THINKING BIG : Case Study: Berlin : Engineers Design a New Heart for German City : Thousands of commuters and even a river are being rerouted around Europe’s biggest construction site. Critics worry about impact.

For more than two decades, motorists--and there are plenty in this land in love with the internal combustion engine--have pressed for the construction of a tunnel beneath the congestion in the heart of this sprawling city.

Now their dream is about to be fulfilled--and some Berliners are wondering if the lobbying hasn’t paid off too richly.

A huge park, the Tiergarten, lies in the middle of Berlin. An eight-lane, east-west thoroughfare carries traffic across its spreading lawns and into the neighborhoods beyond, but there is no major north-south street. A driver intent on such a journey must snake his or her way over narrow, zigzagging city streets and charming but jammed park lanes.

To a non-resident, a large tunnel, complete with lanes for both cars and trains, might sound like the obvious solution. But throughout the 1970s and 1980s, Berlin politicians dared not promote one. In those years the western side of this city was part of West Germany, land of the environmentalist Greens and the occasional eco-terrorist, and the proposition of doing anything to make the downtown more auto-friendly was a political non-starter.

But now Germany is united, and the seat of government is due to return here by the end of the century. Suddenly, Berliners have Europe’s biggest construction site right in their own city center.

A new chancellery must be built to house the head of united Germany’s federal government, as well as a new structure for the upper house of Parliament and various buildings for the 30,000 bureaucrats who will come here from Bonn, which was the seat of government of West Germany.

The historic Reichstag will be remodeled as the future home of the lower house of Parliament, and just a short distance to the south of these government projects a whole “new city” of luxury office buildings is going up.

So enormous are these works that they will involve the removal of enough earth and debris to fill a four-lane highway’s worth of dump trucks stretching from the Brandenburg Gate to Madrid. A project this size is both an engineer’s dream and nightmare, and it will place Berlin at the pinnacle of urban design, for good or ill, in the last decade of the millennium.

The need to convey Berlin’s thousands of daily commuters around this mess, and the future government quarter, has made the idea of overhauling the city’s traffic patterns not only a good bet politically but a practical necessity.

So, this fall, work will begin on a huge new central train station for Berlin, the centerpiece of the effort to reroute masses of cars, commuters and intercity travelers efficiently through the center of town.

The project will begin with the demolition of a small elevated-train station and the construction on its site of a vast, sunshine-filled rail complex--provisionally called the Lehrter Bahnhof--capable of handling the comings and goings of an expected 780 trains and 220,000 people each day.

Also planned for the site are new intercity rail routes, new subway tunnels to link the future government quarter to the city’s existing mass-transit system, and--most enticing of all, for Berlin’s drivers--the long-awaited auto tunnel, 2.4 miles of highway under the Tiergarten.

The cost of the rail project and auto tunnel alone--forget the surface infrastructure--is expected to come to $3.2 billion.

Advocates say a transportation system on the scale being contemplated is necessary for Berlin as it assumes its new role as physically the largest and, perhaps, culturally the most compelling capital in 21st Century Europe.

“Berlin is already much bigger than it was just a few years ago, because it was unified overnight,” said Ulrike Seidenfaden, a passenger-stations specialist with the German rail monopoly, Deutsche Bahn A.G. “And it will be even bigger in the future.”

But critics say the sheer breadth of the transportation project will throw Berlin’s already breakneck construction tempo out of whack and threaten the city’s jealously protected urban environment, dooming thousands of mature shade trees and undermining the foundations of historic buildings that survived four years of Allied bombing in World War II half a century ago.

Most alarming of all, they argue, the Lehrter Bahnhof and auto tunnel run counter to Berlin’s traditional pattern of urban development: a decentralized, neighborhood-based scheme that has, for generations, given much of this major city an unusually green and small-town feel.

Much consternation has arisen over the project’s construction techniques, some of which have never before been used in Berlin. Some of the tunnels, for instance, will be bored underground using machines normally devoted to cutting tunnels through Swiss mountains. Berliners, by contrast, are accustomed to seeing their subways built by workers who first dig a trench and then put a cover on it.

Plans also call for divers to pour some cement foundations underwater since Berlin’s water table is very high--if you excavate the hole almost immediately fills with water--and not all foundation excavation can be pumped out. At the same time, the River Spree, the main waterway meandering through Berlin and contributing mightily to the city’s park-like feel, will be temporarily rerouted to make way for the construction workers.

“None of these engineering feats alone is revolutionary,” Seidenfaden, the train station specialist, said. “But bringing them all together, under our timetable--that’s a logistical feat.”

The schedule calls, in fact, for the first tunnels to be built in a brisk two years to make way for the work on government buildings.

This alarms Michael Cramer, a Greens member of the Berlin Senat, or parliament, and his party’s senior official in Berlin for transportation policy.

Cramer noted that while construction of the train station and tunnels is in progress, 27 million cubic meters of water will have to be pumped out of the soil--as much as Berlin’s 3.5 million residents use in a typical month. And he said that although the water eventually will be replaced, the pumping could cause the water table under the Tiergarten to drop deep enough and for a long enough time to endanger thousands of trees.

In addition, Cramer said, some of Berlin’s most famous buildings may be damaged by the ground-water changes. The much-photographed Reichstag, the Berlin Dome and the Zeughaus, a museum, all rest upon oak pylons, just as buildings do in Venice, he pointed out.

“These pylons are stable as long as they are surrounded by water,” he said. “But if they come into contact with air, they would rot, and then the buildings would suffer.”

Construction officials respond that they plan to plant more than 10,000 new trees once all construction is completed--more than enough to replace any that are chopped down or deprived of water. In addition, they intend to use special water-extraction methods that will replace the ground water so quickly that no architectural harm can be done.

“The engineers are confident,” Cramer said, “but they need time to figure all these techniques out, and at the same time they are under tremendous deadline pressure.”

And even if the trees and buildings are spared, critics such as Cramer worry that the new network of rail lines--and especially the auto tunnel--will jeopardize the very spirit with which Berlin has grown up.

Berlin, Cramer noted, is a city composed of 23 proud and independent boroughs, and lacking in any central downtown. Each borough has its own center, and each has its own character and idiosyncrasies. Some are sleepy and dull, others are jumping with street life, some are elegant, and still others are marked by the drab, barracks-like facades that were beloved of East German city planners.

“Other cities are very envious of Berlin’s neighborhoods,” Cramer said. “The new central train station will push development toward the downtown. With a central train station, everything will just go in and out, downtown and back again. It will make Berlin a centralized city, with all the problems that centralized cities have.”

Reshaping Berlin

The center of this sprawling German city is being rebulit with a new auto tunnel, subway and rail routes, a vast train station called Lehrter Bahnhof and more government buildings. The work will prepare Berlin to return as Germany’s seat of government by the end of the century.