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Location: Boston, Massachusetts, USA
Completion Date: 2004
Traffic Flow: 343.000 vehicles per day
Deepest Point: 36,5m below Red Line subway
Dirt excavation: 11.5 million m³
Cost: over $11 billion
Beneath Boston, one of the oldest cities of the United States,
over 5000 people are working on the most expensive
and technologically advanced civil engineering project in America.
The estimated cost of this project is over eleven billion dollars,
surpassing thereby even the construction of the Panama Canal.
All this money is spend to the realization of a five kilometers long expressway.
This motorway would be eight- to ten-lanes wide, replacing herewith the existing,
elevated, and extremely congested, six-lane highway.
Officially this project is known as the central artery/tunnel project,
but the locals just like to call it the Big Dig.
Not that strange if you imagine that more than 11.5 million cubic meters
of dirt will be excavated in the eighteen years it will take to complete the whole project.
The original highway dates back to the 1940s,
and was built for the same reason as this project nowadays; traffic jams.
This two kilometers long, elevated, highway, suggested by the Public Works Department,
runs right through the center of Boston. They intended to let it cooperate with another highway,
called the Inner Belt. Through traffic could use the Inner Belt highway,
thereby bypassing the heart of Boston. Local traffic could use the raised highway.
The latter one got many access and exit points, so the people could get to every neighborhood from that central artery.
Ten years later the actual construction of the highway began.
But it became clear very soon that this innovative idea wouldn't turn out to be as effective
and impressive as everyone had anticipated. The new central artery was a hideous,
twelve meters high, green barrier between the north end of Boston and the central district.
Another disappointment was caused by the 27 (!) on- and off-ramps.
Because of the numerous ramps, the through traffic had to contend with the traffic weaving on
and off the road. Also the merge and breakdown lanes were lacking,
what didn't help very much to improve the situation.
Bearing in mind all those problems, the Public Works Department decided to sink the remainder of the highway in a tunnel.
The construction of the Inner Belt highway would help to improve the just mentioned problems,
however inhabitants along the building-path of the highway protested against this project.
This resulted in the canceling of the Inner Belt highway construction,
however not in the disappearance of the mentioned problems obviously.
Eventually the whole project (without the Inner Belt) had been completed in 1959,
and displaced hereby more than 20.000 citizens and demolished over a thousand buildings.
Because of all this the central artery today carries the local traffic and the through traffic,
yet it had only been designed to process the local traffic.
The highway easily carries about 75.000 vehicles a day,
but the 190.000 of these days causes a traffic jam of six to eight hours per day.
When nothing is done to solve this than the traffic jam will be immense in 2010,
since the traffic flow is expected to have been doubled in 2010.
Not only is this bottle-neck a waste of time, also the safety is in danger;
the accident rate is four times as high as the national average on interstate highways.
Adding up all of this, one has estimated that the annual cost are about half a billion dollars.
It's clear that something had to be done to solve this dilemma.
Adding an extra corridor to the existing highway wasn't a solution,
because construction-workers would occupy one lane during the construction.
This would have a disastrous effect on the already congested highway.
The only option was to build a brand new highway right beneath the existing one.
This way the citizens can live on, without having to deal with the extra traffic jams and the noise.
Drawback of this solution is the high cost to keep the cars 'driving' during construction-time,
since a number of temporary ways and ramps have to be built to realize this ambition.
While the problems were known a long time ago,
the thinking about the solution started just in 1982.
For the actual construction one had to wait even longer.
Nine years later, in 1991, the project began with the building of the Ted Williams tunnel
and a bypass road through the south of Boston. The Ted Williams tunnel,
which unburdens the busy airport routes, was the first part of the whole project to be delivered up.
This tunnel carries about 98.000 vehicles every day.
Another 245.000 cars will drive through Boston via the new central artery;
when it is finished of course. At that time the old highway will be demolished and replaced by parks and open space.
To build this new central artery and to let the citizens live on without too much inconvenience,
the invention of slurry walls was put into practice.
A slurry wall is nothing more than a concrete wall running from the surface down to bedrock.
These walls are placed on either side of the area that is excavated.
And in the end these slurry walls will form the actual walls of the new central artery.
This is just one example of the many challenges the civil engineers come across,
many other challenges lie ahead. For instance the ten lane Charles-river bridge.
This will be the widest cable-stayed bridge in the world.
And after that the engineers will again encounter other unforeseen problems.
This will go on until every problem has been solved and the project has been finished.
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