A milelong tunnel in Zion National Park was considered an engineering marvel when it was built in 1930, but it has caused some headaches for park officials this year.

Superintendent Harold Grafe said Tuesday the 59-year-old tunnel was built to handle vehicles 136 inches tall and 94 inches wide. But the modern tour bus is 102 inches wide.To counter the problem, the park will begin a one-year escort service guiding nearly 6,000 recreation vehicles and tour buses through the tunnel.

This year, the service will cost the park an estimated $50,000. An oversize vehicle takes seven minutes to travel through the tunnel.