KAWASAKI -- More than three decades after the idea was first put forward, an expressway beneath Tokyo Bay opened Thursday with simultaneous ceremonies in Kanagawa and Chiba prefectures.

The new Tokyo Bay Aqualine incorporates the world's longest undersea tunnel for motor vehicles, linking Kawasaki to Kisarazu, Chiba Prefecture. Drivers can now cross Tokyo Bay in roughly 15 minutes.

The expressway consists of a 9.5-km undersea tunnel that starts in Kawasaki, a 4.4-km bridge from Kisarazu, two man-made islands -- one with a five-story parking building -- and additional access roads. About 150 vehicles driven by invited guests participated in parades that started separately from both the Kawasaki and Kisarazu sides Thursday morning.

The two columns of vehicles met on the man-made island where the "Umihotaru," or sea firefly, service area has been built in Tokyo Bay. The sea firefly is a plankton that glows at night and has become the symbol of the new 15.1-km expressway.

Chiba Gov. Takeshi Numata, Construction Minister Tsutomu Kawara and the Crown Prince and Princess attended the main ceremony on Umihotaru, one of the two artificial islands that connect the undersea tunnel and bridge section of the highway.

"(The road) will contribute to the development of not only the bay area but also the whole metropolitan district," said Kanagawa Gov. Hiroshi Okazaki, describing the construction as "the last major project of the century."

But whether the expressway will be economically successful remains to be seen, as many experts remain doubtful and local businesses complain of expensive toll tickets.

From the beginning, the project met with criticism and a lack of enthusiasm from local businesses. The daily traffic projection has already been lowered from 33,000 vehicles to 23,000 vehicles.

Japan Highway Public Corp. was also forced to reduce the ticket price from 5,050 yen one-way by car to 4,000 yen for the first five years after the opening. "If you take a taxi from JR Kawasaki Station to Kisarazu by the Aqualine, it will probably cost around 16,000 yen, including 2,000 yen that the driver will ask you to pay to help lessen the cost of the return trip to Kawasaki (by the Aqualine)," one Kawasaki taxi diver said. "It is so expensive for customers that the road doesn't mean much for us."