Tokyo Bay Aqua-Line, Bridge-tunnel highway in Kawasaki, Japan.
Tokyo Bay Aqua-Line is a highway crossing Tokyo Bay between Kawasaki and Kisarazu through an underwater tunnel and bridge combination. The route runs for 15.1 kilometers and carries four traffic lanes that could be widened to six in the future.
Construction started in 1986 and required engineers to develop new tunneling methods for the soft seabed and deep water. The tunnel reaches 60 meters below sea level, excavated with shield machines measuring 14 meters in diameter.
The Umihotaru rest area, positioned at the junction between tunnel and bridge sections, functions as a maritime observation point for Tokyo Bay marine activities.
The highway cuts travel time between Kawasaki and Kisarazu from 90 minutes to 30 minutes. The Umihotaru rest area sits at the midpoint and offers views across the bay.
At Umihotaru there is a small museum with exhibits showing the construction techniques and the creation story of the roadway. Visitors can view models of the tunneling machines and photographs from the building phases.
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