Sand Island was originally known as Quarantine Island during the 19th century as quarantine ships would drop off passengers who they felt had a contagious disease. Back in those days there was no bridge to the main island of Oahu. It was just far enough away to be a prison of sorts. During World War II, the island was used as an Army internment camp where prisoners of war were kept. In the 1970's, a group over 100+ homeless native Hawaiians cleaned up Sand Island and made it their home. However, in the 1980's the island was reclaimed by the State of Hawaii and turned into an industrial and recreational area.
When the Sand Island Access Road Bridge was first built in 1962 by Colonel John Rudolph Slattery of the Army Corps of Engineers, it was originally a 2-lane draw bridge. However, in the 1980's it was sealed permanently and has 4 lanes plus the concrete walkway/bike path you are about to geocache on. You can still see the control tower which is unmanned now. Today the bridge is the lifeline for supplies coming into Hawaii by ship and over 2,000 trucks a day carry cargo over it.
When you go to Sand Island Recreational Park you will see half buried bunkers and abandoned military towers from WWII