From taxis to buses, trams and trains, there are a range of options for getting around our towns and cities.



The way these vehicles are fueled is changing, however, with hybrid taxis and hydrogen buses becoming increasingly common. Sometimes, the transition can be on a large scale: last year, for example, authorities in China announced that the Shenzhen Bus Group had replaced all 5,698 of its buses with electric vehicles.



California-based Emily Castor Warren is head of Autonomous and Urban Mobility at the World Economic Forum. She told CNBC's "Sustainable Energy" that there were a number of things that legislators and policymakers could focus on when it comes to efficiency.

"In a city transportation context, I think it really comes down to mileage efficiency, energy efficiency and cost efficiency," she said. "They want to know that the service they're providing to the public is going to have the least impact on the infrastructure, not cause congestion, not have negative impacts on the environment and allow them to provide the most service with the least amount of cost to the government."

While electric buses may offer an enticing alternative to ones fueled by gasoline, things aren't as simple as they seem. The source used to generate the electricity used by an electric bus is crucial.



"You actually have no guarantee that an electric bus is going to have a better energy footprint than a combustion engine bus," Castor Warren said. "I mean, just imagine if all that energy were coming from coal — it wouldn't be any better."



The development of buses that can operate without fossil fuels, Castor Warren explained, was a significant development. "Once you've done that, you can start to focus on all the ways that we can bring renewable power on to our grid," she said.



"The good news is that that's been happening really rapidly in recent years. You look at the cost of solar energy production, the cost of wind energy — they've been coming down. And so that means that, over time, we've been getting more and more and more renewable power on the grid."



When talking about the ways in which people will move around urban areas in the future, it's important to note just how big a role walking and cycling can play. Described by the European Commission as being "healthy, clean and cheap," cycling has become an incredibly popular mode of transport in cities such as Copenhagen and Amsterdam.



"We have a lot of bikes," Marie Kastrup, who is head of Copenhagen's Bicycle Program, told "Sustainable Energy" earlier this year. "Copenhageners own five times more bicycles than cars and we have around 375 kilometers of separated bicycle tracks," Kastrup said.

In other major cities around the world, cycle hire schemes — which allow people to rent a bicycle for a limited amount of time to complete a journey — are becoming a viable alternative to buses, subways and cabs. In London, for example, there were more than 600,000 cycle hires on the city's Santander Cycle Hire Scheme in January alone.



The WEF's Castor Warren pointed to trains and buses as being the most efficient vehicles for urban transport. "The larger the vehicle, the more people you can put inside it, the better that footprint is going to look," she said.



"You want to promote mass transit and invest as a city in those new, really efficient forms of high-capacity mass transport technologies, while also making sure that there's a variety of options so that people have a way to get to those trains and buses."