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Most tunnels are at least partly reinforced with concrete.
Transportation officials inspect the tunnels every two years. Each inspection takes about a day of peering at the inside walls and entrances to determine if any cracks or leaks exist and how serious they are. So far, any cracks that were recorded during inspections last year are slight and are not a danger to drivers, according to John Marks, a manager in the department's geotechnical unit. Oneonta Tunnel, built in 1914 near milepost 21.93 in the Columbia River Historic Highway area. Lined with timber, it's sealed and closed to the public.