Ten-mile hikes, wasp nests and forest fires marked an almost unfeasible feasibility study for a potential world-record road tunnel. Engineering geologists with Kleinfelder Inc., San Diego, are now working on a report, due by fall, for the Orange County Transportation Authority and Riverside County Transportation Commission. It will assess the possibility of building a pair of 50-ft-dia tunnels almost 12 miles long under the Cleveland National Forest in Southern California.
Engineers say tunnel-boring technology is not quite there yet, but might be by the time the agencies find funding and complete any final design for the estimated $8.5-billion project, which would alleviate traffic on overloaded State Route 91. The counties estimate S.R. 91 carries almost 300,000 vehicles a day now, with 425,000 vehicles a day by 2030. A major investment study narrowed several alternatives to the tunnel option.