Simplify the following text for a Grade 7 native English-speaking person.
Original: The freeway then runs along a viaduct through HÄ lawa Valley for about 6 m until it reaches the Tetsuo Harano Tunnels through the Ko ` olau Mountains .
Simplified: The highway then runs along a viaduct through Halawa Valley for about 6 miles . It then goes through the Tetsuo Harano Tunnels through the Koolau Mountains .