As sustainable investors, we focus on the biggest issues of our time, hunt for companies that can solve them and invest in the opportunities of maximum impact for maximum returns — and one key issue of the current era is transport.

Short-term problems in our auto industry are well documented, but we look beyond the profit warnings of 2018 and trade war tweets of 2019 to the underlying drivers. Emissions controls have been an issue for decades, but we believe something more fundamental is at work: The question is not whether we should buy diesel, petrol, hybrid or full electric, but rather whether to own a car at all.

Evidence for the underlying theme abounds but we are particularly interested in Marchetti's constant; the average time spent by a person for commuting each day. Analysis from a World Bank economist spanning from ancient Greece to modern-day Berlin concluded that humans will travel around 30 minutes to their place of work and 30 minutes back. Anything beyond that, over thousands of years of evidence, has proved unsustainable.

As we all know, 30 minutes to get anywhere in a modern city is ambitious and we need to recognize how fast urbanization is happening: globally, half the world's population already live in cities and the United Nations estimates more than two-thirds of us will do so by 2050.

Looking at a list of the world's most congested cities, Moscow, Istanbul, Bogota, Mexico City, Sao Paulo, London, Rio, Boston, Saint Petersburg and Rome, it is clear this is a global problem. Taking London as an example, the average speed of travel in a car for the final mile of a journey is just seven miles an hour versus a fast walking pace of 5 mph, according to the British Heart Foundation.

Where, then, is the opportunity? If driving is too energy and time-intensive and dangerous, what is the solution?

The congestion that so many of us face on a daily basis is not only unsustainable from a human tolerance perspective, it is also an economic waste. A 2013 study from the Centre for Economics and Business Research estimated the fuel costs, unnecessary expense and lost time from city congestion cost the United States, United Kingdom, France and Germany 0.8 percent of GDP a year.

Where, then, is the opportunity? If driving is too energy and time-intensive and dangerous, what is the solution? This is driving the notion of "peak car" and we feel analysts are missing what the public is increasingly realizing: Driving is no longer fun nor convenient. We have gone from half of Americans obtaining their driving licenses as soon as they were able in the 1990s to just over a quarter doing so in 2017. We are moving beyond car ownership to new mobility solutions.

We are investing in a wide range of solutions, from battery recycling that works to close the loop across electrified transport solutions to braking systems that will encourage high speed rail. Our holdings in Knorr-Bremse, Umicore and Trainline are other examples of how we believe we can make money for our clients via companies having positive impacts on our transport system.

Overall, we see the transport sector shifting focus from traditional internal combustion engine and powertrain cars to auto safety, multi-modal transport and trains. For our own welfare and the pollution and heat of the planet, we need to get out of the model of single ownership cars in clogged city streets and that continues to create opportunities for companies in the electric transport space.

Sustainable investment is often about freedom: to eat without consuming harmful chemicals, to build and manufacture without warming the planet, to shop for clothes without contributing to modern slavery or plastics in our oceans. In transport, while the freedom of the open road is vanishing fast, the freedom to move is just beginning.

Neil Brown is co-manager in Liontrust's sustainable investment team.