Roads haven’t changed much in the last few thousand years. The Romans had the basic idea—a large aggregate covered in smaller stones, topped with something smoother—that we still use today. But the rock used in base and subbase of today’s roads, as well as the concrete and asphalt used on the surface, has to be mined and hauled to wherever it’s needed. Both are costly and not environmentally friendly. But now researchers are looking into cheaper, more sustainable, and smarter ways to build streets and highways. In this episode we will take a closer look at what the new asphalt can do for the environment and for the construction industry.   Guest: Christopher Elofsson, project manager at Vällsta asphalt plant.    Guest: Abubeker Achmed, senior researcher working for the Swedish National Road and Transport Institute.    Guest: Jiqing Zhu, senior researcher working for the Swedish National Road and Transport Research Institute.