Umihotaru (海ほたる) is a highway rest stop in the middle of the sea between Tokyo Bay and Chiba prefecture and what makes it unique is that you need to travel through a tunnel underneath the sea and it rises again to the surface at Umihotaru and you can stop to take in the view.
The world’s most unusual parking lot
Umihotaru was built in 1997 on an artificial island designed to structurally support the transitional point of the underground tunnel from Kanagawa and the bridge from Chiba. The tunnel section has been highly praised for its advanced engineering .
The Tokyo Bay Aqua Line, or Trans-Tokyo Bay Expressway as it was originally known, was first surveyed in 1966. Its purpose was to reduce the travel time between the two industrial regions, Kawasaki(Kanagawa) in the east and Kisarazu(Chiba) in the west.
It’s basically a toll highway consisting of two 10km-long underwater tunnels through the Kawasaki waters, one 5km-long bridge over Chiba waters, and two man-made islands in between. Umihotaru offers a huge parking area and a ventilation tower called The Tower of Wind (Kaze no to).
One of the world’s largest marine construction projects
After approximately 20 years of surveys and 10 years of construction, the Tokyo Wan Aqua-Line Expressway opened to traffic on Dec. 18, 1997.
From design to execution, its construction represented a convergence of state-of-the-art technologies and know-how of the time. Many new technologies and construction methods were developed and implemented, and its construction was also referred to as the “Apollo project of civil engineering.” Engineers had to overcome a vast variety of challenges, ranging from the soft soil of the sea floor to natural conditions such as wind, tide, and earthquakes, as well as marine traffic and environmental conservation in Tokyo Bay.
The boring wheel used to dig the undersea tunnel
The boring wheel used to dig the undersea tunnel is one of those must see things at Umi Hotaru. It took 31 years to study the possibility to build a road connection in the middle of the Tokyo Bay and build the Aqualine, which opened to traffic in December 1997 after 8 years of construction. The total cost reached… 1.44 trillion yens (11 billion dollars)! The best NON PERFORMING ASSET in Japan. I was impressed by this 14m cutter face, which was used to make a tunnel under the sea.
The rest stop has a unique parking structure that houses five floors of restaurants, shops, and observation decks
Umihotaru generates electricity from the near-constant winds blowing across the Tokyo Bay
How to Get There
Umihotaru can be reached from either side of Tokyo Bay (Kawasaki or Kisarazu).There are buses that go to the island departing from Kawasaki and Kisarazu stations. Make sure that you check the schedule before planning your trip.
If you are driving from Tokyo, Yokohama , or Kawasaki , connect to the Aqua-Line by the Bayshore Route or National Route 409 at both the Kawasaki Ukishima junction and Ukishima interchange. From the Chiba or Kisarazu area, the Aqua-Line connects to the Aqua Renraku Expressway and National Route 409 at the Kisarazu Kaneda interchange.