Construction is underway to convert the last southern arc section of Madrid’s M-30 beltway into a tunnel. Part of an ongoing highway refurbishment program called Calle 30, the 2,000-ft-long, 69- to 85-ft-wide cut-and-cover tunnel will replace the above-ground highway section, which will be routed below the footprint of a now-demolished soccer stadium. Landscaping atop the new underground structure will extend the Madrid Río urban park, further enhancing mobility between adjacent neighborhoods. Spanish contractor Ferrovial, which is carrying out the 20-month project in a joint venture with infrastructure developer Acciona, will maintain traffic flows in both directions along the M-30 using a temporary detour beneath the demolished stadium. n