Abstract: A long tunnel structure for covering a depressed highway or railway, which provides substantially increased ventilation and over which parkland or building structures can be built. In the latter case the columns of the tunnel structure can be used as columns for supporting the building. The tunnel structure is comprised of support structures for roof beams, and a plurality of parallel roof beams supported by the support structures extending laterally over the depressed highway. Each of the roof beams is comprised of an elongated slab and a pair of spaced elongated upwardly projecting slab legs each spaced from longer edges of the slab and extending along the slab. The slabs are spaced apart a distance sufficient to allow air flow therebetween. Elongated closure slabs are disposed over the ends of the legs of adjacent slabs along the beams to form vents between adjacent legs of adjacent beams.