hard to know exactly how much physical activity you need for a longer, healthier life; but it seems that every little helps.

Physical inactivity

The benefits of being a bus conductor were quickly realised, but it took us a little longer to work out what else that study hinted at. We had forgotten to consider the drivers.

There is now also strong evidence that physical inactivity (i.e. sitting for long periods) is a major risk factor for cardiovascular disease, diabetes, some cancers, metabolic syndrome etc… And when I say major, it’s comparable to smoking. This is because sitting in chairs causes our leg muscles to “switch off” and stop producing the enzyme that breaks down the trigylercides (blood fats) they normally burn up for energy. So triglyceride levels climb, eventually damaging blood vessels and causing fat accumulation in the liver and pancreas. The bottom line is that playing squash once a week may not compensate for sitting down for the rest of the time.

The good news is that even light activity (standing, taking short walks) to break up sitting time can greatly reduce your triglyceride levels and disease risk. Taking active transport builds exercise into your daily routine, helping you combat inactivity without thinking about it.

Brain health

It gets better too, because physical activity also improves your mental health and cognitive function. It boosts dopamine, serotonin and endorphins, resulting in improved mood and greater feelings of happiness. Even low-intensity exercise such as a brisk 20-minute walk each day is as effective as medication for treating mild to moderate depression, and can improve symptoms in other mental health conditions. This level of activity can also improve your memory, concentration, and productivity. Pedestrians and cyclists also tend to spend more time on quieter streets, and walk/cycle paths. These are often near green spaces and are just nicer places to be than busy roads.

On the other hand, driving for long periods in heavy traffic can make you feel tense, annoyed, or even trigger full-blown road rage! These feelings are common among drivers, and have negative impacts on your mental health and cognitive function. If you have to drive, choosing routes with more roadside vegetation can increase tolerance to frustration for yourself and other drivers, making your trip safer and more pleasant.

It probably goes without saying that cars are expensive to buy, register, maintain, fuel and park. So reducing your use of private vehicle transport may also save you money and ease financial stress… especially if you can eliminate a car from your household.

What about the planet?

Well, you can probably guess that transport is a fairly large contributor to greenhouse gas (GHG) emissions and climate change. Electricity & heat production is still the emission juggernaut globally, but transport takes second place. It accounts for 16% of total GHG emissions worldwide, although there is wide variation by country. Transport comprises 28% of emissions in the USA, making it the largest emitting sector… in the world’s second largest emitting nation. As electricity generation slowly (too slowly!) shifts to renewable sources, emissions from this sector have started to plateau. Transport emissions however, continue to climb steadily in most countries, and are now the fastest growing source of GHG emissions.

Methods of transport

Individually, we all need to get around. Collectively, we need rapid emission reductions across all sectors to limit global warming to 1.5-2°C, the less damaging end of our potential futures. So which forms of transport are best?

As you can see below (and knew anyway), petrol or diesel cars and flights emit the most GHG (measured in CO₂eq) per kilometre. Long-haul flights appear better per kilometre because takeoff and landing are the most energy intensive part of a flight. But of course, travelling such long distances releases more CO₂eq overall.

As you can also see, the best way to cut transport emissions is taking active transport!

Other low-emission wins for the planet include electric cars and carpooling. They may also be wins for you, espececially if you enjoy travelling with others and reducing long-term costs. Urban buses have a slightly higher footprint than other mass transit due to their lower occupancy, and being petrol vehicles that stop and start frequently. This could be reduced by transport companies converting to electric buses/ trams.

There have been attempts to quantify the carbon footprint of cycling based on what the cyclist eats, but this writer isn’t going to entertain that sort of unfair comparison here. Although some diets can indeed rival the emissions of driving a large car… everybody eats, not just cyclists. We consider walking or cycling essentially zero-carbon travel, and will open the dietary can-of-worms in another post.

Our city air

Of course, cars emit more than just CO₂. A cocktail of other gases (CO, SO₂, NO₂, ozone, volatile organic compounds) and particlulate matter are also released from road traffic. And unlike CO₂, these air pollutants can be directly harmful to humans.

The biggest culprit seems to be fine particles <2.5 micrometres in size (known as PM_2.5), which are small enough to enter the bloodstream via the lungs. There they can damage cells and induce respiratory diseases, heart disease and stroke. Ambient air pollution is a leading risk factor for disease globally, causing an estimated 4.2 million premature deaths from these diseases each year. You may have heard higher numbers quoted – this is because ambient and indoor air pollution are often grouped together in reports.

Traffic is a major contributor to ambient air pollution in cities worldwide, and the main cause in high income countries. The megacities in middle income countries (Delhi, Beijing, Karachi etc) have the highest levels of air pollution, bearing the combined effects of heavy traffic and industrial pollution. Geography also contributes when wind currents, pressure systems and hills conspire to trap smog over a city.

Air pollution can be reduced by using cleaner-burning (or electric) vehicles and industrial processes, and reducing traffic volume. Huge reductions have been achieved in many European cities through Clean Air Acts, congestion taxes, and investments in public transport infrastructure, with corresponding reductions in air pollution-related deaths. However, only a handful of countries in the world have PM_2.5 levels below the WHO recommended “safe” limits. These are the high income countries with low population density: Scandinavia, Canada, Australia and New Zealand.

Ultimately, to combat both climate change and air pollution, we need to create walk- and cycle-friendly cities, and transition to clean electric mass transit without delay.

OK I see the benefits… but I don’t know if I can do it

I get it. Maybe you live in an inaccessible area, start work at 5am, or would have to cycle with your toddler through a blizzard. Maybe you’d have to catch 3 buses and a tram to see your lover. Many cities and towns are not well set up for active transport, and this isn’t your fault.

Here are my suggestions on how to start:

• Say NO to short car trips. A recent survey in NZ found around one third of all car trips are less than 2km, which is about a 25 minute walk. Two thirds of trips are under 6km, which is about a 25 minute bike ride. So walk, or cycle those short trips. You’ll slash your emissions and reap the benefits!
• Make your next car electric. Electric vehicles (EVs) consume on average 58% less energy than petrol cars over their lifetimes, and this gap is widening. As energy generation shifts to renewables, batteries become more efficient and recycling increases, EVs are becoming even cleaner over time. Average EV emissions in the US have decreased by 10% over the last 5 years. They also produce very little air pollution.
• Car-pool (share your ride). It’s more social, and as the chart shows, a ride shared is a carbon footprint halved!
• Car-share (share your vehicle). Not everyone has to own their own car, and it’s cheaper to share. You could share a vehicle with other members of your household, or join a car-sharing service like Car Next Door.
• Go car-free. This will not be possible for everyone, but it’s my preferred option. No registration, no parking, no getting stuck in traffic, no expensive repairs, no fines, no emissions, no worries! 😉

Final thoughts

When it all seems too hard and you find yourself back in the driver’s seat, shaking your fist at someone who can’t seem to use turn-signals and despairing at the state of the world, it’s worth remembering a couple of things. Taking active transport on some occasions is better than not at all, so don’t be too hard on yourself if you can’t do it all the time. The phrase “carbon footprint” was actually created by the petroleum giant BP, to shift attention and responsibility from the industry to the consumer. But they know that consumers often don’t have a lot of alternatives.

Your choices do make a difference and your actions can influence others, but ultimately this is a big political and socioeconomic issue that can’t be solved single-handedly by you. So get active when you can, raise your concerns to your local council and government, and demand better public transport and safe walk- and cycle-ways in your city, region or country. Vote for representatives with good active transport policies, and hold them accountable. Because we need healthy, enjoyable and climate-friendly towns and cities, just as much as the planet.