What if you could make transportation carbon-neutral without getting rid of the internal combustion engine? That’s the idea behind Synhelion, a Swiss startup that’s developed a new synthetic gas powered by the sun. The so-called “solar fuel” is drop-in ready and can be used in place of traditional fossil fuels. As The World’s Transportation Correspondent Jeremy Siegel reports, experts say the product could play a major role in reducing the carbon footprint of air travel.