Tokyo Bay Crossing

Japan is stepping up construction of modern highways. The country has a modest system of expressways. Virtually all are toll roads, built and operated by a self-financing national government corporation Nihon Doro Kodan (NDK). Japan’s expressway length is about 4,000 miles. France with aound 8,000 toll road miles is the world leader. NDK gets about $16 billion in toll revenues annually.

Some 3,500 miles of new tolled expressways are either under construction, in design or the subject of route studies in Japan and expected to be built by 2010. Major longitudinal routes, east-west on trhe major island Honshu are about three-quarters developed leaving quite a number of east-west sections. Also about a dozen transverse or north-south links are being made. Some of the most difficult and spectacular new work is inside or on the fringes of major built up areas. The Tokyo area with over 10 million people has a series of mainly radial expressways poorly interconnected. But ambitious plans are under to build new highways throughout the Tokyo area, including

• several new radials

• a Tokyo Bay Ring Road, following the oval shoreline shape of the bay

• completion of a Outer Ring road or beltway at a radius of about 8 miles

• construction of a nearly circular Metropolitan Inter-city Expressway at about 25 mile radius

When completed in perhaps 15 years time this will give Tokyo a network of expressways not unlike that of Chicago or the San Francisco Bay area in the U.S. Being entirely tolled at quite high toll rates, traffic flows are likely to be less and as a result lane requirements will be smaller.

One of the most innovative projects is the Trans-Tokyo Bay Highway currently under construction by a special purpose corporation. The highway crosses the pinched middle section of Tokyo Bay with a 6 mile long tunnel section, artificial islands and 2.7 miles of bridge — 9.4 miles in total. The Fort McHenry tunnel under Baltimore harbor used to claim to be the world’s longest underwater vehicular tunnel at 7200 feet between portals. Sydney Harbor’s later tunnel is 7680ft, Øresund’s tunnel 12,300ft (see “Denmark’s Big Bridges” report) and the Tokyo Bay one 31,170ft (just shy of 6 miles.) This crossing is two-thirds tunnel, one third bridge, the reverse of the Øresund arrangement. The cost discrepancy is huge too. Where the Øresund crossing is coming at around $4.5 billion, the Trans-Tokyo Bay crossing is a staggering $14 billion. And the Øresund provides 2 rail lines plus 4 highway lanes whereas the Tokyo Bay crossing only provides the 4 highway lanes.

Most modern tunnels under bays are built by dredging a channel and lowering huge prefabricated concrete tube sections into the trench, joining them and sealing them, then pumping them dry. Tokyo’s is unusual in that it is a mined tunnel 40’ below the seabed using circular mining shields. Being six miles long it needs an intermediate vent tower, that is a 325’ diameter circular structure that sticks up in the middle of the bay, supposedly protected from errant ships by enormous triangular plan diverters. A half mile long artificial island is being built for the tunnel-bridge transition. The major shipping channels are over the tunnelled section where there is 70’ of water, so the 2.7 ml bridge is a straightforward box girder job with clearance for large sailing boats. The whole thing is built initially for 4 lanes of traffic but the tunnel venting and portals are designed to take a third two lane tube later and the bridge is designed to take extra lane deck sections applied to each edge. Construction began in 1989 and completion is due 1997.

The driving distance from central Tokyo half way around the bay is about 70 miles and the new crossing will reduce the distance to about 20 miles. 33,000 vehicles a day are predicted to start with and 64,000 after 20 years. No word yet on what the toll will be. (Contact: Trans-Toyko Bay Highway Corp fax 03 3239 4858.)